Queries in network databases are usually processed by navigation. In this paper, queries are classified according to the network structures to be retrieved to process the queries (so‐called query schemas) and the correspondence of navigational capability, the classes of network queries, and the classes of relational queries are discussed. Simple queries are those whose answers are obtained by selection and projection of connections of records. They are divided into tree queries and cyclic queries according to the cyclicity of their query schemas. Simple queries are generalized to join queries whose answers are obtained from the Cartesian product of connections of records. Basic navigation, which produces only connections of records, can process almost all the tree simple queries and queries in some class of tree join queries. Navigation with facility to compare records can process all simple queries including cyclic queries and some class of join queries. If navigation can use variables to compare with the records' values, all simple and join queries can be processed. Natural join queries in the relational model which do not include lossy join are simple queries in the network model. Most queries including the class of relational complete ones can be processed by navigation.
All Science Journal Classification (ASJC) codes
- Theoretical Computer Science
- Information Systems
- Hardware and Architecture
- Computational Theory and Mathematics