Beschreibung:
GEM (an acronym for General Entity Manipulator) is a general-purpose query and update language for the DSIS data model, which is a semantic data model of the Entity-Relationship type. GEM is designed as an easy-to-use extension of the relational language QUEL, providing support for the notions of entities with surrogates, aggregation, generalization, null values, and set-valued attributes.