In designing the object model for the unification problem solver, we followed the standard AI practice of distinguishing between the representation of well-formed expressions (classes implementing the...

In designing the object model for the unification problem solver, we followed the standard AI practice of distinguishing between the representation of well-formed expressions (classes implementing the interface unifiable) and the definition of the inference strategy in thenodes of the solution tree (descendents of AbstractSolutionNode). This chapter’s expert system shell built on that distinction. More importantly, because we were not changing the basic inference strategy other than to add certainty estimates, we approached the expert system by defining subclasses to SimpleSentenceSolutionNode and AndSolutionNode, and reusing the existing nextSolution method. If, however, we were changing the search strategy drastically, or for other reasons discussed in 25.4, it might have been more efficient to retain only the representation and rewrite the inference strategy completely. As an experiment to explore this option, rewrite the expert system shell without using AbstractSolutionNode or any of its descendants. This will give you a clean slate for implementing reasoning strategies. Although this does not make use of previously implemented code, it may allow making the solution simpler, easier to use, and more efficient. Implement an alternative solution, and discuss the trade-offs between this approach and that taken in the chapter.