Monet way of handling string columns

Hello, I have recently started looking into Monetdb and want to contribute to it. My complete focus is on string columns as numeric data can already be processed with maximum speed. I know it uses BATs to store every single column, but I read some where that it uses dictionary for string columns. How is it actually using dictionary? And are there any other special handling techniques for strings? When a query like 'contains' comes, how will monet handle that? I found there is no inverted index in monet to deal queries like this. (Please tell a rough model of how query execution is done incase of string columns) Hope this forum gives me some insight of what's happening during string column processing. Thanks in advance, -Mitra