2. The database query system of claim 1 wherein said QAES includes: a storage system for maintaining state information about the current state of a database query; and a query expert logic system specifying to said QAUI said selectable sets by analyzing said state information maintained in said storage system and said conceptual information stored by said conceptual layer manager.
2. The database query system of claim 1 wherein said QAES includes: a storage system for maintaining state information about the current state of a database query; and a query expert logic system specifying to said QAUI said selectable sets by analyzing said state information maintained in said storage system and said conceptual information stored by said conceptual layer manager. 11. The system of claim 2 wherein said query expert logic system excludes from said selectable column set for any selected one of said tables any numeric column for which, if in said current state of said database query an aggregate column operation is applied to another column based on said selected table or based on another table having a one-to-one relationship with said selected table.