dwfs: A program transformation tool for
computing the D-WFS semantics

dwfs is a system for computing the D-WFS semantics of disjunctive logic programs. This system has been developed as a part of the research project DisLoP funded by DFG.

The D-WFS semantics has first been introduced by Brass and Dix. For a description, see

• S. Brass, J. Dix:
  A General Framework for Semantics of disjunctive Logic Programs based on Partial Evaluation.
  Journal of Logic Programming, to appear 1997.
  Extended Abstract appeared at Proc. 12th Int. Conf. on Logic Programming, MIT, 199-213, 1995
  Get a Preliminary Version.

• S. Brass, J. Dix: Characterizations of the Disjunctive Stable Semantics by Partial Evaluation.
  Journal of Logic Programming, to appear 1997. Get a Preliminary Version .

• S. Brass, J. Dix: Characterizing D-WFS: Confluence and Iterated GCWA.
  Logics in Artificial Intelligence (JELIA '96), J.J.~Alferes, L.M. Pereira and E. Orlowska (eds.), Springer LNAI 1126, 268--283, 1996.
  Extended version will appear in the Journal of Automated Reasoning in 1997.
  Get the Journal-Version.

• S. Brass, J. Dix: A General Approach to Bottom-Up Computation of Disjunctive Semantics.
  In: J. Dix, L. Pereira, T. Przymusinski (eds.): Non-Monotonic Extensions of Logic Programming.
  Pages 127-155, LNAI 927, Springer, Berlin.
  Get the Paper.

The dwfs program computes, from an input program in clausal form, the residual program or program remainder, from which the D-WFS semantics can be read off directly. Program remainders, which can only be computed for non--disjunctive programs, are introduced in:

S. Brass, B. Freitag, U. Zukowski: Transformation Based Bottom-Up Computation of the Well-Founded Model. In: J. Dix, L. Pereira, T. Przymusinski (eds.): Nonmonotonic Extensions of Logic Programming Pages 171-201, LNAI 1216, Springer, Berlin.

They are equivalent to residual programs, but are polynomial in size relatively to the size of the original input program, whereas residual programs can grow to be exponential in size.

There are three different computations that dwfs can perform:

• For range-restricted disjunctive Datalog programs, dwfs can compute the residual program using a least-fixpoint approach.
• For disjunctive logic programs, dwfs can compute the residual program by application of all program transformations in turn.
• For non-disjunctive logic programs, dwfs can compute the program remainder.

The prototype implementation and some test cases are available as a gzipped tar file. For a description of parameters, flags and input format, see the user's guide .

If you have questions or comments, please send an email to Jürgen Dix or Katrin Erk.

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