--- a/src/main/java/nl/cwi/monetdb/client/JdbcClient.java
+++ b/src/main/java/nl/cwi/monetdb/client/JdbcClient.java
@@ -10,6 +10,7 @@ package nl.cwi.monetdb.client;
 
 import nl.cwi.monetdb.util.CmdLineOpts;
 import nl.cwi.monetdb.util.Exporter;
+import nl.cwi.monetdb.util.MDBvalidator;
 import nl.cwi.monetdb.util.OptionsException;
 import nl.cwi.monetdb.util.SQLExporter;
 import nl.cwi.monetdb.util.XMLExporter;
@@ -23,7 +24,6 @@ import java.io.PrintWriter;
 import java.net.HttpURLConnection;
 import java.net.URL;
 import java.sql.Connection;
-import java.sql.DriverManager;	// required as it will load the nl.cwi.monetdb.jdbc.MonetDriver class
 import java.sql.DatabaseMetaData;
 import java.sql.ResultSet;
 import java.sql.ResultSetMetaData;
@@ -308,7 +308,7 @@ public final class JdbcClient {
 		con = null;
 		final String database = copts.getOption("database").getArgument();
 		try {
-			con = DriverManager.getConnection(
+			con = java.sql.DriverManager.getConnection(
 					"jdbc:monetdb://" + host + "/" + database + attr,
 					user,
 					pass
@@ -689,8 +689,8 @@ public final class JdbcClient {
 						out.println("\\l<uri>  executes the contents of the given file or URL");
 						out.println("\\i<uri>  batch executes the inserts from the given file or URL");
 						out.println("\\vsci    validate sql system catalog integrity");
-					//	out.println("\\vsni    validate sql system netcdf tables integrity");	// depends on netcdf library
-					//	out.println("\\vsgi    validate sql system geom tables integrity");	// depends on geom library
+					//	out.println("\\vsni    validate sql system netcdf tables integrity");	// depends on availability of netcdf library on server
+					//	out.println("\\vsgi    validate sql system geom tables integrity");	// depends on availability of geom library on server
 						out.println("\\vsi <schema>  validate integrity of data in the given schema");
 						out.println("\\vdbi    validate integrity of data in all user schemas in the database");
 						out.println("\\? or \\h this help screen");
@@ -1321,1306 +1321,3 @@ final class Table {
 	}
 }
 
-/**
- * MonetDB Data Integrity Validator program (MDBvalidator) can
- * a) validate system tables data integrity in system schemas: sys and tmp
- *    this includes violations of:
- *		primary key uniqueness
- *		primary key column(s) not null
- *		unique constraint uniqueness
- *		foreign key referential integrity
- *		column not null
- *		column maximum length for char/varchar/clob/blob/json/url columns which have max length > 0
- * b) validate user schema tables & columns data integrity based on available meta data from system tables & system views
- *		primary key uniqueness
- *	TODO primary key column(s) not null
- *		unique constraint uniqueness
- *	TODO foreign key referential integrity
- *		column not null
- *		column maximum length for char/varchar/clob/blob/json/url columns which have max length > 0
- *
- * More possible validations for future
- *		col char/varchar/clob/blob/json/url minimum length (some columns may not be empty, so length >= 1)
- *		col with sequence (serial/bigserial/autoincrement) in range (0/1/min_value .. max_value)
- *		col value is valid in domain (date/time/timestamp/json/inet/url/uuid/...)
- *		col in list checks (some columns may have only certain values which are not stored in a table or view (eg as fk))
-		SELECT * FROM sys.table_partitions WHERE "type" NOT IN (5,6,9,10);	-- 5=By Column Range (1+4), 6=By Expression Range (2+4), 9=By Column Value (1+8), 10=By Expression Value (2+8), see sql_catalog.h #define PARTITION_*.   Note table_partitions is introduced in Apr2019  "33"
- *		col conditional checks (column is not null when other column is (not) null)
-		-- i.e.: either column_id or expression in sys.table_partitions must be populated
-		SELECT "column_id", "expression", 'Missing either column_id or expression' AS violation, * FROM "sys"."table_partitions" WHERE "column_id" IS NULL AND "expression" IS NULL;
-		SELECT "column_id", "expression", 'column_id and expression may not both be populated. One of them must be NULL' AS violation, * FROM "sys"."table_partitions" WHERE "column_id" IS NOT NULL AND "expression" IS NOT NULL;
- *
- * designed and created by Martin van Dinther 2020
- *
- * @author Martin van Dinther
- * @version 0.1
- */
-
-final class MDBvalidator {
-	private static final String prg = "MDBvalidator";
-	private Connection con;
-	private int majorversion;
-	private int minorversion;
-
-	private boolean verbose = false;	// set it to true for tracing all generated SQL queries, see validateQuery(qry, ...)
-
-	MDBvalidator(Connection conn) {
-		con = conn;
-	}
-
-/*
-	public static void main(String[] args) throws Exception {
-		System.out.println(prg + " started with " + args.length + " arguments." + (args.length == 0 ? " Using default JDBC URL !" : ""));
-		// parse input args: connection (JDBC_URL), check systbls (default) or user schema or user db
-
-		String JDBC_URL = (args.length > 0) ? args[0]
-						: "jdbc:monetdb://localhost:50000/demo?user=monetdb&password=monetdb&so_timeout=14000";
-		if (!JDBC_URL.startsWith("jdbc:monetdb://")) {
-			System.out.println("ERROR: Invalid JDBC URL. It does not start with jdbc:monetdb:");
-			return;
-		}
-
-		Connection con = null;
-		try {
-			// make connection to target server
-			con = java.sql.DriverManager.getConnection(JDBC_URL);
-			System.out.println(prg + " connected to MonetDB server");
-			printExceptions(con.getWarnings());
-
-			long start_time = System.currentTimeMillis();
-
-			validateSqlCatalogIntegrity(con);
-			validateSqlNetcdfTablesIntegrity(con);
-			validateSqlGeomTablesIntegrity(con);
-
-			validateSchemaIntegrity(con, "sys");
-			validateDBIntegrity(con);
-
-			long elapsed = System.currentTimeMillis() - start_time;
-			long secs = elapsed /1000;
-			System.out.println("Validation completed in " + secs + "s and " + (elapsed - (secs *1000)) + "ms");
-		} catch (SQLException e) {
-			printExceptions(e);
-		}
-
-		// free resources
-		if (con != null) {
-			try { con.close(); } catch (SQLException e) { /* ignore * /  }
-		}
-	}
-*/
-
-	static void validateSqlCatalogIntegrity(final Connection conn) {
-		MDBvalidator mdbv = new MDBvalidator(conn);
-		if (mdbv.checkMonetDBVersion()) {
-			mdbv.validateSchema("sys", null, sys_pkeys, sys_akeys, sys_fkeys, sys_notnull, true);
-			mdbv.validateSchema("tmp", null, tmp_pkeys, tmp_akeys, tmp_fkeys, tmp_notnull, true);
-		}
-	}
-
-	static void validateSqlNetcdfTablesIntegrity(final Connection conn) {
-		MDBvalidator mdbv = new MDBvalidator(conn);
-		if (mdbv.checkMonetDBVersion()) {
-			// determine if the 5 netcdf tables exist in the sys schema
-			if (mdbv.checkTableExists("sys", "netcdf_files")
-			 && mdbv.checkTableExists("sys", "netcdf_dims")
-			 && mdbv.checkTableExists("sys", "netcdf_vars")
-			 && mdbv.checkTableExists("sys", "netcdf_vardim")
-			 && mdbv.checkTableExists("sys", "netcdf_attrs"))
-				mdbv.validateSchema("sys", "netcdf", netcdf_pkeys, netcdf_akeys, netcdf_fkeys, netcdf_notnull, false);
-		}
-	}
-
-	static void validateSqlGeomTablesIntegrity(final Connection conn) {
-		MDBvalidator mdbv = new MDBvalidator(conn);
-		if (mdbv.checkMonetDBVersion()) {
-			if (mdbv.checkTableExists("sys", "spatial_ref_sys"))	// No need to also test if view sys.geometry_columns exists
-				mdbv.validateSchema("sys", "geom", geom_pkeys, geom_akeys, geom_fkeys, geom_notnull, false);
-		}
-	}
-
-	static void validateSchemaIntegrity(final Connection conn, final String schema) {
-		MDBvalidator mdbv = new MDBvalidator(conn);
-		if (mdbv.checkSchemaExists(schema))
-			mdbv.validateSchema(schema, null, null, null, null, null, true);
-		else
-			System.out.println("Schema: " + schema + " does not exist in this database.");
-	}
-
-	static void validateDBIntegrity(final Connection conn) {
-		MDBvalidator mdbv = new MDBvalidator(conn);
-		Statement stmt = mdbv.createStatement("validateDBIntegrity()");
-		if (stmt == null)
-			return;
-
-		boolean hasUserSchemas = false;
-		ResultSet rs = null;
-		try {
-			// retrieve all non-system schemas
-			rs = stmt.executeQuery("SELECT name FROM sys.schemas WHERE NOT system ORDER BY name;");
-			if (rs != null) {
-				// for each user schema do:
-				while (rs.next()) {
-					String schema = rs.getString(1);
-					if (schema != null && !schema.isEmpty()) {
-						hasUserSchemas = true;
-						mdbv.validateSchema(schema, null, null, null, null, null, true);
-					}
-				}
-			}
-		} catch (SQLException e) {
-			printExceptions(e);
-		}
-		freeStmtRs(stmt, rs);
-		if (!hasUserSchemas)
-			System.out.println("No user schemas found in this database.");
-	}
-
-
-	private void validateSchema(
-		final String schema,
-		final String group,
-		final String[][] pkeys,
-		final String[][] ukeys,
-		final String[][] fkeys,
-		final String[][] colnotnull,
-		final boolean checkMaxStr)
-	{
-		boolean is_system_schema = ("sys".equals(schema) || "tmp".equals(schema));
-
-		if (pkeys != null) {
-			validateUniqueness(schema, group, pkeys, "Primary Key uniqueness");
-			validateNotNull(schema, group, pkeys, "Primary Key Not Null");
-		} else {
-			validateUniqueness(schema, true, "Primary Key uniqueness");
-		}
-
-		if (ukeys != null) {
-			validateUniqueness(schema, group, ukeys, "Unique Constraint");
-		} else {
-			validateUniqueness(schema, false, "Unique Constraint");
-		}
-
-		if (fkeys != null) {
-			validateFKs(schema, group, fkeys, "Foreign Key referential integrity");
-		} else {
-			validateFKs(schema, "Foreign Key referential integrity");
-		}
-
-		if (colnotnull != null) {
-			validateNotNull(schema, group, colnotnull, "Not Null");
-		} else {
-			validateNotNull(schema, is_system_schema, "Not Null");
-		}
-
-		if (checkMaxStr)
-			validateMaxCharStrLength(schema, is_system_schema, "Max Character Length");
-	}
-
-	/* validate uniqueness of primary key or uniqueness constraints based on static data array */
-	private void validateUniqueness(
-		final String schema,
-		final String group,
-		final String[][] data,
-		final String checkType)
-	{
-		final int len = data.length;
-		System.out.println("Checking " + minimumWidth(len,6) + (group != null ? " " + group : "") + " tables/keys  in schema " + schema + " for " + checkType + " violations.");
-
-		StringBuilder sb = new StringBuilder(256);	// reusable buffer to compose SQL validation queries
-		sb.append("SELECT COUNT(*) AS duplicates, ");
-		final int qry_len = sb.length();
-		String tbl;
-		String keycols;
-		for (int i = 0; i < len; i++) {
-			if (isValidVersion(data[i][2])) {
-				tbl = data[i][0];
-				keycols = data[i][1];
-				// reuse the StringBuilder by cleaning it partial
-				sb.setLength(qry_len);
-				sb.append(keycols).append(" FROM ");
-				if (!tbl.startsWith("(")) {	// when tbl starts with a ( it is a unioned table set which we cannot prefix with a schema name qualifier
-					sb.append(schema).append('.');
-				}
-				sb.append(tbl)
-				.append(" GROUP BY ").append(keycols)
-				.append(" HAVING COUNT(*) > 1;");
-				validateQuery(sb.toString(), schema, tbl, keycols, checkType);
-			}
-		}
-	}
-
-	/* validate uniqueness of primary key or uniqueness constraints based on dynamic retrieved system data from sys.keys */
-	private void validateUniqueness(
-		final String schema,
-		final boolean pkey,
-		final String checkType)
-	{
-		Statement stmt = createStatement("validateUniqueness()");
-		if (stmt == null)
-			return;
-
-		// fetch the primary or unique key info from the MonetDB system tables
-		StringBuilder sb = new StringBuilder(400);
-		sb.append(" FROM sys.keys k JOIN sys.tables t ON k.table_id = t.id JOIN sys.schemas s ON t.schema_id = s.id"
-				+ " WHERE k.type = ").append(pkey ? 0 : 1)	// 0 = primary keys, 1 = unique keys
-			.append(" and s.name = '").append(schema).append("'");
-		String qry = sb.toString();
-		final int count = runCountQuery(qry);
-		System.out.println("Checking " + minimumWidth(count,6) + " keys         in schema " + schema + " for " + checkType + " violations.");
-
-		ResultSet rs = null;
-		try {
-			sb.setLength(0);	// empty previous usage of sb
-			// fetch the primary or unique key info including columns from the MonetDB system tables
-			sb.append("SELECT s.name as sch_nm, t.name as tbl_nm, k.name as key_nm, o.name as col_nm, o.nr")
-			.append(" FROM sys.keys k JOIN sys.objects o ON k.id = o.id JOIN sys.tables t ON k.table_id = t.id JOIN sys.schemas s ON t.schema_id = s.id"
-				+ " WHERE k.type = ").append(pkey ? 0 : 1)	// 0 = primary keys, 1 = unique keys
-			.append(" and s.name = '").append(schema).append("'")
-			.append(" ORDER BY t.name, k.name, o.nr;");
-			qry = sb.toString();
-			rs = stmt.executeQuery(qry);
-			if (rs != null) {
-				String sch = null, tbl, key, col;
-				String prv_tbl = null, prv_key = null, keycols = null;
-				sb.setLength(0);	// empty previous usage of sb
-				sb.append("SELECT COUNT(*) AS duplicates, ");
-				final int qry_len = sb.length();
-				while (rs.next()) {
-					// retrieve meta data
-					sch = rs.getString(1);
-					tbl = rs.getString(2);
-					key = rs.getString(3);
-					col = rs.getString(4);
-					if (prv_tbl == null)
-						prv_tbl = tbl;
-					if (prv_key == null)
-						prv_key = key;
-					if (tbl.equals(prv_tbl) && key.equals(prv_key)) {
-						if (keycols == null)
-							keycols = "\"" + col + "\"";
-						else
-							keycols = keycols + ", \"" + col + "\"";
-					} else {
-						// compose validation query for the previous retrieved key columns
-						// reuse the StringBuilder by cleaning it partial
-						sb.setLength(qry_len);
-						sb.append(keycols)
-						.append(" FROM \"").append(sch).append("\".\"").append(prv_tbl).append("\"")
-						.append(" GROUP BY ").append(keycols)
-						.append(" HAVING COUNT(*) > 1;");
-						validateQuery(sb.toString(), sch, prv_tbl, keycols, checkType);
-						prv_tbl = tbl;
-						prv_key = key;
-						keycols = "\"" + col + "\"";
-					}
-				}
-				if (sch != null && prv_tbl != null && keycols != null) {
-					// compose validation query for the last retrieved key
-					// reuse the StringBuilder by cleaning it partial
-					sb.setLength(qry_len);
-					sb.append(keycols)
-					.append(" FROM \"").append(sch).append("\".\"").append(prv_tbl).append("\"")
-					.append(" GROUP BY ").append(keycols)
-					.append(" HAVING COUNT(*) > 1;");
-					validateQuery(sb.toString(), sch, prv_tbl, keycols, checkType);
-				}
-			}
-		} catch (SQLException e) {
-			System.err.println("Failed to execute query: " + qry);
-			printExceptions(e);
-		}
-		freeStmtRs(stmt, rs);
-	}
-
-	/* validate foreign key constraints based on static data array */
-	private void validateFKs(
-		final String schema,
-		final String group,
-		final String[][] data,
-		final String checkType)
-	{
-		final int len = data.length;
-		System.out.println("Checking " + minimumWidth(len,6) + (group != null ? " " + group : "") + " foreign keys in schema " + schema + " for " + checkType + " violations.");
-
-		StringBuilder sb = new StringBuilder(400);	// reusable buffer to compose SQL validation queries
-		sb.append("SELECT ");
-		final int qry_len = sb.length();
-		String tbl;
-		String cols;
-		String ref_tbl;
-		String ref_cols;
-		for (int i = 0; i < len; i++) {
-			if (isValidVersion(data[i][4])) {
-				tbl = data[i][0];
-				cols = data[i][1];
-				ref_cols = data[i][2];
-				ref_tbl = data[i][3];
-				// reuse the StringBuilder by cleaning it partial
-				sb.setLength(qry_len);
-				sb.append(cols).append(", * FROM ").append(schema).append('.').append(tbl);
-				if (!tbl.contains(" WHERE "))
-					sb.append(" WHERE ");
-				sb.append('(').append(cols).append(") NOT IN (SELECT ").append(ref_cols).append(" FROM ");
-				if (!ref_tbl.contains("."))
