How to use it. Choose a system in the title bar. Ask me runs a consultation: the inference engine works backwards from each possible conclusion and asks you only the questions it needs (press Why? at any question). From facts lets you tick what you know and watches forward chaining fire the rules. Edit rules lets you change the facts and rules, or add your own; the other modes then use your version. The strip at the top shows the parts of an expert system, lit up as each one works: click one to read about it.
The parts
- Knowledge base: the facts about the subject, gathered from human experts.
- Rule base: the rules, written
IF … THEN …, that link the facts. (Some books count it as part of the knowledge base.)
- Inference engine: the reasoning part. It applies the rules to the facts the user gives, to reach conclusions, and decides what to ask next.
- User interface: asks the questions (often Yes/No) and shows the conclusions and advice.
- Explanation system: says how a conclusion was reached ("because you said …") and why a question is being asked.
A knowledge base editor lets the experts (or a knowledge engineer) add and change facts and rules: that is what Edit rules is.
Chaining
Backward chaining is goal-driven: it picks a possible conclusion and works back through the rules to the facts it needs, asking about them. It suits diagnosis. Forward chaining is data-driven: it starts with the facts it is given and fires every rule whose IF part is true, adding each conclusion as a new fact, in cycles, until nothing new can be concluded. Either way, one rule's conclusion can be another rule's condition: that is the chain.
Uses and limitations
Uses: medical diagnosis, car and machine fault-finding, plant and animal identification, mineral prospecting, financial and insurance decisions, legal advice, chess. Advantages: consistent answers, available at any time and in many places at once, quick, can explain its reasoning, and keeps the knowledge of experts who retire. Limitations: no common sense, judgement or empathy; only as good as its rules (and wrong outside them); expensive to build and to keep up to date; and people may trust it too much. It can't learn on its own.
Common exam mistakes: mixing up the knowledge base (facts) and the inference engine (reasoning); describing forward chaining as starting from the goal; and listing "it can think for itself" as an advantage.
Objective: Cambridge International AS & A Level Information Technology (9626), expert systems: their components, how they are created and used, forward and backward chaining, and their uses and limitations. The two systems here are teaching examples, not real advice.
Where this fits
- Cambridge: Cambridge IGCSE Information and Communication Technology (0417); Cambridge IGCSE Computer Science (0478); Cambridge A Level Information Technology (9626); Cambridge AS Level Information Technology (9626) Goes beyond Cambridge IGCSE Information and Communication Technology (0417): Forward and backward chaining go beyond 0417.
Goes beyond Cambridge IGCSE Computer Science (0478): Forward and backward chaining go beyond 0478.
- Pearson Edexcel International: Edexcel International A Level Information Technology
