Denotational semantics of query languages

摘要

A denotational semantics approach to formal description of query languages is proposed. It allows us to equip most database models (relational, hierarchical, network, semantic and so on) with powerful query languages possessing clear, formal and precise semantics. It avoids semantic anomalies induced by other approaches and it is immediately directed towards implementation. The paper discusses semantic aspects of key concepts related to query languages: database instances, states and semantic domains related to database queries, operators occurring in queries, transitive closures, and implementation issues. The presentation is illustrated by examples in NETUL, a query/manipulation language for network databases, based on the proposed approach.