-					sb.append(schema).append('.');
-				sb.append(ref_tbl).append(");");
-				validateQuery(sb.toString(), schema, tbl, cols, checkType);
-			}
-		}
-	}
-
-	/* validate foreign key constraints based on dynamic retrieved system data from sys.keys */
-	private void validateFKs(
-		final String schema,
-		final String checkType)
-	{
-		Statement stmt = createStatement("validateFKs()");
-		if (stmt == null)
-			return;
-
-		// fetch the foreign key info from the MonetDB system tables
-		StringBuilder sb = new StringBuilder(400);
-		sb.append(" FROM sys.keys k JOIN sys.tables t ON k.table_id = t.id JOIN sys.schemas s ON t.schema_id = s.id"
-				+ " WHERE k.type = 2")	// 2 = foreign keys
-			.append(" and s.name = '").append(schema).append("'");
-		String qry = sb.toString();
-		final int count = runCountQuery(qry);
-		System.out.println("Checking " + minimumWidth(count,6) + " foreign keys in schema " + schema + " for " + checkType + " violations.");
-
-		ResultSet rs = null;
-		// TODO: finish FK validation implementation
-
-		freeStmtRs(stmt, rs);
-	}
-
-	/* validate NOT NULL constraints based on static data array */
-	private void validateNotNull(
-		final String schema,
-		final String group,
-		final String[][] data,
-		final String checkType)
-	{
-		final int len = data.length;
-		System.out.println("Checking " + minimumWidth(len,6) + (group != null ? " " + group : "") + " columns      in schema " + schema + " for " + checkType + " violations.");
-
-		StringBuilder sb = new StringBuilder(256);	// reusable buffer to compose SQL validation queries
-		sb.append("SELECT ");
-		final int qry_len = sb.length();
-		String tbl;
-		String col;
-		boolean multicolumn = false;
-		StringBuilder isNullCond = new StringBuilder(80);
-		for (int i = 0; i < len; i++) {
-			if (isValidVersion(data[i][2])) {
-				tbl = data[i][0];
-				col = data[i][1];
-				multicolumn = col.contains(", ");	// some pkeys consist of multiple columns
-				isNullCond.setLength(0);	// empty previous content
-				if (multicolumn) {
-					String[] cols = col.split(", ");
-					for (int c = 0; c < cols.length; c++) {
-						if (c > 0) {
-							isNullCond.append(" OR ");
-						}
-						isNullCond.append(cols[c]).append(" IS NULL");
-					}
-				} else {
-					isNullCond.append(col).append(" IS NULL");
-				}
-				// reuse the StringBuilder by cleaning it partial
-				sb.setLength(qry_len);
-				sb.append(col)
-				.append(", * FROM ").append(schema).append('.').append(tbl)
-				.append(" WHERE ").append(isNullCond).append(';');
-				validateQuery(sb.toString(), schema, tbl, col, checkType);
-			}
-		}
-	}
-
-	/* validate NOT NULL constraints based on dynamic retrieved system data from sys.columns */
-	private void validateNotNull(
-		final String schema,
-		final boolean system,
-		final String checkType)
-	{
-		Statement stmt = createStatement("validateNotNull()");
-		if (stmt == null)
-			return;
-
-		// fetch the NOT NULL info from the MonetDB system tables as those are leading for user tables (but not system tables)
-		StringBuilder sb = new StringBuilder(400);
-		sb.append(" from sys.columns c join sys.tables t on c.table_id = t.id join sys.schemas s on t.schema_id = s.id"
-				+ " where t.type in (0, 10, 1, 11) and c.\"null\" = false"	// t.type 0 = TABLE, 10 = SYSTEM TABLE, 1 = VIEW, 11 = SYSTEM VIEW
-				+ " and t.system = ").append(system)
-			.append(" and s.name = '").append(schema).append("'");
-		String qry = sb.toString();
-		final int count = runCountQuery(qry);
-		System.out.println("Checking " + minimumWidth(count,6) + " columns      in schema " + schema + " for " + checkType + " violations.");
-
-		ResultSet rs = null;
-		try {
-			sb.setLength(0);	// empty previous usage of sb
-			sb.append("SELECT s.name as sch_nm, t.name as tbl_nm, c.name as col_nm")	// , t.type, t.system, c.type, c.type_digits
-			.append(qry).append(" ORDER BY s.name, t.name, c.name;");
-			qry = sb.toString();
-			rs = stmt.executeQuery(qry);
-			if (rs != null) {
-				String sch, tbl, col;
-				while (rs.next()) {
-					// retrieve meta data
-					sch = rs.getString(1);
-					tbl = rs.getString(2);
-					col = rs.getString(3);
-					// compose validation query for this specific column
-					sb.setLength(0);	// empty previous usage of sb
-					sb.append("SELECT '").append(sch).append('.').append(tbl).append('.').append(col).append("' as full_col_nm, *")
-					.append(" FROM \"").append(sch).append("\".\"").append(tbl).append("\"")
-					.append(" WHERE \"").append(col).append("\" IS NULL;");
-					validateQuery(sb.toString(), sch, tbl, col, checkType);
-				}
-			}
-		} catch (SQLException e) {
-			System.err.println("Failed to execute query: " + qry);
-			printExceptions(e);
-		}
-		freeStmtRs(stmt, rs);
-	}
-
-	/* validate Maximum (Var)Char(LOB) Length constraints based on dynamic retrieved system data from sys.columns */
-	private void validateMaxCharStrLength(
-		final String schema,
-		final boolean system,
-		final String checkType)
-	{
-		Statement stmt = createStatement("validateMaxCharStrLength()");
-		if (stmt == null)
-			return;
-
-		// fetch the max char str len info from the MonetDB system tables as those are leading
-		StringBuilder sb = new StringBuilder(400);
-		sb.append(" from sys.columns c join sys.tables t on c.table_id = t.id join sys.schemas s on t.schema_id = s.id"
-				+ " where t.type in (0, 10, 1, 11)"	// t.type 0 = TABLE, 10 = SYSTEM TABLE, 1 = VIEW, 11 = SYSTEM VIEW
-				+ " and c.type_digits >= 1"		// only when a positive max length is specified
-				+ " and t.system = ").append(system)
-			.append(" and c.type in ('varchar','char','clob','json','url','blob')")	// only for variable character/bytes data type columns
-			.append(" and s.name = '").append(schema).append("'");
-		String qry = sb.toString();
-		final int count = runCountQuery(qry);
-		System.out.println("Checking " + minimumWidth(count,6) + " columns      in schema " + schema + " for " + checkType + " violations.");
-
-		ResultSet rs = null;
-		try {
-			sb.setLength(0);	// empty previous usage of sb
-			sb.append("SELECT s.name as sch_nm, t.name as tbl_nm, c.name as col_nm, c.type_digits")	// , t.type, t.system, c.type
-			.append(qry).append(" ORDER BY s.name, t.name, c.name, c.type_digits;");
-			qry = sb.toString();
-			rs = stmt.executeQuery(qry);
-			if (rs != null) {
-				long max_len = 0;
-				String sch, tbl, col;
-				while (rs.next()) {
-					// retrieve meta data
-					sch = rs.getString(1);
-					tbl = rs.getString(2);
-					col = rs.getString(3);
-					max_len = rs.getLong(4);
-					// compose validation query for this specific column
-					sb.setLength(0);	// empty previous usage of sb
-					sb.append("SELECT '").append(sch).append('.').append(tbl).append('.').append(col).append("' as full_col_nm, ")
-					.append(max_len).append(" as max_allowed_length, ")
-					.append("length(\"").append(col).append("\") as data_length, ")
-					.append("\"").append(col).append("\" as data_value")
-					.append(" FROM \"").append(sch).append("\".\"").append(tbl).append("\"")
-					.append(" WHERE \"").append(col).append("\" IS NOT NULL AND length(\"").append(col).append("\") > ").append(max_len);
-					validateQuery(sb.toString(), sch, tbl, col, checkType);
-				}
-			}
-		} catch (SQLException e) {
-			System.err.println("Failed to execute query: " + qry);
-			printExceptions(e);
-		}
-		freeStmtRs(stmt, rs);
-	}
-
-
-	/* Run a validation query.
-	 * It should result in no rows returned.
-	 * When rows are returned those are the ones that contain violations.
-	 * Retrieve them and convert the results (currently first 16 only) into a (large) violation string
-	 * Log/Print the violation.
-	 */
-	private void validateQuery(
-		final String qry,
-		final String sch,
-		final String tbl,
-		final String cols,
-		final String checkType)
-	{
-		Statement stmt = createStatement("validateQuery()");
-		if (stmt == null)
-			return;
-
-		ResultSet rs = null;
-		try {
-			if (verbose) {
-				System.out.println(qry);
-			}
-			rs = stmt.executeQuery(qry);
-			if (rs != null) {
-				final ResultSetMetaData rsmd = rs.getMetaData();
-				final int nr_cols = rsmd.getColumnCount();
-				final StringBuilder sb = new StringBuilder(1024);
-				final int maxprintrows = 16;
-				int row = 0;
-				String val;
-				int tp;
-				while (rs.next()) {
-					// query returns found violations
-					row++;
-					if (row == 1) {
-						// print result header once
-						for (int i = 1; i <= nr_cols; i++) {
-							sb.append((i > 1) ? ", " : "\t");
-							sb.append(rsmd.getColumnLabel(i));
-						}
-						sb.append('\n');
-					}
-					if (row <= maxprintrows) { // print only the first n rows
-						// retrieve row data
-						for (int i = 1; i <= nr_cols; i++) {
-							sb.append((i > 1) ? ", " : "\t");
-							val = rs.getString(i);
-							if (val == null || rs.wasNull()) {
-								sb.append("null");
-							} else {
-								tp = rsmd.getColumnType(i);	// this method is very fast, so no need to cache it outside the loop
-								if (tp == Types.VARCHAR || tp == Types.CHAR || tp == Types.CLOB || tp == Types.BLOB) {
-									sb.append('"').append(val).append('"');
-								} else {
-									sb.append(val);
-								}
-							}
-						}
-						sb.append('\n');
-					}
-				}
-				if (row > 0) {
-					if (row > maxprintrows) {
-						sb.append("...\n");
-						sb.append("Listed only first ").append(maxprintrows).append(" violations of ").append(row).append(" found!\n");
-					}
-					logViolations(checkType, sch, tbl, cols, qry, sb.toString());
-				}
-			}
-		} catch (SQLException e) {
-			System.err.println("Failed to execute query: " + qry);
-			printExceptions(e);
-		}
-		freeStmtRs(stmt, rs);
-	}
-
-	private int runCountQuery(final String from_qry) {
-		Statement stmt = createStatement("runCountQuery()");
-		if (stmt == null)
-			return 0;
-
-		ResultSet rs = null;
-		int count = 0;
-		try {
-			rs = stmt.executeQuery("SELECT COUNT(*) " + from_qry);
-			if (rs != null) {
-				if (rs.next()) {
-					// retrieve count data
-					count = rs.getInt(1);
-				}
-			}
-		} catch (SQLException e) {
-			System.err.println("Failed to execute SELECT COUNT(*) " + from_qry);
-			printExceptions(e);
-		}
-		freeStmtRs(stmt, rs);
-		return count;
-	}
-
-	private Statement createStatement(final String method) {
-		try {
-			return con.createStatement();
-		} catch (SQLException e) {
-			System.err.print("Failed to create Statement in " + method);
-			printExceptions(e);
-		}
-		return null;
-	}
-
-	private boolean checkMonetDBVersion() {
-		if (majorversion == 0 && minorversion == 0) {
-			// we haven't fetched them before.
