Generalization as described before is applied to the clauses of a theory, i.e. facts and rules, resulting in more general rules. We have also developed a new technique for abduction. In addition to the Horn-clause theory consisting of facts and rules and a set of integrity constraints IC. we also postulate a set of distinguished ground literals called abducibles and a goal which drives the abduction process.
By abduction we want to find a set of hypotheses such that we can derive the (positive) example from . In the context of theory revision gives the new theory which again must be consistent with IC, the set of integrity constraints:
Consider the following example where we have two rules for the
recyclability of polypropylenes:
The first rule expresses that a polypropylene can be recycled only
in a closed circle, if it contains a flame retardent agent as a fluent additive.
This is because the flame retardent agent produces toxic dioxin on ultimate
For a pure polypropylene there is no restriction a recyclability.
In two facts we also have that hostalen ppk_1060 contains a
flame retardent fluent additive.
polypropylene(X) hostalen (X)
If we declare additive and pure as abducibles and ask the query how ppk_1060 can be recycled
?- recyclable(RecKind,ppk_1060)we get two answers: The first, unconditional answer
RecKind = closed_circlesays that ppk_1060 can be recycled in a closed circle. The second, conditional answer
RecKind = unrestrictedis an abductive solution: under the condition that ppk_1060 is pure, it can be recycled unrestricted.