flex Expert System Toolkit - LPIS

1. Introduction 10
Forward Chaining
Forward chaining production rules in flex follow the classical if-then rule
format. Forward chaining is data-driven and is very suitable for problems
which involve too many possible outcomes to check by backward chaining,
or where the final outcome is not known.
The forward chaining inference engine cycles through the current rule
agenda looking for rules whose if conditions can be satisfied, and selects a
rule to use or fire by executing its then part. This typically side affects data
values, which means that a different set of rules now have their conditions
satisfiable.
Flex extends the classical production rule with an optional explanation
facility and dynamic scoring mechanism for resolving conflicts during rule
selection. Rules can have multiple conclusions or actions (either positive or
negative) in their then part .
The rule selection and agenda update algorithms of the forward chaining
engine are flexible, with many built-in algorithms and the option of applying
user-defined algorithms.
Backward Chaining
Search
Backward chaining rules, which correspond closely to Prolog predicates, are
called relations in flex. They have a single conclusion that is true, if all the
conditions can be proven. Backward chaining is often referred to as goaldriven,
and is closely linked to the notion of provability.
Search is one of the key characteristics of expert systems. There are
normally many ways of combining or chaining rules together with data to
infer new conclusions. How to examine only the relevant part of this search
space is a serious consideration with regard to efficiency. The ordering of
rules, the provision of meta-rules (rules about which rules to use) and
conflict-resolution schemes are all ways of helping us produce a sensible
search tree which we can investigate. Prolog-based systems tend to use a
depth-first strategy, whereby a certain path is fully explored by checking
related paths, combined with backtracking to go back and explore other
possibilities when a dead-end is reached.
Frames and Inheritance
Frame hierarchies are similar to object-oriented hierarchies. They allow data
to be stored in an abstract manner within a nested hierarchy with common
properties automatically inherited through the hierarchy. This avoids the
unnecessary duplication of information, simplifies code and provides a more
readable and maintainable system.
flex toolkit