Hi, thx for all your kind answers. I also find this feature is actually well documented in: http://monetdb.cwi.nl/MonetDB/Version4/Documentation/monet/index.html As deprecated at website, i have never paid attention to these staffs. For those who use MonetDB/XQuery, that may really helpful, at least to be noticed the existence of these documentations. Old problems solved and new questions appear. The mention XML-files flat.xml and deep.xml are send with this mail. Both file have the some content but different structure. flat.xml with less levels and deep.xml with more levels. * Q1: XPath/XQuery will be translated in MIL-Expressions, is the translation deterministic? I mean, can this happen that the same input of XPath/XQuery o will be translated into different MIL-Expressions at different times? o This question seems more related with operation( // , self-or-descendant). * Q2: How should i consider execution cost of XPath? o I.E 1: doc(\"flat.xml\")//entry[@rdn='uid=user.301'] + like one single stair-case-join? + Test result: Need *less *time for execution o I.E 2: doc(\"flat.xml\")/dsml/directory-entries/entry[@rdn='uid=user.301'] + like some nested normal selections? + Test result: Need *more *time for execution * Q3: Is that possible to get translated MIL-Expressions of XPath/XQuery? * Q4: About design of XML. Is there any trade-off-rules, that should be considers with structure design of XML. o For small XML less levels will achieve better performance? o For big XML more levels will achieve better performance? o Test result with flat.xml and deep.xml: ( The difference i found, any explanations? ) + from deep.xml: [ "1000000016_vx_hsh_nid", "int", "oid", 1726, 0, "clean", "load", "pers", 0, 1 ] + from flat.xml: [ "1000000017_vx_hsh_nid", "int", "oid", 825, 0, "clean", "load", "pers", 0, 1 ] So far get so much confused points, hope some experts can give me a hint. Best regards, Chaojing -- ------------------------------------------------------------------------------------------------------------------------------------------ Email: chaojing.yang@gmail.com Blog: http://goethe-ist-taoist.blogspot.com/ §1 Ich widerspreche der Nutzung oder Übermittlung meiner Daten für Werbezwecke oder sowie andere unbefugte Verwendungszwecke. (§ 28 Abs. 4 BDSG=Bundesdatenschutzgesetz). §2 Durch die Datenübertragung bzw. Kommunikation per E-Mail liegt ein Verstoß gegen das BDSG vor, da ihre Daten insoweit nicht ausreichend geschützt sind. Ich bitte Sie daher, mir schriftlich zu bestätigen, dass Sie mit dem Verstoß gegen das BDSG einverstanden sind und keine Schadensersatzanspräche bzw. Unterlassungsanspräche mir gegenüber geltend machen. §3 Der Inhalt dieser Nachricht ist vertraulich und nur für den oben angegebenen Empfänger bestimmt.