-			try {
-				// retrieve server version numbers (major and minor). These are needed to filter out version specific validations
-				DatabaseMetaData dbmd = con.getMetaData();
-				if (dbmd != null) {
-					// System.out.println("MonetDB server version " + dbmd.getDatabaseProductVersion());
-					majorversion = dbmd.getDatabaseMajorVersion();
-					minorversion = dbmd.getDatabaseMinorVersion();
-				}
-			} catch (SQLException e) {
-				printExceptions(e);
-			}
-		}
-		// validate majorversion (should be 11) and minorversion (should be >= 19) (from Jul2015 (11.19.15))
-		if (majorversion < 11 || (majorversion == 11 && minorversion < 19)) {
-			System.out.println("Warning: this MonetDB server is too old for " + prg + ". Please upgrade MonetDB server.");
-			return false;
-		}
-		return true;
-	}
-
-	private boolean isValidVersion(final String version) {
-		if (version == null)
-			return true;	// when no version string is supplied it is valid by default
-
-		try {
-			int v = Integer.parseInt(version);
-			return minorversion >= v;
-		} catch (NumberFormatException e) {
-			System.out.println("Failed to parse version string '" + version + "' as an integer number.");
-		}
-		return false;
-	}
-
-	private boolean checkSchemaExists(final String schema) {
-		Statement stmt = createStatement("checkSchemaExists()");
-		if (stmt == null)
-			return false;
-
-		String sql = "SELECT name FROM sys.schemas WHERE name = '" + schema + "';";
-		ResultSet rs = null;
-		boolean ret = false;
-		try {
-			rs = stmt.executeQuery(sql);
-			if (rs != null) {
-				if (rs.next()) {
-					if (schema != null && schema.equals(rs.getString(1)))
-						ret = true;
-				}
-			}
-		} catch (SQLException e) {
-			System.err.println("Failed to execute " + sql);
-			printExceptions(e);
-		}
-		freeStmtRs(stmt, rs);
-		return ret;
-	}
-
-	private boolean checkTableExists(final String schema, final String table) {
-		Statement stmt = createStatement("checkTableExists()");
-		if (stmt == null)
-			return false;
-
-		String sql = "SELECT s.name, t.name FROM sys.tables t JOIN sys.schemas s ON t.schema_id = s.id WHERE t.name = '" + table + "' AND s.name = '" + schema + "';";
-		ResultSet rs = null;
-		boolean ret = false;
-		try {
-			rs = stmt.executeQuery(sql);
-			if (rs != null) {
-				if (rs.next()) {
-					if (schema != null && schema.equals(rs.getString(1))
-					 && table  != null && table.equals(rs.getString(2)) )
-						ret = true;
-				}
-			}
-		} catch (SQLException e) {
-			System.err.println("Failed to execute " + sql);
-			printExceptions(e);
-		}
-		freeStmtRs(stmt, rs);
-		return ret;
-	}
-
-	private void logViolations(
-		final String checkType,
-		final String schema,
-		final String table,
-		final String columns,
-		final String query,
-		final String violations)
-	{
-		StringBuilder sb = new StringBuilder(2048);
-		sb.append(checkType).append(" violation(s) found in \"")
-		  .append(schema).append("\".\"").append(table).append("\".\"").append(columns).append("\":\n")
-		  .append(violations)
-		  .append("Found using query: ").append(query).append("\n");
-		System.out.println(sb.toString());
-	}
-
-	private static void printExceptions(SQLException se) {
-		while (se != null) {
-			System.err.println(se.getSQLState() + " " + se.getMessage());
-			se = se.getNextException();
-		}
-	}
-
-	private static void freeStmtRs(final Statement stmt, final ResultSet rs) {
-		// free resources
-		if (rs != null) {
-			try { rs.close(); } catch (SQLException e) { /* ignore */ }
-		}
-		if (stmt != null) {
-			try { stmt.close(); } catch (SQLException e) { /* ignore */ }
-		}
-	}
-
-	private static String minimumWidth(int val, int minWidth) {
-		String valstr = Integer.toString(val);
-		int spacesneeded = minWidth - valstr.length();
-		switch (spacesneeded) {
-			case 1: return " " + valstr;
-			case 2: return "  " + valstr;
-			case 3: return "   " + valstr;
-			case 4: return "    " + valstr;
-			case 5: return "     " + valstr;
-			case 6: return "      " + valstr;
-			default: return valstr;
-		}
-	}
-
-
-// ********* below are many 2-dimensional String arrays (all private) containing the data for constructing the validation queries *********
-	// based on data from: https://dev.monetdb.org/hg/MonetDB/file/Jun2020/sql/test/sys-schema/Tests
-
-	// static list of all sys tables with its pkey columns
-	// each entry contains: table_nm, pk_col_nms, from_minor_version
-	// data originally pulled from https://dev.monetdb.org/hg/MonetDB/file/Jun2020/sql/test/sys-schema/Tests/check_PrimaryKey_uniqueness.sql
-	private static final String[][] sys_pkeys = {
-		{"schemas", "id", null},
-		{"_tables", "id", null},
-		{"tables", "id", null},	// is a view
-		{"_columns", "id", null},
-		{"columns", "id", null},	// is a view
-		{"functions", "id", null},
-		{"systemfunctions", "function_id", null},	// has become a view in Apr2019 (11.33.3) and maybe removed in the future as is deprecated
-		{"args", "id", null},
-		{"types", "id", null},
-		{"objects", "id, nr", null},
-		{"keys", "id", null},
-		{"idxs", "id", null},
-		{"triggers", "id", null},
-		{"sequences", "id", null},
-		{"dependency_types", "dependency_type_id", null},
-		{"dependencies", "id, depend_id", null},
-		{"auths", "id", null},
-		{"users", "name", null},
-		{"user_role", "login_id, role_id", null},
-		{"privileges", "obj_id, auth_id, privileges", null},
-		{"querylog_catalog", "id", null},
-		{"querylog_calls", "id", null},
-		{"querylog_history", "id", null},
-		{"optimizers", "name", null},
-		{"environment", "name", null},	// is a view on sys.env()
-		{"db_user_info", "name", null},
-		{"statistics", "column_id", null},
-// old	{"tracelog", "event", null},		-- Error: Profiler not started. This table now (Jun2020) contains only: ticks, stmt
-//		{"storage", "schema, table, column", null},	// is a view on table producing function: storage().
-		{"\"storage\"()", "schema, table, column", null},	// the function "storage"() also lists the storage for system tables
-		{"storagemodelinput", "schema, table, column", null},
-
-		{"rejects", "rowid", "19"},	// querying this view caused problems in versions pre Jul2015, see https://www.monetdb.org/bugzilla/show_bug.cgi?id=3794
-
-		{"keywords", "keyword", "21"},		// introduced in Jul2015 release (11.21.5)
-		{"table_types", "table_type_id", "21"},		// introduced in Jul2015 release (11.21.5)
-
-		{"function_languages", "language_id", "27"},		// introduced in Jul2017 release (11.27.1)
-		{"function_types", "function_type_id", "27"},		// introduced in Jul2017 release (11.27.1)
-		{"index_types", "index_type_id", "27"},		// introduced in Jul2017 release (11.27.1)
-		{"key_types", "key_type_id", "27"},		// introduced in Jul2017 release (11.27.1)
-		{"privilege_codes", "privilege_code_id", "27"},		// introduced in Jul2017 release (11.27.1)
-
-		{"comments", "id", "29"},		// introduced in Mar2018 release (11.29.3)
-		{"ids", "id", "29"},		// introduced in Mar2018 release (11.29.3), it is a view
-		{"var_values", "var_name", "29"},		// var_values is introduced in Mar2018 release (11.29.3), it is a view
-
-		// new views introduced in Apr 2019 feature release (11.33.3)
-//		{"tablestorage", "schema, table", "33"},	// is a view on view storage
-//		{"schemastorage", "schema", "33"},	// is a view on view storage
-//		{"storagemodel", "schema, table, column", null},	// is a view on storagemodelinput
-//		{"tablestoragemodel", "schema, table", null},	// is a view on storagemodelinput
-
-	// new tables introduced in Apr 2019 feature release (11.33.3)
-		{"table_partitions", "id", "33"},
-		{"range_partitions", "table_id, partition_id, minimum", "33"},
-		{"value_partitions", "table_id, partition_id, \"value\"", "33"},
-
-// old	{"queue", "qtag", null},	// queue has changed in Jun2020 (11.37.7), pkey was previously qtag
-		{"queue", "tag", "37"},		// queue has changed in Jun2020 (11.37.7), pkey is now called tag
-// old	{"sessions", "\"user\", login, active", null},	// sessions has changed in Jun2020 (11.37.7), pkey was previously "user", login, active
-		{"sessions", "sessionid", "37"}		// sessions has changed in Jun2020 (11.37.7), pkey is now called sessionid
-	};
-
-	private static final String[][] tmp_pkeys = {
-		{"_tables", "id", null},
-		{"_columns", "id", null},
-		{"objects", "id, nr", null},
-		{"keys", "id", null},
-		{"idxs", "id", null},
-		{"triggers", "id", null}
-	};
-
-	private static final String[][] netcdf_pkeys = {
-		{"netcdf_files", "file_id", null},
-		{"netcdf_attrs", "file_id, att_name", null},	// to be verified if this is correct, maybe also include obj_name
-		{"netcdf_dims", "dim_id, file_id", null},
-		{"netcdf_vars", "var_id, file_id", null},
-		{"netcdf_vardim", "var_id, dim_id, file_id", null}
-	};
-
-	private static final String[][] geom_pkeys = {
-		{"spatial_ref_sys", "srid", null}
-	};
-
-	
-	// static list of all sys tables with its alternate key (unique constraint) columns
-	// each entry contains: table_nm, ak_col_nms, from_minor_version
-	// data originally pulled from https://dev.monetdb.org/hg/MonetDB/file/Jun2020/sql/test/sys-schema/Tests/check_AlternateKey_uniqueness.sql
-	private static final String[][] sys_akeys = {
-		{"schemas", "name", null},
-		{"_tables", "schema_id, name", null},
-		{"tables", "schema_id, name", null},	// is a view
-		{"_columns", "table_id, name", null},
-		{"columns", "table_id, name", null},	// is a view
-		{"_columns", "table_id, number", null},
-		{"columns", "table_id, number", null},	// is a view
-		// The id values from sys.schemas, sys._tables, sys._columns and sys.functions combined must be exclusive (see FK from sys.privileges.obj_id)
-		{"(SELECT id FROM sys.schemas UNION ALL SELECT id FROM sys._tables UNION ALL SELECT id FROM sys._columns UNION ALL SELECT id FROM sys.functions) as T", "T.id", null},
-		{"(SELECT id FROM sys.schemas UNION ALL SELECT id FROM sys.tables UNION ALL SELECT id FROM sys.columns UNION ALL SELECT id FROM sys.functions) as T", "T.id", null},
-		// the next query used to return duplicates for overloaded functions (same function but with different arg names/types), hence it has been extended
-		{"functions f join sys.args a on f.id=a.func_id", "schema_id, f.name, func, mod, language, f.type, side_effect, varres, vararg, a.id", null},
-		{"args", "func_id, name, inout", null},
-		{"types", "schema_id, systemname, sqlname", null},
-		{"objects", "id, name", null},
-		{"keys", "table_id, name", null},
-		{"idxs", "table_id, name", null},
-		{"triggers", "table_id, name", null},
-		{"sequences", "schema_id, name", null},
-		{"dependency_types", "dependency_type_name", null},
-		{"auths", "name", null},		// is this always unique?? is it possible to define a user and a role with the same name?
-		{"optimizers", "def", null},
-
-	// new tables introduced in older release
-		{"table_types", "table_type_name", "21"},
-		{"function_types", "function_type_name", "27"},
-		{"function_languages", "language_name", "27"},
-		{"index_types", "index_type_name", "27"},
-		{"key_types", "key_type_name", "27"},
-		{"privilege_codes", "privilege_code_name", "27"},
-		{"comments", "id", "29"},
-	// new tables introduced in Apr 2019 feature release (11.33.3)
-		{"table_partitions WHERE column_id IS NOT NULL", "table_id, column_id", "33"},	// requires WHERE "column_id" IS NOT NULL
-		{"table_partitions WHERE \"expression\" IS NOT NULL", "table_id, \"expression\"", "33"},	// requires WHERE "expression" IS NOT NULL
-		{"range_partitions", "table_id, partition_id, \"maximum\"", "33"}
-	};
-
-	private static final String[][] tmp_akeys = {
-		{"_tables", "schema_id, name", null},
-		{"_columns", "table_id, name", null},
-		{"_columns", "table_id, number", null},
-		{"objects", "id, name", null},
-		{"keys", "table_id, name", null},
-		{"idxs", "table_id, name", null},
-		{"triggers", "table_id, name", null}
-	};
-
-	private static final String[][] netcdf_akeys = {
-		{"netcdf_files", "location", null}
-	};
-
-	private static final String[][] geom_akeys = {
-		{"spatial_ref_sys", "auth_name, auth_srid, srtext, proj4text", null}
-	};
-
-
-	// static list of all sys tables with its foreign key columns
-	// each entry contains: table_nm, fk_col_nms, ref_col_nms, ref_tbl_nm, from_minor_version
-	// data originally pulled from https://dev.monetdb.org/hg/MonetDB/file/Jun2020/sql/test/sys-schema/Tests/check_ForeignKey_referential_integrity.sql
-	private static final String[][] sys_fkeys = {
-		{"schemas", "authorization", "id", "auths", null},
-		{"schemas", "owner", "id", "auths", null},
-		{"_tables", "schema_id", "id", "schemas", null},
-		{"tables", "schema_id", "id", "schemas", null},
-		{"_tables", "type", "table_type_id", "table_types", "21"},
-		{"tables", "type", "table_type_id", "table_types", "21"},
-		{"_columns", "table_id", "id", "_tables", null},
-		{"columns", "table_id", "id", "tables", null},
-		{"_columns", "type", "sqlname", "types", null},
-		{"columns", "type", "sqlname", "types", null},
-		{"functions", "schema_id", "id", "schemas", null},
-		{"functions", "type", "function_type_id", "function_types", "27"},
-		{"functions", "language", "language_id", "function_languages", "27"},
-		// system functions should refer only to functions in MonetDB system schemas
-		{"functions WHERE system AND ", "schema_id", "id", "schemas WHERE system", null},
-		{"args", "func_id", "id", "functions", null},
-		{"args", "type", "sqlname", "types", null},
-		{"types", "schema_id", "id", "schemas", null},
-	//	{"types WHERE schema_id <> 0 AND ", "schema_id", "id", "schemas", null},	// types with schema_id = 0 should no longer exist
-		{"objects", "id", "id", "ids", "29"},
-		{"ids WHERE obj_type IN ('key', 'index') AND ", "id", "id", "objects", "29"},
-		{"keys", "id", "id", "objects", null},
-		{"keys", "table_id", "id", "_tables", null},
-		{"keys", "table_id", "id", "tables", null},
-		{"keys", "type", "key_type_id", "key_types", "27"},
-		{"keys WHERE rkey <> -1 AND ", "rkey", "id", "keys", null},
-// SELECT * FROM sys.keys WHERE action <> -1 AND action NOT IN (SELECT id FROM sys.?);  -- TODO: find out which action values are valid and what they mean.
