flex Expert System Toolkit - LPIS

Appendix A - Examples 172
The Identification Algorithm
The previous sections have described a small section of the animal kingdom,
including the inter-relationships of different species (the frame hierarchy) and
some of their characteristics (default values).
The following KSL program can be used to identify a particular species
within the example. Note, though, that the algorithm itself is not specific to
the example, but could equally be used for identifying classes within any
taxonomy.action run(Frame,PosAttribs,NegAttribs)
do [ isa_frame( Frame, _ ) or isa_instance(Frame,_)
]
and for every PosAttr-PosVal is included in
PosAttribs
do check [ the PosAttr of Frame includes PosVal
or the PosAttr of Frame is equal to PosVal
]
end for
and for every NegAttr-NegVal is included in
NegAttribs
do check [ the NegAttr of Frame does not
include
NegVal and the
NegAttr of Frame is not equal to
NegVal
]
end for .
Given a set of positive clues and a set of negative clues, the algorithm will
identify any class which has each of the positive attributes but none of the
negative attributes.
isa_frame/2 and lookup/3 are built-in flex predicates for retrieving the
names of frames and for looking up values of frame attributes, respectively.
The lookup/3 procedure will automatically take into account any
inheritance through the frame hierarchy.
Some Example Questions
Using the identification algorithm above we can ask, for example, the
following two questions :
• Which type of animal eats meat ?
• Which type of animal lives on land, is medium in size but does not eat
meat ?
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