Manipulating Client Predicates

Dr. Richard S. Wallace
ALICE A.I. Foundation
July, 2005

AIML client Predicates are like variables that are specific to a given
client, such as his or her name, age, gender, occupation, preferences
and so on.  These need not be fixed, and indeed predicates are also
used for such fast changing entities as the values of adverbs such as
he, she and it.  An important special predicate in AIML is the topic,
which can be set in the template, but also used to control the flow of
pattern matching with the AIML <topic> tag.  Another important
built-in predicate is <that/>, which may not be set by the botmaster.

Many AIML systems use different techniques to set predicate default values.
Some use a special externial file, often in XML format, to specify default
predicate values.  Predicate defaults may also be set in AIML itself.  The
purpose of the category with the pattern SET PREDICATES OM is to set all
the default predicate values.  For example, the default predicate value for
"he" is "he" (the predicate itself) and for "has" is "mother" (because everyone
has a mother).  There is also a special meta predicate set to "set".  Recall
that the AAA set assumes a global default predicate return value of OM.
If the meta predicate has not been set, then the SET PREDICATES category
will activate SET PREDICATES OM and set all the default values, including the
meta predicate.  This ensures that SET PREDICATES OM will be activated only
once, because the next time SET PREDICATES is activated, the meta predicate
will no longer be OM, and the recusion will activate the category with the
pattern SET PREDICATES *.