-		{"idxs", "id", "id", "objects", null},
-		{"idxs", "table_id", "id", "_tables", null},
-		{"idxs", "table_id", "id", "tables", null},
-		{"idxs", "type", "index_type_id", "index_types", "27"},
-		{"sequences", "schema_id", "id", "schemas", null},
-		{"triggers", "table_id", "id", "_tables", null},
-		{"triggers", "table_id", "id", "tables", null},
-		{"comments", "id", "id", "ids", "29"},
-		{"dependencies", "id", "id", "ids", "29"},
-		{"dependencies", "depend_id", "id", "ids", "29"},
-		{"dependencies", "depend_type", "dependency_type_id", "dependency_types", null},
-		{"dependencies", "id, depend_id, depend_type", "v.id, v.used_by_id, v.depend_type", "dependencies_vw v", "29"},		// dependencies_vw is introduced in Mar2018 release (11.29.3), it is a view
-		{"auths WHERE grantor > 0 AND ", "grantor", "id", "auths", null},
-		{"users", "name", "name", "auths", null},
-		{"users", "default_schema", "id", "schemas", null},
-		{"db_user_info", "name", "name", "auths", null},
-		{"db_user_info", "default_schema", "id", "schemas", null},
-		{"user_role", "login_id", "id", "auths", null},
-		{"user_role", "login_id", "a.id", "auths a WHERE a.name IN (SELECT u.name FROM sys.users u)", null},
-		{"user_role", "role_id", "id", "auths", null},
-		{"user_role", "role_id", "a.id", "auths a WHERE a.name IN (SELECT u.name FROM sys.users u)", null},
-		{"user_role", "role_id", "id", "roles", "29"},		// roles is introduced in Mar2018 release (11.29.3), it is a view
-		{"privileges", "obj_id", "id", "(SELECT id FROM sys.schemas UNION ALL SELECT id FROM sys._tables UNION ALL SELECT id FROM sys._columns UNION ALL SELECT id FROM sys.functions) as t", null},
-		{"privileges", "auth_id", "id", "auths", null},
-		{"privileges WHERE grantor > 0 AND ", "grantor", "id", "auths", null},
-		{"privileges", "privileges", "privilege_code_id", "privilege_codes", "27"},
-		{"querylog_catalog", "owner", "name", "users", null},
-		{"querylog_catalog", "pipe", "name", "optimizers", null},
-		{"querylog_calls", "id", "id", "querylog_catalog", null},
-		{"querylog_history", "id", "id", "querylog_catalog", null},
-		{"querylog_history", "owner", "name", "users", null},
-		{"querylog_history", "pipe", "name", "optimizers", null},
-		{"queue WHERE tag > cast(0 as oid) AND ", "tag", "tag", "queue", null},
-		{"queue WHERE tag > cast(0 as oid) AND ", "tag", "cast(tag as oid)", "queue", null},
-		{"queue", "tag", "cast(tag as oid)", "queue", null},
-		{"queue", "\"username\"", "name", "users", null},
-		{"sessions", "\"username\"", "name", "users", null},
-		{"statistics", "column_id", "id", "(SELECT id FROM sys._columns UNION ALL SELECT id FROM tmp._columns) as c", null},
-		{"statistics", "type", "sqlname", "types", null},
-		{"storage()", "schema", "name", "schemas", null},
-		{"storage()", "table", "name", "(SELECT name FROM sys._tables UNION ALL SELECT name FROM tmp._tables) as t", null},
-		{"storage()", "schema, table", "sname, tname", "(SELECT sch.name as sname, tbl.name as tname FROM sys.schemas AS sch JOIN sys.tables AS tbl ON sch.id = tbl.schema_id) as t", null},
-		{"storage()", "column", "name", "(SELECT name FROM sys._columns UNION ALL SELECT name FROM tmp._columns UNION ALL SELECT name FROM sys.keys UNION ALL SELECT name FROM tmp.keys UNION ALL SELECT name FROM sys.idxs UNION ALL SELECT name FROM tmp.idxs) as c", null},
-		{"storage()", "type", "sqlname", "types", null},
-		{"storage", "schema", "name", "schemas", null},
-		{"storage", "table", "name", "(SELECT name FROM sys._tables UNION ALL SELECT name FROM tmp._tables) as t", null},
-		{"storage", "schema, table", "sname, tname", "(SELECT sch.name as sname, tbl.name as tname FROM sys.schemas AS sch JOIN sys.tables AS tbl ON sch.id = tbl.schema_id) as t", null},
-		{"storage", "column", "name", "(SELECT name FROM sys._columns UNION ALL SELECT name FROM tmp._columns UNION ALL SELECT name FROM sys.keys UNION ALL SELECT name FROM tmp.keys UNION ALL SELECT name FROM sys.idxs UNION ALL SELECT name FROM tmp.idxs) as c", null},
-		{"storage", "type", "sqlname", "types", null},
-		{"storagemodel", "schema", "name", "schemas", null},
-		{"storagemodel", "table", "name", "(SELECT name FROM sys._tables UNION ALL SELECT name FROM tmp._tables) as t", null},
-		{"storagemodel", "schema, table", "sname, tname", "(SELECT sch.name as sname, tbl.name as tname FROM sys.schemas AS sch JOIN sys.tables AS tbl ON sch.id = tbl.schema_id) as t", null},
-		{"storagemodel", "column", "name", "(SELECT name FROM sys._columns UNION ALL SELECT name FROM tmp._columns UNION ALL SELECT name FROM sys.keys UNION ALL SELECT name FROM tmp.keys UNION ALL SELECT name FROM sys.idxs UNION ALL SELECT name FROM tmp.idxs) as c", null},
-		{"storagemodel", "type", "sqlname", "types", null},
-		{"storagemodelinput", "schema", "name", "schemas", null},
-		{"storagemodelinput", "table", "name", "(SELECT name FROM sys._tables UNION ALL SELECT name FROM tmp._tables) as t", null},
-		{"storagemodelinput", "schema, table", "sname, tname", "(SELECT sch.name as sname, tbl.name as tname FROM sys.schemas AS sch JOIN sys.tables AS tbl ON sch.id = tbl.schema_id) as t", null},
-		{"storagemodelinput", "column", "name", "(SELECT name FROM sys._columns UNION ALL SELECT name FROM tmp._columns UNION ALL SELECT name FROM sys.keys UNION ALL SELECT name FROM tmp.keys UNION ALL SELECT name FROM sys.idxs UNION ALL SELECT name FROM tmp.idxs) as c", null},
-		{"storagemodelinput", "type", "sqlname", "types", null},
-		{"tablestoragemodel", "schema", "name", "schemas", null},
-		{"tablestoragemodel", "table", "name", "(SELECT name FROM sys._tables UNION ALL SELECT name FROM tmp._tables) as t", null},
-		{"tablestoragemodel", "schema, table", "sname, tname", "(SELECT sch.name as sname, tbl.name as tname FROM sys.schemas AS sch JOIN sys.tables AS tbl ON sch.id = tbl.schema_id) as t", null},
-	// new tables / views introduced in Apr2019  "33"
-		{"schemastorage", "schema", "name", "schemas", "33"},
-		{"tablestorage", "schema", "name", "schemas", "33"},
-		{"tablestorage", "table", "name", "(SELECT name FROM sys._tables UNION ALL SELECT name FROM tmp._tables) as t", "33"},
-		{"tablestorage", "schema, table", "sname, tname", "(SELECT sch.name as sname, tbl.name as tname FROM sys.schemas AS sch JOIN sys.tables AS tbl ON sch.id = tbl.schema_id) as t", "33"},
-		{"table_partitions", "table_id", "id", "_tables", "33"},
-		{"table_partitions WHERE column_id IS NOT NULL AND ", "column_id", "id", "_columns", "33"},
-		{"range_partitions", "table_id", "id", "_tables", "33"},
-		{"range_partitions", "partition_id", "id", "table_partitions", "33"},
-		{"value_partitions", "table_id", "id", "_tables", "33"},
-		{"value_partitions", "partition_id", "id", "table_partitions", "33"}
-	};
-
-	private static final String[][] tmp_fkeys = {
-		{"_tables", "schema_id", "id", "sys.schemas", null},
-		{"_tables", "type", "table_type_id", "sys.table_types", "21"},
-		{"_columns", "table_id", "id", "_tables", null},
-		{"_columns", "type", "sqlname", "sys.types", null},
-		{"keys", "id", "id", "objects", null},
-		{"keys", "table_id", "id", "_tables", null},
-		{"keys", "type", "key_type_id", "sys.key_types", "27"},
-		{"keys WHERE rkey <> -1 AND ", "rkey", "id", "keys", null},
-// SELECT * FROM tmp.keys WHERE action <> -1 AND action NOT IN (SELECT id FROM tmp.?);  -- TODO: find out which action values are valid and what they mean.
-		{"idxs", "id", "id", "objects", null},
-		{"idxs", "table_id", "id", "_tables", null},
-		{"idxs", "type", "index_type_id", "sys.index_types", "27"},
-		{"objects", "id", "id", "sys.ids", "29"},
-		{"triggers", "table_id", "id", "_tables", null}
-	};
-
-	private static final String[][] netcdf_fkeys = {
-		{"netcdf_attrs", "file_id", "file_id", "netcdf_files", null},
-		{"netcdf_dims", "file_id", "file_id", "netcdf_files", null},
-		{"netcdf_vars", "file_id", "file_id", "netcdf_files", null},
-		{"netcdf_vardim", "file_id", "file_id", "netcdf_files", null},
-		{"netcdf_vardim", "dim_id", "dim_id", "netcdf_dims", null},
-		{"netcdf_vardim", "dim_id, file_id", "dim_id, file_id", "netcdf_dims", null},
-		{"netcdf_vardim", "var_id", "var_id", "netcdf_vars", null},
-		{"netcdf_vardim", "var_id, file_id", "var_id, file_id", "netcdf_vars", null}
-	};
-
-	private static final String[][] geom_fkeys = {
-		{"spatial_ref_sys", "auth_srid", "srid", "spatial_ref_sys", null}
-	};
-
-
-	// static list of all sys tables with its not null constraint columns
-	// each entry contains: table_nm, col_nm, from_minor_version
-	// data originally pulled from https://dev.monetdb.org/hg/MonetDB/file/Jun2020/sql/test/sys-schema/Tests/check_Not_Nullable_columns.sql
-	private static final String[][] sys_notnull = {
-		{"_columns", "id", null},
-		{"_columns", "name", null},
-		{"_columns", "type", null},
-		{"_columns", "type_digits", null},
-		{"_columns", "type_scale", null},
-		{"_columns", "table_id", null},
-		{"_columns", "\"null\"", null},
-		{"_columns", "number", null},
-		{"_tables", "id", null},
-		{"_tables", "name", null},
-		{"_tables", "schema_id", null},
-		{"_tables", "type", null},
-		{"_tables", "system", null},
-		{"_tables", "commit_action", null},
-		{"_tables", "access", null},
-		{"args", "id", null},
-		{"args", "func_id", null},
-		{"args", "name", null},
-		{"args", "type", null},
-		{"args", "type_digits", null},
-		{"args", "type_scale", null},
-		{"args", "inout", null},
-		{"args", "number", null},
-		{"auths", "id", null},
-		{"auths", "name", null},
-		{"auths", "grantor", null},
-		{"db_user_info", "name", null},
-		{"db_user_info", "fullname", null},
-		{"db_user_info", "default_schema", null},
-		{"dependencies", "id", null},
-		{"dependencies", "depend_id", null},
-		{"dependencies", "depend_type", null},
-		{"function_languages", "language_id", "27"},
-		{"function_languages", "language_name", "27"},
-		{"function_types", "function_type_id", "27"},
-		{"function_types", "function_type_name", "27"},
-		{"function_types", "function_type_keyword", "27"},
-		{"functions", "id", null},
-		{"functions", "name", null},
-		{"functions", "func", null},
-		{"functions", "mod", null},
-		{"functions", "language", null},
-		{"functions", "type", null},
-		{"functions", "side_effect", null},
-		{"functions", "varres", null},
-		{"functions", "vararg", null},
-		{"functions", "schema_id", null},
-		{"functions", "system", null},
-		{"idxs", "id", null},
-		{"idxs", "table_id", null},
-		{"idxs", "type", null},
-		{"idxs", "name", null},
-		{"index_types", "index_type_id", "27"},
-		{"index_types", "index_type_name", "27"},
-		{"key_types", "key_type_id", "27"},
-		{"key_types", "key_type_name", "27"},
-		{"keys", "id", null},
-		{"keys", "table_id", null},
-		{"keys", "type", null},
-		{"keys", "name", null},
-		{"keys", "rkey", null},
-		{"keys", "action", null},
-		{"keywords", "keyword", "21"},
-		{"objects", "id", null},
-		{"objects", "name", null},
-		{"objects", "nr", null},
-		{"optimizers", "name", null},
-		{"optimizers", "def", null},
-		{"optimizers", "status", null},
-		{"privilege_codes", "privilege_code_id", "27"},
-		{"privilege_codes", "privilege_code_name", "27"},
-		{"privileges", "obj_id", null},
-		{"privileges", "auth_id", null},
-		{"privileges", "privileges", null},
-		{"privileges", "grantor", null},
-		{"privileges", "grantable", null},
-		{"schemas", "id", null},
-		{"schemas", "name", null},
-		{"schemas", "authorization", null},
-		{"schemas", "owner", null},
-		{"schemas", "system", null},
-		{"sequences", "id", null},
-		{"sequences", "schema_id", null},
-		{"sequences", "name", null},
-		{"sequences", "start", null},
-		{"sequences", "minvalue", null},
-		{"sequences", "maxvalue", null},
-		{"sequences", "increment", null},
-		{"sequences", "cacheinc", null},
-		{"sequences", "cycle", null},
-		{"statistics", "column_id", null},
-		{"statistics", "type", null},
-		{"statistics", "width", null},
-		{"statistics", "stamp", null},
-		{"statistics", "\"sample\"", null},
-		{"statistics", "count", null},
-		{"statistics", "\"unique\"", null},
-		{"statistics", "nils", null},
-		{"statistics", "sorted", null},
-		{"statistics", "revsorted", null},
-		// the table producing function "storage"() also lists the storage for system tables, whereas the view "storage" does not, so use "storage"()
-		{"\"storage\"()", "schema", null},
-		{"\"storage\"()", "table", null},
-		{"\"storage\"()", "column", null},
-		{"\"storage\"()", "type", null},
-		{"\"storage\"()", "mode", null},
-		{"\"storage\"()", "location", null},
-		{"\"storage\"()", "count", null},
-		{"\"storage\"()", "typewidth", null},
-		{"\"storage\"()", "columnsize", null},
-		{"\"storage\"()", "heapsize", null},
-		{"\"storage\"()", "hashes", null},
-		{"\"storage\"()", "phash", null},
-		{"\"storage\"()", "imprints", null},
-		{"\"storage\"()", "orderidx", null},
-		{"storagemodelinput", "schema", null},
-		{"storagemodelinput", "table", null},
-		{"storagemodelinput", "column", null},
-		{"storagemodelinput", "type", null},
-		{"storagemodelinput", "typewidth", null},
-		{"storagemodelinput", "count", null},
-		{"storagemodelinput", "\"distinct\"", null},
-		{"storagemodelinput", "atomwidth", null},
-		{"storagemodelinput", "reference", null},
-		{"storagemodelinput", "sorted", null},
-		{"storagemodelinput", "\"unique\"", null},
-		{"storagemodelinput", "isacolumn", null},
-		{"table_types", "table_type_id", "21"},
-		{"table_types", "table_type_name", "21"},
-		{"tables", "id", null},
-		{"tables", "name", null},
-		{"tables", "schema_id", null},
-		{"tables", "type", null},
-		{"tables", "system", null},
-		{"tables", "commit_action", null},
-		{"tables", "access", null},
-		{"tables", "temporary", null},
-		{"tracelog", "ticks", null},
-		{"tracelog", "stmt", null},
-		{"triggers", "id", null},
-		{"triggers", "name", null},
-		{"triggers", "table_id", null},
-		{"triggers", "time", null},
-		{"triggers", "orientation", null},
-		{"triggers", "event", null},
-		{"triggers", "statement", null},
-		{"types", "id", null},
-		{"types", "systemname", null},
-		{"types", "sqlname", null},
-		{"types", "digits", null},
-		{"types", "scale", null},
-		{"types", "radix", null},
-		{"types", "eclass", null},
-		{"types", "schema_id", null},
-		{"user_role", "login_id", null},
-		{"user_role", "role_id", null},
-		{"users", "name", null},
-		{"users", "fullname", null},
-		{"users", "default_schema", null},
-		{"var_values", "var_name", "29"},
-		{"var_values", "value", "29"},
-	// new tables introduced in Apr 2019 feature release (11.33.3)
-		{"range_partitions", "table_id", "33"},
-		{"range_partitions", "partition_id", "33"},
-		{"range_partitions", "with_nulls", "33"},
-		{"table_partitions", "id", "33"},
-		{"table_partitions", "table_id", "33"},
-		{"table_partitions", "type", "33"},
-		{"value_partitions", "table_id", "33"},
-		{"value_partitions", "partition_id", "33"},
-		{"value_partitions", "value", "33"}		// Can this be null when WITH NULL VALUES is specified?
-	};
-
-	private static final String[][] tmp_notnull = {
-		{"_columns", "id", null},
-		{"_columns", "name", null},
-		{"_columns", "type", null},
-		{"_columns", "type_digits", null},
-		{"_columns", "type_scale", null},
-		{"_columns", "table_id", null},
-		{"_columns", "\"null\"", null},
-		{"_columns", "number", null},
-		{"_tables", "id", null},
-		{"_tables", "name", null},
-		{"_tables", "schema_id", null},
-		{"_tables", "type", null},
-		{"_tables", "system", null},
-		{"_tables", "commit_action", null},
-		{"_tables", "access", null},
-		{"idxs", "id", null},
-		{"idxs", "table_id", null},
-		{"idxs", "type", null},
-		{"idxs", "name", null},
-		{"keys", "id", null},
-		{"keys", "table_id", null},
-		{"keys", "type", null},
-		{"keys", "name", null},
-		{"keys", "rkey", null},
-		{"keys", "action", null},
-		{"objects", "id", null},
-		{"objects", "name", null},
-		{"objects", "nr", null},
-		{"triggers", "id", null},
-		{"triggers", "name", null},
-		{"triggers", "table_id", null},
-		{"triggers", "time", null},
-		{"triggers", "orientation", null},
-		{"triggers", "event", null},
-		{"triggers", "statement", null}
-	};
-
-	private static final String[][] netcdf_notnull = {
-		{"netcdf_files", "file_id", null},
-		{"netcdf_files", "location", null},
-		{"netcdf_dims", "dim_id", null},
-		{"netcdf_dims", "file_id", null},
-		{"netcdf_dims", "name", null},
-		{"netcdf_dims", "length", null},
-		{"netcdf_vars", "var_id", null},
-		{"netcdf_vars", "file_id", null},
-		{"netcdf_vars", "name", null},
-		{"netcdf_vars", "vartype", null},
-		{"netcdf_vardim", "var_id", null},
-		{"netcdf_vardim", "dim_id", null},
-		{"netcdf_vardim", "file_id", null},
-		{"netcdf_vardim", "dimpos", null},
-		{"netcdf_attrs", "obj_name", null},
-		{"netcdf_attrs", "att_name", null},
-		{"netcdf_attrs", "att_type", null},
-		{"netcdf_attrs", "value", null},
-		{"netcdf_attrs", "file_id", null},
-		{"netcdf_attrs", "gr_name", null}
-	};
-
-	private static final String[][] geom_notnull = {
-		{"spatial_ref_sys", "srid", null},
-		{"spatial_ref_sys", "auth_name", null},
-		{"spatial_ref_sys", "auth_srid", null},
-		{"spatial_ref_sys", "srtext", null},
-		{"spatial_ref_sys", "proj4text", null}
-	};
-}

new file mode 100644
--- /dev/null
+++ b/src/main/java/nl/cwi/monetdb/util/MDBvalidator.java
@@ -0,0 +1,1319 @@
+/*
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0.  If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/.
