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This paper presents a simple approach for extending the relational system INGRES into one supporting a semantic data model it describe a DBMS consisting of (i) a user-friendly front-end, supporting the GEM semantic data model and query language under the UNIX time-sharing system, and (ii) a dedicated back-end processor providing efficient support for database transactions, concurrency control and recovery GEM extends the relational model to support the notions of entities with surrogates, the relationships of aggregation and generalization, null values and set-valued attributes, and provides simple extensions of QUEL to handle these new constructs in this proposed implementation of GEM, the relational database processor IDM 500 by Britton-Lee is used as the back-end machine
Tsur⋆ et al. (Sun,) studied this question.