1. In a data processing system, a computer memory tables structure for an object-oriented data model having multiple categories arranged in a hierarchial structure wherein a supercategory is defined having a sub-category, said supercategory having an attribute associated therewith such that attribute values exist for said supercategory and for said sub-category, said computer memory tables structure comprising: multiple computer memory tables separate from but associated with said multiple categories of said object-oriented data model, said multiple computer memory tables retaining said attribute values of said attribute associated with said supercategory, a first memory table being associated with said supercategory for retaining attribute values for said supercategory of said attribute and a second memory table being associated with said sub-category for retaining attribute values for said sub-category of said attribute associated with said supercategory; and a set of unique level-relative indices assigned to said supercategory and said sub-category for accessing said associated multiple computer memory tables, a first level-relative index of said set of level-relative indices being assigned to said supercategory for accessing said first memory table and a second level-relative index of said set of level-relative indices being assigned to said supercategory's sub-category for accessing said second memory table.