+ *
+ * Copyright 1997 - July 2008 CWI, August 2008 - 2020 MonetDB B.V.
+ */
+
+package nl.cwi.monetdb.util;
+
+import java.sql.Connection;
+import java.sql.DatabaseMetaData;
+import java.sql.ResultSet;
+import java.sql.ResultSetMetaData;
+import java.sql.Statement;
+import java.sql.SQLException;
+import java.sql.Types;
+
+/**
+ * MonetDB Data Integrity Validator class (MDBvalidator) can
+ * a) validate system tables data integrity in system schemas: sys and tmp
+ *    this includes violations of:
+ *		primary key uniqueness
+ *		primary key column(s) not null
+ *		unique constraint uniqueness
+ *		foreign key referential integrity
+ *		column not null
+ *		column maximum length for char/varchar/clob/blob/json/url columns which have max length > 0
+ * b) validate user schema tables & columns data integrity based on available meta data from system tables & system views
+ *		primary key uniqueness
+ *	TODO primary key column(s) not null
+ *		unique constraint uniqueness
+ *	TODO foreign key referential integrity
+ *		column not null
+ *		column maximum length for char/varchar/clob/blob/json/url columns which have max length > 0
+ *
+ * More possible validations for future
+ *		col char/varchar/clob/blob/json/url minimum length (some columns may not be empty, so length >= 1)
+ *		col with sequence (serial/bigserial/autoincrement) in range (0/1/min_value .. max_value)
+ *		col value is valid in domain (date/time/timestamp/json/inet/url/uuid/...)
+ *		col in list checks (some columns may have only certain values which are not stored in a table or view (eg as fk))
+		SELECT * FROM sys.table_partitions WHERE "type" NOT IN (5,6,9,10);	-- 5=By Column Range (1+4), 6=By Expression Range (2+4), 9=By Column Value (1+8), 10=By Expression Value (2+8), see sql_catalog.h #define PARTITION_*.   Note table_partitions is introduced in Apr2019  "33"
+ *		col conditional checks (column is not null when other column is (not) null)
+		-- i.e.: either column_id or expression in sys.table_partitions must be populated
+		SELECT "column_id", "expression", 'Missing either column_id or expression' AS violation, * FROM "sys"."table_partitions" WHERE "column_id" IS NULL AND "expression" IS NULL;
+		SELECT "column_id", "expression", 'column_id and expression may not both be populated. One of them must be NULL' AS violation, * FROM "sys"."table_partitions" WHERE "column_id" IS NOT NULL AND "expression" IS NOT NULL;
+ *
+ * @author Martin van Dinther
+ * @version 0.1
+ */
+
+public final class MDBvalidator {
+	private static final String prg = "MDBvalidator";
+	private Connection con;
+	private int majorversion;
+	private int minorversion;
+
+	private boolean verbose = false;	// set it to true for tracing all generated SQL queries, see validateQuery(qry, ...)
+
+	MDBvalidator(Connection conn) {
+		con = conn;
+	}
+
+/* disabled as it should be called from JdbcClient program
+	public static void main(String[] args) throws Exception {
+		System.out.println(prg + " started with " + args.length + " arguments." + (args.length == 0 ? " Using default JDBC URL !" : ""));
+		// parse input args: connection (JDBC_URL), check systbls (default) or user schema or user db
+
+		String JDBC_URL = (args.length > 0) ? args[0]
+						: "jdbc:monetdb://localhost:50000/demo?user=monetdb&password=monetdb&so_timeout=14000";
+		if (!JDBC_URL.startsWith("jdbc:monetdb://")) {
+			System.out.println("ERROR: Invalid JDBC URL. It does not start with jdbc:monetdb:");
+			return;
+		}
+
+		Connection con = null;
+		try {
+			// make connection to target server
+			con = java.sql.DriverManager.getConnection(JDBC_URL);
+			System.out.println(prg + " connected to MonetDB server");
+			printExceptions(con.getWarnings());
+
+			long start_time = System.currentTimeMillis();
+
+			validateSqlCatalogIntegrity(con);
+			validateSqlNetcdfTablesIntegrity(con);
+			validateSqlGeomTablesIntegrity(con);
+
+			validateSchemaIntegrity(con, "sys");
+			validateDBIntegrity(con);
+
+			long elapsed = System.currentTimeMillis() - start_time;
+			long secs = elapsed /1000;
+			System.out.println("Validation completed in " + secs + "s and " + (elapsed - (secs *1000)) + "ms");
+		} catch (SQLException e) {
+			printExceptions(e);
+		}
+
+		// free resources
+		if (con != null) {
+			try { con.close(); } catch (SQLException e) { /* ignore * /  }
+		}
+	}
+*/
+
+	public static void validateSqlCatalogIntegrity(final Connection conn) {
+		MDBvalidator mdbv = new MDBvalidator(conn);
+		if (mdbv.checkMonetDBVersion()) {
+			mdbv.validateSchema("sys", null, sys_pkeys, sys_akeys, sys_fkeys, sys_notnull, true);
+			mdbv.validateSchema("tmp", null, tmp_pkeys, tmp_akeys, tmp_fkeys, tmp_notnull, true);
+		}
+	}
+
+	public static void validateSqlNetcdfTablesIntegrity(final Connection conn) {
+		MDBvalidator mdbv = new MDBvalidator(conn);
+		if (mdbv.checkMonetDBVersion()) {
+			// determine if the 5 netcdf tables exist in the sys schema
+			if (mdbv.checkTableExists("sys", "netcdf_files")
+			 && mdbv.checkTableExists("sys", "netcdf_dims")
+			 && mdbv.checkTableExists("sys", "netcdf_vars")
+			 && mdbv.checkTableExists("sys", "netcdf_vardim")
+			 && mdbv.checkTableExists("sys", "netcdf_attrs"))
+				mdbv.validateSchema("sys", "netcdf", netcdf_pkeys, netcdf_akeys, netcdf_fkeys, netcdf_notnull, false);
+		}
+	}
+
+	public static void validateSqlGeomTablesIntegrity(final Connection conn) {
+		MDBvalidator mdbv = new MDBvalidator(conn);
+		if (mdbv.checkMonetDBVersion()) {
+			if (mdbv.checkTableExists("sys", "spatial_ref_sys"))	// No need to also test if view sys.geometry_columns exists
+				mdbv.validateSchema("sys", "geom", geom_pkeys, geom_akeys, geom_fkeys, geom_notnull, false);
+		}
+	}
+
+	public static void validateSchemaIntegrity(final Connection conn, final String schema) {
+		MDBvalidator mdbv = new MDBvalidator(conn);
+		if (mdbv.checkSchemaExists(schema))
+			mdbv.validateSchema(schema, null, null, null, null, null, true);
+		else
+			System.out.println("Schema: " + schema + " does not exist in this database.");
+	}
+
+	public static void validateDBIntegrity(final Connection conn) {
+		MDBvalidator mdbv = new MDBvalidator(conn);
+		Statement stmt = mdbv.createStatement("validateDBIntegrity()");
+		if (stmt == null)
+			return;
+
+		boolean hasUserSchemas = false;
+		ResultSet rs = null;
+		try {
+			// retrieve all non-system schemas
+			rs = stmt.executeQuery("SELECT name FROM sys.schemas WHERE NOT system ORDER BY name;");
+			if (rs != null) {
+				// for each user schema do:
+				while (rs.next()) {
+					String schema = rs.getString(1);
+					if (schema != null && !schema.isEmpty()) {
+						hasUserSchemas = true;
+						mdbv.validateSchema(schema, null, null, null, null, null, true);
+					}
+				}
+			}
+		} catch (SQLException e) {
+			printExceptions(e);
+		}
+		freeStmtRs(stmt, rs);
+		if (!hasUserSchemas)
+			System.out.println("No user schemas found in this database.");
+	}
+
+
+	private void validateSchema(
+		final String schema,
+		final String group,
+		final String[][] pkeys,
+		final String[][] ukeys,
+		final String[][] fkeys,
+		final String[][] colnotnull,
+		final boolean checkMaxStr)
+	{
+		boolean is_system_schema = ("sys".equals(schema) || "tmp".equals(schema));
+
+		if (pkeys != null) {
+			validateUniqueness(schema, group, pkeys, "Primary Key uniqueness");
+			validateNotNull(schema, group, pkeys, "Primary Key Not Null");
+		} else {
+			validateUniqueness(schema, true, "Primary Key uniqueness");
+		}
+
+		if (ukeys != null) {
+			validateUniqueness(schema, group, ukeys, "Unique Constraint");
+		} else {
+			validateUniqueness(schema, false, "Unique Constraint");
+		}
+
+		if (fkeys != null) {
+			validateFKs(schema, group, fkeys, "Foreign Key referential integrity");
+		} else {
+			validateFKs(schema, "Foreign Key referential integrity");
+		}
+
+		if (colnotnull != null) {
+			validateNotNull(schema, group, colnotnull, "Not Null");
+		} else {
+			validateNotNull(schema, is_system_schema, "Not Null");
+		}
+
+		if (checkMaxStr)
+			validateMaxCharStrLength(schema, is_system_schema, "Max Character Length");
+	}
+
+	/* validate uniqueness of primary key or uniqueness constraints based on static data array */
+	private void validateUniqueness(
+		final String schema,
+		final String group,
+		final String[][] data,
+		final String checkType)
+	{
+		final int len = data.length;
+		System.out.println("Checking " + minimumWidth(len,6) + (group != null ? " " + group : "") + " tables/keys  in schema " + schema + " for " + checkType + " violations.");
+
+		StringBuilder sb = new StringBuilder(256);	// reusable buffer to compose SQL validation queries
+		sb.append("SELECT COUNT(*) AS duplicates, ");
+		final int qry_len = sb.length();
+		String tbl;
+		String keycols;
+		for (int i = 0; i < len; i++) {
+			if (isValidVersion(data[i][2])) {
+				tbl = data[i][0];
+				keycols = data[i][1];
+				// reuse the StringBuilder by cleaning it partial
+				sb.setLength(qry_len);
+				sb.append(keycols).append(" FROM ");
+				if (!tbl.startsWith("(")) {	// when tbl starts with a ( it is a unioned table set which we cannot prefix with a schema name qualifier
+					sb.append(schema).append('.');
+				}
+				sb.append(tbl)
+				.append(" GROUP BY ").append(keycols)
+				.append(" HAVING COUNT(*) > 1;");
+				validateQuery(sb.toString(), schema, tbl, keycols, checkType);
+			}
+		}
+	}
+
+	/* validate uniqueness of primary key or uniqueness constraints based on dynamic retrieved system data from sys.keys */
+	private void validateUniqueness(
+		final String schema,
+		final boolean pkey,
+		final String checkType)
+	{
+		Statement stmt = createStatement("validateUniqueness()");
+		if (stmt == null)
+			return;
+
+		// fetch the primary or unique key info from the MonetDB system tables
+		StringBuilder sb = new StringBuilder(400);
+		sb.append(" FROM sys.keys k JOIN sys.tables t ON k.table_id = t.id JOIN sys.schemas s ON t.schema_id = s.id"
+				+ " WHERE k.type = ").append(pkey ? 0 : 1)	// 0 = primary keys, 1 = unique keys
+			.append(" and s.name = '").append(schema).append("'");
+		String qry = sb.toString();
+		final int count = runCountQuery(qry);
+		System.out.println("Checking " + minimumWidth(count,6) + " keys         in schema " + schema + " for " + checkType + " violations.");
+
+		ResultSet rs = null;
+		try {
+			sb.setLength(0);	// empty previous usage of sb
+			// fetch the primary or unique key info including columns from the MonetDB system tables
+			sb.append("SELECT s.name as sch_nm, t.name as tbl_nm, k.name as key_nm, o.name as col_nm, o.nr")
+			.append(" FROM sys.keys k JOIN sys.objects o ON k.id = o.id JOIN sys.tables t ON k.table_id = t.id JOIN sys.schemas s ON t.schema_id = s.id"
+				+ " WHERE k.type = ").append(pkey ? 0 : 1)	// 0 = primary keys, 1 = unique keys
+			.append(" and s.name = '").append(schema).append("'")
+			.append(" ORDER BY t.name, k.name, o.nr;");
+			qry = sb.toString();
+			rs = stmt.executeQuery(qry);
+			if (rs != null) {
+				String sch = null, tbl, key, col;
+				String prv_tbl = null, prv_key = null, keycols = null;
+				sb.setLength(0);	// empty previous usage of sb
+				sb.append("SELECT COUNT(*) AS duplicates, ");
+				final int qry_len = sb.length();
+				while (rs.next()) {
+					// retrieve meta data
+					sch = rs.getString(1);
+					tbl = rs.getString(2);
+					key = rs.getString(3);
+					col = rs.getString(4);
+					if (prv_tbl == null)
+						prv_tbl = tbl;
+					if (prv_key == null)
+						prv_key = key;
+					if (tbl.equals(prv_tbl) && key.equals(prv_key)) {
+						if (keycols == null)
+							keycols = "\"" + col + "\"";
+						else
+							keycols = keycols + ", \"" + col + "\"";
+					} else {
+						// compose validation query for the previous retrieved key columns
+						// reuse the StringBuilder by cleaning it partial
+						sb.setLength(qry_len);
+						sb.append(keycols)
+						.append(" FROM \"").append(sch).append("\".\"").append(prv_tbl).append("\"")
+						.append(" GROUP BY ").append(keycols)
+						.append(" HAVING COUNT(*) > 1;");
+						validateQuery(sb.toString(), sch, prv_tbl, keycols, checkType);
+						prv_tbl = tbl;
+						prv_key = key;
+						keycols = "\"" + col + "\"";
+					}
+				}
+				if (sch != null && prv_tbl != null && keycols != null) {
+					// compose validation query for the last retrieved key
+					// reuse the StringBuilder by cleaning it partial
+					sb.setLength(qry_len);
+					sb.append(keycols)
+					.append(" FROM \"").append(sch).append("\".\"").append(prv_tbl).append("\"")
+					.append(" GROUP BY ").append(keycols)
+					.append(" HAVING COUNT(*) > 1;");
+					validateQuery(sb.toString(), sch, prv_tbl, keycols, checkType);
+				}
+			}
+		} catch (SQLException e) {
+			System.err.println("Failed to execute query: " + qry);
+			printExceptions(e);
+		}
+		freeStmtRs(stmt, rs);
+	}
+
+	/* validate foreign key constraints based on static data array */
+	private void validateFKs(
+		final String schema,
+		final String group,
+		final String[][] data,
+		final String checkType)
+	{
+		final int len = data.length;
+		System.out.println("Checking " + minimumWidth(len,6) + (group != null ? " " + group : "") + " foreign keys in schema " + schema + " for " + checkType + " violations.");
+
+		StringBuilder sb = new StringBuilder(400);	// reusable buffer to compose SQL validation queries
+		sb.append("SELECT ");
+		final int qry_len = sb.length();
+		String tbl;
+		String cols;
+		String ref_tbl;
+		String ref_cols;
+		for (int i = 0; i < len; i++) {
+			if (isValidVersion(data[i][4])) {
+				tbl = data[i][0];
+				cols = data[i][1];
+				ref_cols = data[i][2];
+				ref_tbl = data[i][3];
+				// reuse the StringBuilder by cleaning it partial
+				sb.setLength(qry_len);
+				sb.append(cols).append(", * FROM ").append(schema).append('.').append(tbl);
+				if (!tbl.contains(" WHERE "))
+					sb.append(" WHERE ");
+				sb.append('(').append(cols).append(") NOT IN (SELECT ").append(ref_cols).append(" FROM ");
+				if (!ref_tbl.contains("."))
