Linearisability on datalog programs

  • Authors:
  • Foto Afrati;Manolis Gergatsoulis;Francesca Toni

  • Affiliations:
  • Department of Electrical and Computing Engineering, National Technical University of Athens, 157 73 Zographou, Athens, Greece;Department of Archive and Library Sciences, Ionian University, Plateia Eleftherias, Palea Anaktora, 49000 Corfu, Greece;Department of Computing, Imperial College, 180 Queen's Gate, London SW7 2BZ, UK

  • Venue:
  • Theoretical Computer Science
  • Year:
  • 2003

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Abstract

Linear Datalog programs are programs whose clauses have at most one intensional atom in their bodies. We explore syntactic classes of Datalog programs (syntactically non-linear) which turn out to express no more than the queries expressed by linear Datalog programs. In particular, we investigate linearisability of (database queries corresponding to) piecewise linear Datalog programs and chain queries: (a) We prove that piecewise linear Datalog programs can always be transformed into linear Datalog programs, by virtue of a procedure which performs the transformation automatically. The procedure relies upon conventional logic program transformation techniques. (b) We identify a new class of linearisable chain queries, referred to as pseudo-regular, and prove their linearisability constructively, by generating, for any given pseudo-regular chain query, the Datalog program corresponding to it.