A query language for conceptual models and specification languages of the ''entity-relationship'' type

A query language ERQL, which, by the author's intention, is as natural for conceptual models and specification languages of the ''entity-relationship'' type (ER) as the SQL and QUEL query languages are natural for relational data models, is introduced. A language of the local manipulation with entities and relations is determined; it is also natural for ER-models and ER-relations, but on the level of local fragments (neighborhoods) of a net of ''entities-relationships.'' The essential features of the ER-models and ER-languages are formulated in the form of a model of ''entities-relationships'' on which the suggested languages are based.