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The Computer Journal 1990 33(6):535-546; doi:10.1093/comjnl/33.6.535
© 1990 by British Computer Society
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Designing SQUIRREL: an extended SQL for a deductive database system

K. G. Waugh *, M. H. Williams *, Q. Kong *, S. Salvini * and G. Chen *

Department of Computer Science, Heriot-Watt University, 79 Grassmarket, Edinburgh, EH1 2HJ, UK

One of the problems facing the designers of a deductive database is that of the choice of query language. The deductive database model is seem as a natural progression from the relational model; the query language should reflect this. This paper reports the decisions taken while designing an extended form of SQL, called SQUIRREL, as the query language for a Prolog-based deductive database. The extensions relate to the inclusion of both rules and incomplete information in the query language and result in changes to the data definition, data manipulation and query languages of SQL. The extensions were constrained by the desire to retain the existing SQL texture in the new language while introducing concepts such as rules, rule manipulation and incomplete information which are alien to the relational philosophy. The language we describe is being used as the interface language for an implementation of a deductive database which will run on a version of Prolog developed to handle database applications.

Received May 1989. revised December 1989.

* Department of Computer Science, Heriot-Watt University, 79 Grassmarket, Edinburgh, EH1 2HJ


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