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dfg2dfg - calculate approximations of problems
dfg2dfg [-horn] [-monadic] [-linear] [-shallow] [infile] [outfile]
dfg2dfg is a program that reads clauses from an input file in DFG syntax. It then
calculates an approximation of the clause set depending on the command line options.
Finally it writes the approximated clause set in DFG syntax to a file.
If neither infile nor outfile are given, dfg2dfg reads from standard input and writes to
standard output. If one file name is given, it reads from that file and writes the output
to standard output. If more than one file name is given, dfg2dfg reads from the first
file and writes to the second.
The approximations are described in technical detail in the separate paper dfg2dfg.ps
included in the SPASS distribution.
dfg2dfg has four different command line options that may be combined.
This option enables the transformation of non-horn clauses into horn clauses. Each
non-horn clause with n positive literals is transformed into n horn clauses, where the
i-th clause contains the i-th positive literal and all negative literals of the non-
horn clause. See also section 3 of the paper.
With this option atoms with non-monadic predicate symbols are transformed into monadic
atoms. If n is omitted or n=1 a term encoding is applied, i.e., all non-monadic
predicates are moved to the term level. With n=2 a projection is applied. All non-
monadic atoms are replaced by their monadic argument projections. See section 4.1
section 4.2 of the paper for more details.
This approximation transforms a clause with monadic literals and non-linear variable
occurrences in succedent atoms, into a new clause with possibly more negative
literals, that doesn't contain any non-linear variables in the succedent. See section
5 of the paper for details.
This transformation tries to reduce the depth of the terms in positive literals. The
transformation is applied to horn clauses with monadic literals only. If n is omitted
or n=1 a strict transformation is applied, that is equivalence preserving, however.
For n=2 some preconditions are removed. This allows the transformation to be applied
more often, but the transformation isn't equivalence preserving any more. For n=3
even more preconditions are removed. Take a look at section 6.n of the paper for the
details of the command line option -monadic=n.
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