Artificial Intelligence and Soft Computing: Behavioral ... - Arteimi.info

Consequently, we represent the above clause by a semantic net (vide fig 8.4).
The semantic net shown in fig 8.4 describes a mapping from
relationships Instance-of (X, child) and Instance-of (sweet, Y) to relationships
Likes (X, Y). To represent the given clause by an alternative form of semantic
nets, we, for example, first express it in CNF. The CNF of ∀X ∃Y (Instanceof
(X, child) ∧ Instance-of (Y, sweet) Likes (X, Y)) is ∀X ∃Y ( ¬Instanceof
(X, child) ∨ ¬Instance-of (Y, sweet) ∨ likes(X, Y)).
Disjunction
¬ Instances-of
X
Likes
Child Sweet
Fig . 8.5: A representation of ¬ Instance -of ( X, Child ) V
¬ Instance- of ( Y, Sweet ) V Likes ( X , Y ).
Semantic nets can be partitioned into modules, where one or more
modules are subsets of the others. Such modular structure helps reasoning in a
hierarchical fashion and thus is more time efficient. For instance, consider the
semantic net of fig. 8.6, where node ‘g’ corresponds to the assertion given in
the above problem, whereas GS is a general statement. In other words, g is a
special instance of GS. The form of node g, and ∀X, are also shown clearly in
fig. 8.6. It is to be further noted that the entire semantic net is now partitioned
into two modules, one called SI, while the entire space is called SA. The
spaces in a partitioned semantic net [3] are associated with each other by a
subsethood hierarchical relation. For instance, space SI in fig. 8.6 is included
in space SA. The search in a partitioned semantic net thus can be done from
inner to outer space; searching variables or arcs in an opposite direction (i.e.,
from outer to inner space) is not allowed [9].
Y
¬ Instances-of