As mentioned before, generalization of Horn clauses can be done in different ways, e.g. by generalizing some terms (argument positions) or by dropping entire literals (removing conditions).
Thus, the decision about which generalization operation should be applied is still a problem. Abduction can provide considerable help for making this decision. Consider again the recyclability example introduced in the last paragraph.
If we recognize the fact that hostalen ppk_1060 can be recycled unrestricted (no matter of its pureness) then we have to revise our theory to now cover this (positive) example. By processing the query
?- recyclable(unrestricted,ppk_1060)we obtain the abductive solution
yeswhich gives rise to generalize the recyclable rule for ppk_1060 by dropping this pureness condition. Thus, we substitute the original rule
recyclable(unrestricted,Plastic_Id)by the following generalized one:
Although this is only one example of how abduction and generalization can cooperate in the theory revision framework, it already shows the combined potential for our application.