flex Expert System Toolkit - LPIS

6. Anatomy of a flex Program 55
6. The Anatomy of a flex Program
This chapter describes the basic composition of a flex program using the
Knowledge Specification Language (KSL). The KSL’s structures and syntax
are described in more detail in the next chapter.
A flex program comprises a series of sentences written in the KSL
(Knowledge Specification Language). Each sentence starts with a KSL
keyword and ends with a full stop. These sentences are compiled into Prolog
clauses by the flex compiler. (See the Runtime Interpretation of KSL
chapter).
A KSL sentence begins with one of the following keywords:
action
constraint
data
demon
do
frame
function
group
instance
launch
question
relation
rule
ruleset
synonym
template
watchdog
These are all described in detail in the next chapter.
Note that a KSL program does not have to use forward chaining, and may
consist entirely of relations and actions, which are the equivalent of
backward chaining Prolog programs. For example, the following Prolog
program.
sibling( X, Y ):-
parent( Z, X ),
parent( Z, Y ).
may be written using the KSL as follows.
relation sibling( X, Y )
if parent( Z, X )
and parent( Z, Y ).
Either of these may be called from the Prolog command line, e.g.
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