RELATIONAL COMPLETENESS OF DATA BASE SUBLANGUAGES

TLDR

A growing diversity of languages is expected for querying and updating databases. The paper aims to establish a theoretical framework to assess the completeness of selection capabilities in a data sublanguage, independent of its host language. The authors define relational algebra and calculus and present an algorithm to transform any calculus expression into an equivalent algebraic form. The authors argue that calculus-oriented sublanguages are preferable for optimal search and highly discriminating authorization schemes. RJ 987 Hl7041, March 6, 1972, Computer Sciences.

Abstract

In the near future, we can expect a great variety of languages to be proposed for interrogating and updating data bases. This paper attempts to provide a theoretical basis which may be used to determine how complete a selection capability is provided in a proposed data sublanguage independently of any host language in which the sublanguage may be embedded. A relational algebra and a relational calculus are defined. Then, an algorithm is presented for reducing an arbitrary relation-defining expression (based on the calculus) into a semantically equivalent expression of the relational algebra. Finally, some opinions are stated regarding the relative merits of calculusoriented versus algebra-oriented data sublanguages from the standpoint of optimal search and highly discriminating authorization schemes. RJ 987 Hl7041) March 6, 1972 Computer Sciences