+					sb.append(schema).append('.');
+				sb.append(ref_tbl).append(");");
+				validateQuery(sb.toString(), schema, tbl, cols, checkType);
+			}
+		}
+	}
+
+	/* validate foreign key constraints based on dynamic retrieved system data from sys.keys */
+	private void validateFKs(
+		final String schema,
+		final String checkType)
+	{
+		Statement stmt = createStatement("validateFKs()");
+		if (stmt == null)
+			return;
+
+		// fetch the foreign key info from the MonetDB system tables
+		StringBuilder sb = new StringBuilder(400);
+		sb.append(" FROM sys.keys k JOIN sys.tables t ON k.table_id = t.id JOIN sys.schemas s ON t.schema_id = s.id"
+				+ " WHERE k.type = 2")	// 2 = foreign keys
+			.append(" and s.name = '").append(schema).append("'");
+		String qry = sb.toString();
+		final int count = runCountQuery(qry);
+		System.out.println("Checking " + minimumWidth(count,6) + " foreign keys in schema " + schema + " for " + checkType + " violations.");
+
+		ResultSet rs = null;
+		// TODO: finish FK validation implementation
+
+		freeStmtRs(stmt, rs);
+	}
+
+	/* validate NOT NULL constraints based on static data array */
+	private void validateNotNull(
+		final String schema,
+		final String group,
+		final String[][] data,
+		final String checkType)
+	{
+		final int len = data.length;
+		System.out.println("Checking " + minimumWidth(len,6) + (group != null ? " " + group : "") + " columns      in schema " + schema + " for " + checkType + " violations.");
+
+		StringBuilder sb = new StringBuilder(256);	// reusable buffer to compose SQL validation queries
+		sb.append("SELECT ");
+		final int qry_len = sb.length();
+		String tbl;
+		String col;
+		boolean multicolumn = false;
+		StringBuilder isNullCond = new StringBuilder(80);
+		for (int i = 0; i < len; i++) {
+			if (isValidVersion(data[i][2])) {
+				tbl = data[i][0];
+				col = data[i][1];
+				multicolumn = col.contains(", ");	// some pkeys consist of multiple columns
+				isNullCond.setLength(0);	// empty previous content
+				if (multicolumn) {
+					String[] cols = col.split(", ");
+					for (int c = 0; c < cols.length; c++) {
+						if (c > 0) {
+							isNullCond.append(" OR ");
+						}
+						isNullCond.append(cols[c]).append(" IS NULL");
+					}
+				} else {
+					isNullCond.append(col).append(" IS NULL");
+				}
+				// reuse the StringBuilder by cleaning it partial
+				sb.setLength(qry_len);
+				sb.append(col)
+				.append(", * FROM ").append(schema).append('.').append(tbl)
+				.append(" WHERE ").append(isNullCond).append(';');
+				validateQuery(sb.toString(), schema, tbl, col, checkType);
+			}
+		}
+	}
+
+	/* validate NOT NULL constraints based on dynamic retrieved system data from sys.columns */
+	private void validateNotNull(
+		final String schema,
+		final boolean system,
+		final String checkType)
+	{
+		Statement stmt = createStatement("validateNotNull()");
+		if (stmt == null)
+			return;
+
+		// fetch the NOT NULL info from the MonetDB system tables as those are leading for user tables (but not system tables)
+		StringBuilder sb = new StringBuilder(400);
+		sb.append(" from sys.columns c join sys.tables t on c.table_id = t.id join sys.schemas s on t.schema_id = s.id"
+				+ " where t.type in (0, 10, 1, 11) and c.\"null\" = false"	// t.type 0 = TABLE, 10 = SYSTEM TABLE, 1 = VIEW, 11 = SYSTEM VIEW
+				+ " and t.system = ").append(system)
+			.append(" and s.name = '").append(schema).append("'");
+		String qry = sb.toString();
+		final int count = runCountQuery(qry);
+		System.out.println("Checking " + minimumWidth(count,6) + " columns      in schema " + schema + " for " + checkType + " violations.");
+
+		ResultSet rs = null;
+		try {
+			sb.setLength(0);	// empty previous usage of sb
+			sb.append("SELECT s.name as sch_nm, t.name as tbl_nm, c.name as col_nm")	// , t.type, t.system, c.type, c.type_digits
+			.append(qry).append(" ORDER BY s.name, t.name, c.name;");
+			qry = sb.toString();
+			rs = stmt.executeQuery(qry);
+			if (rs != null) {
+				String sch, tbl, col;
+				while (rs.next()) {
+					// retrieve meta data
+					sch = rs.getString(1);
+					tbl = rs.getString(2);
+					col = rs.getString(3);
+					// compose validation query for this specific column
+					sb.setLength(0);	// empty previous usage of sb
+					sb.append("SELECT '").append(sch).append('.').append(tbl).append('.').append(col).append("' as full_col_nm, *")
+					.append(" FROM \"").append(sch).append("\".\"").append(tbl).append("\"")
+					.append(" WHERE \"").append(col).append("\" IS NULL;");
+					validateQuery(sb.toString(), sch, tbl, col, checkType);
+				}
+			}
+		} catch (SQLException e) {
+			System.err.println("Failed to execute query: " + qry);
+			printExceptions(e);
+		}
+		freeStmtRs(stmt, rs);
+	}
+
+	/* validate Maximum (Var)Char(LOB) Length constraints based on dynamic retrieved system data from sys.columns */
+	private void validateMaxCharStrLength(
+		final String schema,
+		final boolean system,
+		final String checkType)
+	{
+		Statement stmt = createStatement("validateMaxCharStrLength()");
+		if (stmt == null)
+			return;
+
+		// fetch the max char str len info from the MonetDB system tables as those are leading
+		StringBuilder sb = new StringBuilder(400);
+		sb.append(" from sys.columns c join sys.tables t on c.table_id = t.id join sys.schemas s on t.schema_id = s.id"
+				+ " where t.type in (0, 10, 1, 11)"	// t.type 0 = TABLE, 10 = SYSTEM TABLE, 1 = VIEW, 11 = SYSTEM VIEW
+				+ " and c.type_digits >= 1"		// only when a positive max length is specified
+				+ " and t.system = ").append(system)
+			.append(" and c.type in ('varchar','char','clob','json','url','blob')")	// only for variable character/bytes data type columns
+			.append(" and s.name = '").append(schema).append("'");
+		String qry = sb.toString();
+		final int count = runCountQuery(qry);
+		System.out.println("Checking " + minimumWidth(count,6) + " columns      in schema " + schema + " for " + checkType + " violations.");
+
+		ResultSet rs = null;
+		try {
+			sb.setLength(0);	// empty previous usage of sb
+			sb.append("SELECT s.name as sch_nm, t.name as tbl_nm, c.name as col_nm, c.type_digits")	// , t.type, t.system, c.type
+			.append(qry).append(" ORDER BY s.name, t.name, c.name, c.type_digits;");
+			qry = sb.toString();
+			rs = stmt.executeQuery(qry);
+			if (rs != null) {
+				long max_len = 0;
+				String sch, tbl, col;
+				while (rs.next()) {
+					// retrieve meta data
+					sch = rs.getString(1);
+					tbl = rs.getString(2);
+					col = rs.getString(3);
+					max_len = rs.getLong(4);
+					// compose validation query for this specific column
+					sb.setLength(0);	// empty previous usage of sb
+					sb.append("SELECT '").append(sch).append('.').append(tbl).append('.').append(col).append("' as full_col_nm, ")
+					.append(max_len).append(" as max_allowed_length, ")
+					.append("length(\"").append(col).append("\") as data_length, ")
+					.append("\"").append(col).append("\" as data_value")
+					.append(" FROM \"").append(sch).append("\".\"").append(tbl).append("\"")
+					.append(" WHERE \"").append(col).append("\" IS NOT NULL AND length(\"").append(col).append("\") > ").append(max_len);
+					validateQuery(sb.toString(), sch, tbl, col, checkType);
+				}
+			}
+		} catch (SQLException e) {
+			System.err.println("Failed to execute query: " + qry);
+			printExceptions(e);
+		}
+		freeStmtRs(stmt, rs);
+	}
+
+
+	/* Run a validation query.
+	 * It should result in no rows returned.
+	 * When rows are returned those are the ones that contain violations.
+	 * Retrieve them and convert the results (currently first 16 only) into a (large) violation string
+	 * Log/Print the violation.
+	 */
+	private void validateQuery(
+		final String qry,
+		final String sch,
+		final String tbl,
+		final String cols,
+		final String checkType)
+	{
+		Statement stmt = createStatement("validateQuery()");
+		if (stmt == null)
+			return;
+
+		ResultSet rs = null;
+		try {
+			if (verbose) {
+				System.out.println(qry);
+			}
+			rs = stmt.executeQuery(qry);
+			if (rs != null) {
+				final ResultSetMetaData rsmd = rs.getMetaData();
+				final int nr_cols = rsmd.getColumnCount();
+				final StringBuilder sb = new StringBuilder(1024);
+				final int maxprintrows = 16;
+				int row = 0;
+				String val;
+				int tp;
+				while (rs.next()) {
+					// query returns found violations
+					row++;
+					if (row == 1) {
+						// print result header once
+						for (int i = 1; i <= nr_cols; i++) {
+							sb.append((i > 1) ? ", " : "\t");
+							sb.append(rsmd.getColumnLabel(i));
+						}
+						sb.append('\n');
+					}
+					if (row <= maxprintrows) { // print only the first n rows
+						// retrieve row data
+						for (int i = 1; i <= nr_cols; i++) {
+							sb.append((i > 1) ? ", " : "\t");
+							val = rs.getString(i);
+							if (val == null || rs.wasNull()) {
+								sb.append("null");
+							} else {
+								tp = rsmd.getColumnType(i);	// this method is very fast, so no need to cache it outside the loop
+								if (tp == Types.VARCHAR || tp == Types.CHAR || tp == Types.CLOB || tp == Types.BLOB) {
+									sb.append('"').append(val).append('"');
+								} else {
+									sb.append(val);
+								}
+							}
+						}
+						sb.append('\n');
+					}
+				}
+				if (row > 0) {
+					if (row > maxprintrows) {
+						sb.append("...\n");
+						sb.append("Listed only first ").append(maxprintrows).append(" violations of ").append(row).append(" found!\n");
+					}
+					logViolations(checkType, sch, tbl, cols, qry, sb.toString());
+				}
+			}
+		} catch (SQLException e) {
+			System.err.println("Failed to execute query: " + qry);
+			printExceptions(e);
+		}
+		freeStmtRs(stmt, rs);
+	}
+
+	private int runCountQuery(final String from_qry) {
+		Statement stmt = createStatement("runCountQuery()");
+		if (stmt == null)
+			return 0;
+
+		ResultSet rs = null;
+		int count = 0;
+		try {
+			rs = stmt.executeQuery("SELECT COUNT(*) " + from_qry);
+			if (rs != null) {
+				if (rs.next()) {
+					// retrieve count data
+					count = rs.getInt(1);
+				}
+			}
+		} catch (SQLException e) {
+			System.err.println("Failed to execute SELECT COUNT(*) " + from_qry);
+			printExceptions(e);
+		}
+		freeStmtRs(stmt, rs);
+		return count;
+	}
+
+	private Statement createStatement(final String method) {
+		try {
+			return con.createStatement();
+		} catch (SQLException e) {
+			System.err.print("Failed to create Statement in " + method);
+			printExceptions(e);
+		}
+		return null;
+	}
+
+	private boolean checkMonetDBVersion() {
+		if (majorversion == 0 && minorversion == 0) {
+			// we haven't fetched them before.
+			try {
+				// retrieve server version numbers (major and minor). These are needed to filter out version specific validations
+				DatabaseMetaData dbmd = con.getMetaData();
+				if (dbmd != null) {
+					// System.out.println("MonetDB server version " + dbmd.getDatabaseProductVersion());
+					majorversion = dbmd.getDatabaseMajorVersion();
+					minorversion = dbmd.getDatabaseMinorVersion();
+				}
+			} catch (SQLException e) {
+				printExceptions(e);
+			}
+		}
+		// validate majorversion (should be 11) and minorversion (should be >= 19) (from Jul2015 (11.19.15))
+		if (majorversion < 11 || (majorversion == 11 && minorversion < 19)) {
+			System.out.println("Warning: this MonetDB server is too old for " + prg + ". Please upgrade MonetDB server.");
+			return false;
+		}
+		return true;
+	}
+
+	private boolean isValidVersion(final String version) {
+		if (version == null)
+			return true;	// when no version string is supplied it is valid by default
+
+		try {
+			int v = Integer.parseInt(version);
+			return minorversion >= v;
+		} catch (NumberFormatException e) {
+			System.out.println("Failed to parse version string '" + version + "' as an integer number.");
+		}
+		return false;
+	}
+
+	private boolean checkSchemaExists(final String schema) {
+		Statement stmt = createStatement("checkSchemaExists()");
+		if (stmt == null)
+			return false;
+
+		String sql = "SELECT name FROM sys.schemas WHERE name = '" + schema + "';";
+		ResultSet rs = null;
+		boolean ret = false;
+		try {
+			rs = stmt.executeQuery(sql);
+			if (rs != null) {
+				if (rs.next()) {
+					if (schema != null && schema.equals(rs.getString(1)))
+						ret = true;
+				}
+			}
+		} catch (SQLException e) {
+			System.err.println("Failed to execute " + sql);
+			printExceptions(e);
+		}
+		freeStmtRs(stmt, rs);
+		return ret;
+	}
+
+	private boolean checkTableExists(final String schema, final String table) {
+		Statement stmt = createStatement("checkTableExists()");
+		if (stmt == null)
+			return false;
+
+		String sql = "SELECT s.name, t.name FROM sys.tables t JOIN sys.schemas s ON t.schema_id = s.id WHERE t.name = '" + table + "' AND s.name = '" + schema + "';";
+		ResultSet rs = null;
+		boolean ret = false;
+		try {
+			rs = stmt.executeQuery(sql);
+			if (rs != null) {
+				if (rs.next()) {
+					if (schema != null && schema.equals(rs.getString(1))
+					 && table  != null && table.equals(rs.getString(2)) )
+						ret = true;
+				}
+			}
+		} catch (SQLException e) {
+			System.err.println("Failed to execute " + sql);
+			printExceptions(e);
+		}
+		freeStmtRs(stmt, rs);
+		return ret;
+	}
+
+	private void logViolations(
+		final String checkType,
+		final String schema,
+		final String table,
+		final String columns,
+		final String query,
+		final String violations)
+	{
+		StringBuilder sb = new StringBuilder(2048);
+		sb.append(checkType).append(" violation(s) found in \"")
+		  .append(schema).append("\".\"").append(table).append("\".\"").append(columns).append("\":\n")
+		  .append(violations)
+		  .append("Found using query: ").append(query).append("\n");
+		System.out.println(sb.toString());
+	}
+
+	private static void printExceptions(SQLException se) {
+		while (se != null) {
+			System.err.println(se.getSQLState() + " " + se.getMessage());
+			se = se.getNextException();
+		}
+	}
+
+	private static void freeStmtRs(final Statement stmt, final ResultSet rs) {
+		// free resources
+		if (rs != null) {
+			try { rs.close(); } catch (SQLException e) { /* ignore */ }
+		}
+		if (stmt != null) {
+			try { stmt.close(); } catch (SQLException e) { /* ignore */ }
+		}
+	}
+
+	private static String minimumWidth(int val, int minWidth) {
+		String valstr = Integer.toString(val);
+		int spacesneeded = minWidth - valstr.length();
+		switch (spacesneeded) {
+			case 1: return " " + valstr;
+			case 2: return "  " + valstr;
+			case 3: return "   " + valstr;
+			case 4: return "    " + valstr;
+			case 5: return "     " + valstr;
+			case 6: return "      " + valstr;
+			default: return valstr;
+		}
+	}
+
+
+// ********* below are many 2-dimensional String arrays (all private) containing the data for constructing the validation queries *********
+	// based on data from: https://dev.monetdb.org/hg/MonetDB/file/Jun2020/sql/test/sys-schema/Tests
+
+	// static list of all sys tables with its pkey columns
+	// each entry contains: table_nm, pk_col_nms, from_minor_version
+	// data originally pulled from https://dev.monetdb.org/hg/MonetDB/file/Jun2020/sql/test/sys-schema/Tests/check_PrimaryKey_uniqueness.sql
+	private static final String[][] sys_pkeys = {
+		{"schemas", "id", null},
+		{"_tables", "id", null},
+		{"tables", "id", null},	// is a view
+		{"_columns", "id", null},
+		{"columns", "id", null},	// is a view
+		{"functions", "id", null},
+		{"systemfunctions", "function_id", null},	// has become a view in Apr2019 (11.33.3) and maybe removed in the future as is deprecated
+		{"args", "id", null},
+		{"types", "id", null},
+		{"objects", "id, nr", null},
+		{"keys", "id", null},
+		{"idxs", "id", null},
+		{"triggers", "id", null},
+		{"sequences", "id", null},
+		{"dependency_types", "dependency_type_id", null},
+		{"dependencies", "id, depend_id", null},
+		{"auths", "id", null},
+		{"users", "name", null},
+		{"user_role", "login_id, role_id", null},
+		{"privileges", "obj_id, auth_id, privileges", null},
+		{"querylog_catalog", "id", null},
+		{"querylog_calls", "id", null},
+		{"querylog_history", "id", null},
+		{"optimizers", "name", null},
+		{"environment", "name", null},	// is a view on sys.env()
+		{"db_user_info", "name", null},
+		{"statistics", "column_id", null},
+// old	{"tracelog", "event", null},		-- Error: Profiler not started. This table now (Jun2020) contains only: ticks, stmt
+//		{"storage", "schema, table, column", null},	// is a view on table producing function: storage().
