Before this patch, when showing content tab squirell makes such a query: "SELECT tbl.* FROM table tbl"... This was altered by usage of TableColumnDefinition. A IDataTypeComponent is requested to provide a column to be selected. This gives something like this: "SELECT tbl.column1,tbl.column2" and so on. With this ability custom data tapes can implement "lazy loading". For example hitting a production database that stores postgis geometries causes a UI to freeze for the time of geometries (few MB each!) to be downloaded. Using this new mechanism TypeComponent can do something like: "SELECT st_summary(tbl.geometry) FROM..." or something similar for other data types.