Data structuring with virtual sets

摘要

Two new data structuring constructs for DBTG-oriented data base systems are introduced: the virtual set and the virtual N : M set. These constructs necessitate few changes in a DDL and require no additional DML commands. Without causing increases in storage and processing costs, these constructs reduce programming effort, enhance the degree of data independence, and offer greater flexibility from the standpoints of subschema and privacy specifications.