+		{"\"storage\"()", "schema, table, column", null},	// the function "storage"() also lists the storage for system tables
+		{"storagemodelinput", "schema, table, column", null},
+
+		{"rejects", "rowid", "19"},	// querying this view caused problems in versions pre Jul2015, see https://www.monetdb.org/bugzilla/show_bug.cgi?id=3794
+
+		{"keywords", "keyword", "21"},		// introduced in Jul2015 release (11.21.5)
+		{"table_types", "table_type_id", "21"},		// introduced in Jul2015 release (11.21.5)
+
+		{"function_languages", "language_id", "27"},		// introduced in Jul2017 release (11.27.1)
+		{"function_types", "function_type_id", "27"},		// introduced in Jul2017 release (11.27.1)
+		{"index_types", "index_type_id", "27"},		// introduced in Jul2017 release (11.27.1)
+		{"key_types", "key_type_id", "27"},		// introduced in Jul2017 release (11.27.1)
+		{"privilege_codes", "privilege_code_id", "27"},		// introduced in Jul2017 release (11.27.1)
+
+		{"comments", "id", "29"},		// introduced in Mar2018 release (11.29.3)
+		{"ids", "id", "29"},		// introduced in Mar2018 release (11.29.3), it is a view
+		{"var_values", "var_name", "29"},		// var_values is introduced in Mar2018 release (11.29.3), it is a view
+
+		// new views introduced in Apr 2019 feature release (11.33.3)
+//		{"tablestorage", "schema, table", "33"},	// is a view on view storage
+//		{"schemastorage", "schema", "33"},	// is a view on view storage
+//		{"storagemodel", "schema, table, column", null},	// is a view on storagemodelinput
+//		{"tablestoragemodel", "schema, table", null},	// is a view on storagemodelinput
+
+	// new tables introduced in Apr 2019 feature release (11.33.3)
+		{"table_partitions", "id", "33"},
+		{"range_partitions", "table_id, partition_id, minimum", "33"},
+		{"value_partitions", "table_id, partition_id, \"value\"", "33"},
+
+// old	{"queue", "qtag", null},	// queue has changed in Jun2020 (11.37.7), pkey was previously qtag
+		{"queue", "tag", "37"},		// queue has changed in Jun2020 (11.37.7), pkey is now called tag
+// old	{"sessions", "\"user\", login, active", null},	// sessions has changed in Jun2020 (11.37.7), pkey was previously "user", login, active
+		{"sessions", "sessionid", "37"}		// sessions has changed in Jun2020 (11.37.7), pkey is now called sessionid
+	};
+
+	private static final String[][] tmp_pkeys = {
+		{"_tables", "id", null},
+		{"_columns", "id", null},
+		{"objects", "id, nr", null},
+		{"keys", "id", null},
+		{"idxs", "id", null},
+		{"triggers", "id", null}
+	};
+
+	private static final String[][] netcdf_pkeys = {
+		{"netcdf_files", "file_id", null},
+		{"netcdf_attrs", "file_id, att_name", null},	// to be verified if this is correct, maybe also include obj_name
+		{"netcdf_dims", "dim_id, file_id", null},
+		{"netcdf_vars", "var_id, file_id", null},
+		{"netcdf_vardim", "var_id, dim_id, file_id", null}
+	};
+
+	private static final String[][] geom_pkeys = {
+		{"spatial_ref_sys", "srid", null}
+	};
+
+
+	// static list of all sys tables with its alternate key (unique constraint) columns
+	// each entry contains: table_nm, ak_col_nms, from_minor_version
+	// data originally pulled from https://dev.monetdb.org/hg/MonetDB/file/Jun2020/sql/test/sys-schema/Tests/check_AlternateKey_uniqueness.sql
+	private static final String[][] sys_akeys = {
+		{"schemas", "name", null},
+		{"_tables", "schema_id, name", null},
+		{"tables", "schema_id, name", null},	// is a view
+		{"_columns", "table_id, name", null},
+		{"columns", "table_id, name", null},	// is a view
+		{"_columns", "table_id, number", null},
+		{"columns", "table_id, number", null},	// is a view
+		// The id values from sys.schemas, sys._tables, sys._columns and sys.functions combined must be exclusive (see FK from sys.privileges.obj_id)
+		{"(SELECT id FROM sys.schemas UNION ALL SELECT id FROM sys._tables UNION ALL SELECT id FROM sys._columns UNION ALL SELECT id FROM sys.functions) as T", "T.id", null},
+		{"(SELECT id FROM sys.schemas UNION ALL SELECT id FROM sys.tables UNION ALL SELECT id FROM sys.columns UNION ALL SELECT id FROM sys.functions) as T", "T.id", null},
+		// the next query used to return duplicates for overloaded functions (same function but with different arg names/types), hence it has been extended
+		{"functions f join sys.args a on f.id=a.func_id", "schema_id, f.name, func, mod, language, f.type, side_effect, varres, vararg, a.id", null},
+		{"args", "func_id, name, inout", null},
+		{"types", "schema_id, systemname, sqlname", null},
+		{"objects", "id, name", null},
+		{"keys", "table_id, name", null},
+		{"idxs", "table_id, name", null},
+		{"triggers", "table_id, name", null},
+		{"sequences", "schema_id, name", null},
+		{"dependency_types", "dependency_type_name", null},
+		{"auths", "name", null},		// is this always unique?? is it possible to define a user and a role with the same name?
+		{"optimizers", "def", null},
+
+	// new tables introduced in older release
+		{"table_types", "table_type_name", "21"},
+		{"function_types", "function_type_name", "27"},
+		{"function_languages", "language_name", "27"},
+		{"index_types", "index_type_name", "27"},
+		{"key_types", "key_type_name", "27"},
+		{"privilege_codes", "privilege_code_name", "27"},
+		{"comments", "id", "29"},
+	// new tables introduced in Apr 2019 feature release (11.33.3)
+		{"table_partitions WHERE column_id IS NOT NULL", "table_id, column_id", "33"},	// requires WHERE "column_id" IS NOT NULL
+		{"table_partitions WHERE \"expression\" IS NOT NULL", "table_id, \"expression\"", "33"},	// requires WHERE "expression" IS NOT NULL
+		{"range_partitions", "table_id, partition_id, \"maximum\"", "33"}
+	};
+
+	private static final String[][] tmp_akeys = {
+		{"_tables", "schema_id, name", null},
+		{"_columns", "table_id, name", null},
+		{"_columns", "table_id, number", null},
+		{"objects", "id, name", null},
+		{"keys", "table_id, name", null},
+		{"idxs", "table_id, name", null},
+		{"triggers", "table_id, name", null}
+	};
+
+	private static final String[][] netcdf_akeys = {
+		{"netcdf_files", "location", null}
+	};
+
+	private static final String[][] geom_akeys = {
+		{"spatial_ref_sys", "auth_name, auth_srid, srtext, proj4text", null}
+	};
+
+
+	// static list of all sys tables with its foreign key columns
+	// each entry contains: table_nm, fk_col_nms, ref_col_nms, ref_tbl_nm, from_minor_version
+	// data originally pulled from https://dev.monetdb.org/hg/MonetDB/file/Jun2020/sql/test/sys-schema/Tests/check_ForeignKey_referential_integrity.sql
+	private static final String[][] sys_fkeys = {
+		{"schemas", "authorization", "id", "auths", null},
+		{"schemas", "owner", "id", "auths", null},
+		{"_tables", "schema_id", "id", "schemas", null},
+		{"tables", "schema_id", "id", "schemas", null},
+		{"_tables", "type", "table_type_id", "table_types", "21"},
+		{"tables", "type", "table_type_id", "table_types", "21"},
+		{"_columns", "table_id", "id", "_tables", null},
+		{"columns", "table_id", "id", "tables", null},
+		{"_columns", "type", "sqlname", "types", null},
+		{"columns", "type", "sqlname", "types", null},
+		{"functions", "schema_id", "id", "schemas", null},
+		{"functions", "type", "function_type_id", "function_types", "27"},
+		{"functions", "language", "language_id", "function_languages", "27"},
+		// system functions should refer only to functions in MonetDB system schemas
+		{"functions WHERE system AND ", "schema_id", "id", "schemas WHERE system", null},
+		{"args", "func_id", "id", "functions", null},
+		{"args", "type", "sqlname", "types", null},
+		{"types", "schema_id", "id", "schemas", null},
+	//	{"types WHERE schema_id <> 0 AND ", "schema_id", "id", "schemas", null},	// types with schema_id = 0 should no longer exist
+		{"objects", "id", "id", "ids", "29"},
+		{"ids WHERE obj_type IN ('key', 'index') AND ", "id", "id", "objects", "29"},
+		{"keys", "id", "id", "objects", null},
+		{"keys", "table_id", "id", "_tables", null},
+		{"keys", "table_id", "id", "tables", null},
+		{"keys", "type", "key_type_id", "key_types", "27"},
+		{"keys WHERE rkey <> -1 AND ", "rkey", "id", "keys", null},
+// SELECT * FROM sys.keys WHERE action <> -1 AND action NOT IN (SELECT id FROM sys.?);  -- TODO: find out which action values are valid and what they mean.
