Paper Info
Title
Horn clauses and the fixpoint query hierarchy
Abstract
A logic program consists of a set of Horn clauses, and can be used to express a query on relational data bases. It is shown that logic programs express precisely the queries in YE+ (the set of queries representable by a fixpoint applied to a positive existential query). Queries expressible by logic programs are thus not first order queries in general; nor are all the first order queries expressible as logic programs. A way of adding the negation operator to logic programs is suggested. The resulting set of clausal queries equals FP, the set of first order queries closed under fixpoints (as well as ¬, ∨, 3).
Year
DOI
Venue
1982
10.1145/588111.588137
PODS
Keywords
Field
DocType
relational data base,horn clause,order query,clausal query,positive existential query,queries representable,fixpoint query hierarchy,queries expressible,negation operator,logic program,first order,prolog,query language,relational data
Conjunctive query,Query language,Programming language,Horn clause,Negation,Relational database,Computer science,Theoretical computer science,Prolog,Fixed point,Logic programming
Conference
ISBN
Citations 
PageRank 
0-89791-070-2
33
73.25
References 
Authors
16
2
Name
Order
Citations
PageRank
Ashok K. Chandra131161215.02
David Harel297031953.76