The week-from-dateTime() function extracts the amount of weeks from a DateTime attribute so it can be used to compare to a value. Values range from 1 to 53 (Which values belong to which week will depend on the database implementation)
//Logging.Log[week-from-dateTime(DateAttribute) = 2]
This query returns all Logs where the amount of weeks in DateAttribute is 2, for example 2011-01-13.