+		{"idxs", "id", "id", "objects", null},
+		{"idxs", "table_id", "id", "_tables", null},
+		{"idxs", "table_id", "id", "tables", null},
+		{"idxs", "type", "index_type_id", "index_types", "27"},
+		{"sequences", "schema_id", "id", "schemas", null},
+		{"triggers", "table_id", "id", "_tables", null},
+		{"triggers", "table_id", "id", "tables", null},
+		{"comments", "id", "id", "ids", "29"},
+		{"dependencies", "id", "id", "ids", "29"},
+		{"dependencies", "depend_id", "id", "ids", "29"},
+		{"dependencies", "depend_type", "dependency_type_id", "dependency_types", null},
+		{"dependencies", "id, depend_id, depend_type", "v.id, v.used_by_id, v.depend_type", "dependencies_vw v", "29"},		// dependencies_vw is introduced in Mar2018 release (11.29.3), it is a view
+		{"auths WHERE grantor > 0 AND ", "grantor", "id", "auths", null},
+		{"users", "name", "name", "auths", null},
+		{"users", "default_schema", "id", "schemas", null},
+		{"db_user_info", "name", "name", "auths", null},
+		{"db_user_info", "default_schema", "id", "schemas", null},
+		{"user_role", "login_id", "id", "auths", null},
+		{"user_role", "login_id", "a.id", "auths a WHERE a.name IN (SELECT u.name FROM sys.users u)", null},
+		{"user_role", "role_id", "id", "auths", null},
+		{"user_role", "role_id", "a.id", "auths a WHERE a.name IN (SELECT u.name FROM sys.users u)", null},
+		{"user_role", "role_id", "id", "roles", "29"},		// roles is introduced in Mar2018 release (11.29.3), it is a view
+		{"privileges", "obj_id", "id", "(SELECT id FROM sys.schemas UNION ALL SELECT id FROM sys._tables UNION ALL SELECT id FROM sys._columns UNION ALL SELECT id FROM sys.functions) as t", null},
+		{"privileges", "auth_id", "id", "auths", null},
+		{"privileges WHERE grantor > 0 AND ", "grantor", "id", "auths", null},
+		{"privileges", "privileges", "privilege_code_id", "privilege_codes", "27"},
+		{"querylog_catalog", "owner", "name", "users", null},
+		{"querylog_catalog", "pipe", "name", "optimizers", null},
+		{"querylog_calls", "id", "id", "querylog_catalog", null},
+		{"querylog_history", "id", "id", "querylog_catalog", null},
+		{"querylog_history", "owner", "name", "users", null},
+		{"querylog_history", "pipe", "name", "optimizers", null},
+		{"queue WHERE tag > cast(0 as oid) AND ", "tag", "tag", "queue", null},
+		{"queue WHERE tag > cast(0 as oid) AND ", "tag", "cast(tag as oid)", "queue", null},
+		{"queue", "tag", "cast(tag as oid)", "queue", null},
+		{"queue", "\"username\"", "name", "users", null},
+		{"sessions", "\"username\"", "name", "users", null},
+		{"statistics", "column_id", "id", "(SELECT id FROM sys._columns UNION ALL SELECT id FROM tmp._columns) as c", null},
+		{"statistics", "type", "sqlname", "types", null},
+		{"storage()", "schema", "name", "schemas", null},
+		{"storage()", "table", "name", "(SELECT name FROM sys._tables UNION ALL SELECT name FROM tmp._tables) as t", null},
+		{"storage()", "schema, table", "sname, tname", "(SELECT sch.name as sname, tbl.name as tname FROM sys.schemas AS sch JOIN sys.tables AS tbl ON sch.id = tbl.schema_id) as t", null},
+		{"storage()", "column", "name", "(SELECT name FROM sys._columns UNION ALL SELECT name FROM tmp._columns UNION ALL SELECT name FROM sys.keys UNION ALL SELECT name FROM tmp.keys UNION ALL SELECT name FROM sys.idxs UNION ALL SELECT name FROM tmp.idxs) as c", null},
+		{"storage()", "type", "sqlname", "types", null},
+		{"storage", "schema", "name", "schemas", null},
+		{"storage", "table", "name", "(SELECT name FROM sys._tables UNION ALL SELECT name FROM tmp._tables) as t", null},
+		{"storage", "schema, table", "sname, tname", "(SELECT sch.name as sname, tbl.name as tname FROM sys.schemas AS sch JOIN sys.tables AS tbl ON sch.id = tbl.schema_id) as t", null},
+		{"storage", "column", "name", "(SELECT name FROM sys._columns UNION ALL SELECT name FROM tmp._columns UNION ALL SELECT name FROM sys.keys UNION ALL SELECT name FROM tmp.keys UNION ALL SELECT name FROM sys.idxs UNION ALL SELECT name FROM tmp.idxs) as c", null},
+		{"storage", "type", "sqlname", "types", null},
+		{"storagemodel", "schema", "name", "schemas", null},
+		{"storagemodel", "table", "name", "(SELECT name FROM sys._tables UNION ALL SELECT name FROM tmp._tables) as t", null},
+		{"storagemodel", "schema, table", "sname, tname", "(SELECT sch.name as sname, tbl.name as tname FROM sys.schemas AS sch JOIN sys.tables AS tbl ON sch.id = tbl.schema_id) as t", null},
+		{"storagemodel", "column", "name", "(SELECT name FROM sys._columns UNION ALL SELECT name FROM tmp._columns UNION ALL SELECT name FROM sys.keys UNION ALL SELECT name FROM tmp.keys UNION ALL SELECT name FROM sys.idxs UNION ALL SELECT name FROM tmp.idxs) as c", null},
+		{"storagemodel", "type", "sqlname", "types", null},
+		{"storagemodelinput", "schema", "name", "schemas", null},
+		{"storagemodelinput", "table", "name", "(SELECT name FROM sys._tables UNION ALL SELECT name FROM tmp._tables) as t", null},
+		{"storagemodelinput", "schema, table", "sname, tname", "(SELECT sch.name as sname, tbl.name as tname FROM sys.schemas AS sch JOIN sys.tables AS tbl ON sch.id = tbl.schema_id) as t", null},
+		{"storagemodelinput", "column", "name", "(SELECT name FROM sys._columns UNION ALL SELECT name FROM tmp._columns UNION ALL SELECT name FROM sys.keys UNION ALL SELECT name FROM tmp.keys UNION ALL SELECT name FROM sys.idxs UNION ALL SELECT name FROM tmp.idxs) as c", null},
+		{"storagemodelinput", "type", "sqlname", "types", null},
+		{"tablestoragemodel", "schema", "name", "schemas", null},
+		{"tablestoragemodel", "table", "name", "(SELECT name FROM sys._tables UNION ALL SELECT name FROM tmp._tables) as t", null},
+		{"tablestoragemodel", "schema, table", "sname, tname", "(SELECT sch.name as sname, tbl.name as tname FROM sys.schemas AS sch JOIN sys.tables AS tbl ON sch.id = tbl.schema_id) as t", null},
+	// new tables / views introduced in Apr2019  "33"
+		{"schemastorage", "schema", "name", "schemas", "33"},
+		{"tablestorage", "schema", "name", "schemas", "33"},
+		{"tablestorage", "table", "name", "(SELECT name FROM sys._tables UNION ALL SELECT name FROM tmp._tables) as t", "33"},
+		{"tablestorage", "schema, table", "sname, tname", "(SELECT sch.name as sname, tbl.name as tname FROM sys.schemas AS sch JOIN sys.tables AS tbl ON sch.id = tbl.schema_id) as t", "33"},
+		{"table_partitions", "table_id", "id", "_tables", "33"},
+		{"table_partitions WHERE column_id IS NOT NULL AND ", "column_id", "id", "_columns", "33"},
+		{"range_partitions", "table_id", "id", "_tables", "33"},
+		{"range_partitions", "partition_id", "id", "table_partitions", "33"},
+		{"value_partitions", "table_id", "id", "_tables", "33"},
+		{"value_partitions", "partition_id", "id", "table_partitions", "33"}
+	};
+
+	private static final String[][] tmp_fkeys = {
+		{"_tables", "schema_id", "id", "sys.schemas", null},
+		{"_tables", "type", "table_type_id", "sys.table_types", "21"},
+		{"_columns", "table_id", "id", "_tables", null},
+		{"_columns", "type", "sqlname", "sys.types", null},
+		{"keys", "id", "id", "objects", null},
+		{"keys", "table_id", "id", "_tables", null},
+		{"keys", "type", "key_type_id", "sys.key_types", "27"},
+		{"keys WHERE rkey <> -1 AND ", "rkey", "id", "keys", null},
+// SELECT * FROM tmp.keys WHERE action <> -1 AND action NOT IN (SELECT id FROM tmp.?);  -- TODO: find out which action values are valid and what they mean.
+		{"idxs", "id", "id", "objects", null},
+		{"idxs", "table_id", "id", "_tables", null},
+		{"idxs", "type", "index_type_id", "sys.index_types", "27"},
+		{"objects", "id", "id", "sys.ids", "29"},
+		{"triggers", "table_id", "id", "_tables", null}
+	};
+
+	private static final String[][] netcdf_fkeys = {
+		{"netcdf_attrs", "file_id", "file_id", "netcdf_files", null},
+		{"netcdf_dims", "file_id", "file_id", "netcdf_files", null},
+		{"netcdf_vars", "file_id", "file_id", "netcdf_files", null},
+		{"netcdf_vardim", "file_id", "file_id", "netcdf_files", null},
+		{"netcdf_vardim", "dim_id", "dim_id", "netcdf_dims", null},
+		{"netcdf_vardim", "dim_id, file_id", "dim_id, file_id", "netcdf_dims", null},
+		{"netcdf_vardim", "var_id", "var_id", "netcdf_vars", null},
+		{"netcdf_vardim", "var_id, file_id", "var_id, file_id", "netcdf_vars", null}
+	};
+
+	private static final String[][] geom_fkeys = {
+		{"spatial_ref_sys", "auth_srid", "srid", "spatial_ref_sys", null}
+	};
+
+
+	// static list of all sys tables with its not null constraint columns
+	// each entry contains: table_nm, col_nm, from_minor_version
+	// data originally pulled from https://dev.monetdb.org/hg/MonetDB/file/Jun2020/sql/test/sys-schema/Tests/check_Not_Nullable_columns.sql
+	private static final String[][] sys_notnull = {
+		{"_columns", "id", null},
+		{"_columns", "name", null},
+		{"_columns", "type", null},
+		{"_columns", "type_digits", null},
+		{"_columns", "type_scale", null},
+		{"_columns", "table_id", null},
+		{"_columns", "\"null\"", null},
+		{"_columns", "number", null},
+		{"_tables", "id", null},
+		{"_tables", "name", null},
+		{"_tables", "schema_id", null},
+		{"_tables", "type", null},
+		{"_tables", "system", null},
+		{"_tables", "commit_action", null},
+		{"_tables", "access", null},
+		{"args", "id", null},
+		{"args", "func_id", null},
+		{"args", "name", null},
+		{"args", "type", null},
+		{"args", "type_digits", null},
+		{"args", "type_scale", null},
+		{"args", "inout", null},
+		{"args", "number", null},
+		{"auths", "id", null},
+		{"auths", "name", null},
+		{"auths", "grantor", null},
+		{"db_user_info", "name", null},
+		{"db_user_info", "fullname", null},
+		{"db_user_info", "default_schema", null},
+		{"dependencies", "id", null},
+		{"dependencies", "depend_id", null},
+		{"dependencies", "depend_type", null},
+		{"function_languages", "language_id", "27"},
+		{"function_languages", "language_name", "27"},
+		{"function_types", "function_type_id", "27"},
+		{"function_types", "function_type_name", "27"},
+		{"function_types", "function_type_keyword", "27"},
+		{"functions", "id", null},
+		{"functions", "name", null},
+		{"functions", "func", null},
+		{"functions", "mod", null},
+		{"functions", "language", null},
+		{"functions", "type", null},
+		{"functions", "side_effect", null},
+		{"functions", "varres", null},
+		{"functions", "vararg", null},
+		{"functions", "schema_id", null},
+		{"functions", "system", null},
+		{"idxs", "id", null},
+		{"idxs", "table_id", null},
+		{"idxs", "type", null},
+		{"idxs", "name", null},
+		{"index_types", "index_type_id", "27"},
+		{"index_types", "index_type_name", "27"},
+		{"key_types", "key_type_id", "27"},
+		{"key_types", "key_type_name", "27"},
+		{"keys", "id", null},
+		{"keys", "table_id", null},
+		{"keys", "type", null},
+		{"keys", "name", null},
+		{"keys", "rkey", null},
+		{"keys", "action", null},
+		{"keywords", "keyword", "21"},
+		{"objects", "id", null},
+		{"objects", "name", null},
+		{"objects", "nr", null},
+		{"optimizers", "name", null},
+		{"optimizers", "def", null},
+		{"optimizers", "status", null},
+		{"privilege_codes", "privilege_code_id", "27"},
+		{"privilege_codes", "privilege_code_name", "27"},
+		{"privileges", "obj_id", null},
+		{"privileges", "auth_id", null},
+		{"privileges", "privileges", null},
+		{"privileges", "grantor", null},
+		{"privileges", "grantable", null},
+		{"schemas", "id", null},
+		{"schemas", "name", null},
+		{"schemas", "authorization", null},
+		{"schemas", "owner", null},
+		{"schemas", "system", null},
+		{"sequences", "id", null},
+		{"sequences", "schema_id", null},
+		{"sequences", "name", null},
+		{"sequences", "start", null},
+		{"sequences", "minvalue", null},
+		{"sequences", "maxvalue", null},
+		{"sequences", "increment", null},
+		{"sequences", "cacheinc", null},
+		{"sequences", "cycle", null},
+		{"statistics", "column_id", null},
+		{"statistics", "type", null},
+		{"statistics", "width", null},
+		{"statistics", "stamp", null},
+		{"statistics", "\"sample\"", null},
+		{"statistics", "count", null},
+		{"statistics", "\"unique\"", null},
+		{"statistics", "nils", null},
+		{"statistics", "sorted", null},
+		{"statistics", "revsorted", null},
+		// the table producing function "storage"() also lists the storage for system tables, whereas the view "storage" does not, so use "storage"()
+		{"\"storage\"()", "schema", null},
+		{"\"storage\"()", "table", null},
+		{"\"storage\"()", "column", null},
+		{"\"storage\"()", "type", null},
+		{"\"storage\"()", "mode", null},
+		{"\"storage\"()", "location", null},
+		{"\"storage\"()", "count", null},
+		{"\"storage\"()", "typewidth", null},
+		{"\"storage\"()", "columnsize", null},
+		{"\"storage\"()", "heapsize", null},
+		{"\"storage\"()", "hashes", null},
+		{"\"storage\"()", "phash", null},
+		{"\"storage\"()", "imprints", null},
+		{"\"storage\"()", "orderidx", null},
+		{"storagemodelinput", "schema", null},
+		{"storagemodelinput", "table", null},
+		{"storagemodelinput", "column", null},
+		{"storagemodelinput", "type", null},
+		{"storagemodelinput", "typewidth", null},
+		{"storagemodelinput", "count", null},
+		{"storagemodelinput", "\"distinct\"", null},
+		{"storagemodelinput", "atomwidth", null},
+		{"storagemodelinput", "reference", null},
+		{"storagemodelinput", "sorted", null},
+		{"storagemodelinput", "\"unique\"", null},
+		{"storagemodelinput", "isacolumn", null},
+		{"table_types", "table_type_id", "21"},
+		{"table_types", "table_type_name", "21"},
+		{"tables", "id", null},
+		{"tables", "name", null},
+		{"tables", "schema_id", null},
+		{"tables", "type", null},
+		{"tables", "system", null},
+		{"tables", "commit_action", null},
+		{"tables", "access", null},
+		{"tables", "temporary", null},
+		{"tracelog", "ticks", null},
+		{"tracelog", "stmt", null},
+		{"triggers", "id", null},
+		{"triggers", "name", null},
+		{"triggers", "table_id", null},
+		{"triggers", "time", null},
+		{"triggers", "orientation", null},
+		{"triggers", "event", null},
+		{"triggers", "statement", null},
+		{"types", "id", null},
+		{"types", "systemname", null},
+		{"types", "sqlname", null},
+		{"types", "digits", null},
+		{"types", "scale", null},
+		{"types", "radix", null},
+		{"types", "eclass", null},
+		{"types", "schema_id", null},
+		{"user_role", "login_id", null},
+		{"user_role", "role_id", null},
+		{"users", "name", null},
+		{"users", "fullname", null},
+		{"users", "default_schema", null},
+		{"var_values", "var_name", "29"},
+		{"var_values", "value", "29"},
+	// new tables introduced in Apr 2019 feature release (11.33.3)
+		{"range_partitions", "table_id", "33"},
+		{"range_partitions", "partition_id", "33"},
+		{"range_partitions", "with_nulls", "33"},
+		{"table_partitions", "id", "33"},
+		{"table_partitions", "table_id", "33"},
+		{"table_partitions", "type", "33"},
+		{"value_partitions", "table_id", "33"},
+		{"value_partitions", "partition_id", "33"},
+		{"value_partitions", "value", "33"}		// Can this be null when WITH NULL VALUES is specified?
+	};
+
+	private static final String[][] tmp_notnull = {
+		{"_columns", "id", null},
+		{"_columns", "name", null},
+		{"_columns", "type", null},
+		{"_columns", "type_digits", null},
+		{"_columns", "type_scale", null},
+		{"_columns", "table_id", null},
+		{"_columns", "\"null\"", null},
+		{"_columns", "number", null},
+		{"_tables", "id", null},
+		{"_tables", "name", null},
+		{"_tables", "schema_id", null},
+		{"_tables", "type", null},
+		{"_tables", "system", null},
+		{"_tables", "commit_action", null},
+		{"_tables", "access", null},
+		{"idxs", "id", null},
+		{"idxs", "table_id", null},
+		{"idxs", "type", null},
+		{"idxs", "name", null},
+		{"keys", "id", null},
+		{"keys", "table_id", null},
+		{"keys", "type", null},
+		{"keys", "name", null},
+		{"keys", "rkey", null},
+		{"keys", "action", null},
+		{"objects", "id", null},
+		{"objects", "name", null},
+		{"objects", "nr", null},
+		{"triggers", "id", null},
+		{"triggers", "name", null},
+		{"triggers", "table_id", null},
+		{"triggers", "time", null},
+		{"triggers", "orientation", null},
+		{"triggers", "event", null},
+		{"triggers", "statement", null}
+	};
+
+	private static final String[][] netcdf_notnull = {
+		{"netcdf_files", "file_id", null},
+		{"netcdf_files", "location", null},
+		{"netcdf_dims", "dim_id", null},
+		{"netcdf_dims", "file_id", null},
+		{"netcdf_dims", "name", null},
+		{"netcdf_dims", "length", null},
+		{"netcdf_vars", "var_id", null},
+		{"netcdf_vars", "file_id", null},
+		{"netcdf_vars", "name", null},
+		{"netcdf_vars", "vartype", null},
+		{"netcdf_vardim", "var_id", null},
+		{"netcdf_vardim", "dim_id", null},
+		{"netcdf_vardim", "file_id", null},
+		{"netcdf_vardim", "dimpos", null},
+		{"netcdf_attrs", "obj_name", null},
+		{"netcdf_attrs", "att_name", null},
+		{"netcdf_attrs", "att_type", null},
+		{"netcdf_attrs", "value", null},
+		{"netcdf_attrs", "file_id", null},
+		{"netcdf_attrs", "gr_name", null}
+	};
+
+	private static final String[][] geom_notnull = {
+		{"spatial_ref_sys", "srid", null},
+		{"spatial_ref_sys", "auth_name", null},
+		{"spatial_ref_sys", "auth_srid", null},
+		{"spatial_ref_sys", "srtext", null},
+		{"spatial_ref_sys", "proj4text", null}
+	};
+}