Please start this week's work by reading Winston, Artificial Intelligence, Chapter 6.
Learn the algorithm on p 168, because you'll need it for production systems. Work through the Bagger example. Although it looks frivolous, it illustrates how control passes from one rule to another in production systems, and why there is more than one way to do conflict resolution. As you'll see later, the choice of control and conflict resolution methods defines part of the functional architecture of mind when production systems are used to model cognition.
When you dry-run Bagger, you check the conditions of the rules
against what Winston calls the database. This database
corresponds to short-term memory in the cognitive models. Notice
how the current step is stored in the database (e.g., on the
bottom of p 169,
Step: Check-order), and how it is tested in
rule conditions. This amounts to representing one's goals in
STM, and using them to drive future processing.
This shows how a Bagger-like expert system can be employed for an industrial planning task. XCON frequently appears in the literature because it was one of the most successful commercial expert systems: it performed a task that couldn't be done manually or with a conventional computer program. (An alternative approach would have been for DEC to simplify their product range: but perhaps that's not as much fun as building expert systems).
Work through both the forward- and backward-chaining animal identifiers.
Do you think forward- or backward-chaining is better for synthesis tasks like Bagger? Why?
Winston does not question whether the explanations thus generated are suitable for the user of an expert system (or which type of user, if any, they'd suit). He was writing when it was taken for granted that these rule-by-rule traces would be.
Like XCON, MYCIN is often cited. It was the first backward-chaining expert system, and still serves as the model for many commercial products. It's probably true to say that until 1986 or so, most commercial systems were essentially MYCIN with its medical knowledge replaced by rules on tax-accountancy, telephone fault-diagnosis, or whatever.
Note the difference between STM and LTM.
Don't bother to learn what an ``elementary production system'' is from here --- it's better to take an account from one of the cognitive modellers. The point is that the computer simulation is being restricted to what's believed to be true of the mind's functional architecture. Different workers have different hypotheses about this architecture, and do not come up with exactly the same kind of model.