- Predicates are separated into three categories: abducibles, defeasible and background (non-defeasible).
- Literals are represented using prolog terms. A negative literal is a term of the form neg(L).
- The language for representing various theories (problem domains) is
given by rules of the form:
rule(Signature, Head, Body).
where,
-
Head is a literal
-
Body is a list of literals
-
Signature is a compound term composed of a rule name together with selected variables
from the Head and Body of the rule.
- The special predicate
prefer/2 is used
to encode locally the relative strength of rules in the theory,i.e.
rule(Signature, prefer(Sig1,Sig2), Body).
means that the rule with signature Sig1 has higher priority
than the rule with signature Sig2 provided that the
preconditions in the Body hold.
- Abducible literals are specified using the special predicate abducible/2,
abducible(Literal, Preconditions).
- The statement
conflict(Sig1,Sig2) indicates that the rules
with signatures Sig1 and Sig2 are conflicting.
In many cases conflict(Sig1,Sig2) will be true iff the heads of
the rules Sig1 and Sig2 are contrary literals,
but other rules can also be declared as conflicting by the designer
of the domain description.
