Pragmatics and semantics of NQL, a descriptive query language for network databases

摘要

In this paper we describe a new query language for databases of network type. The language may be classified as descriptive because queries are formulated with the help of powerful predicates at the level of logical data structures. Predicates are adopted to basic forms of link-based and value-based relationships between objects in a network database. They can be nested and combined in such a way that even complex queries can be posed without explicitly using object variables. Semantics of the language is defined by algorithms which transform queries into set-theoretical expressions. The generated expressions can be interpreted over suitable states of databases.