Network Representations
Networks are often used in
artificial intelligence as
schemes for representation.
One of the advantages of using a
network representation is that theorists in computer science have
studied such structures in detail and there are a number of
efficient and robust algorithms that may be used to manipulate the
representations.
Trees and Graphs
A tree is a collection of nodes in which each node may be expanded
into one or more unique subnodes until termination occurs. There
may be no termination and an infinite tree results. A graph is
simply a tree in which non-unique nodes are generated; in other
words, a tree is a graph with no loops. The representation of the nodes
and links is arbitrary. In a computer chess player, for example, nodes might
represent individual board positions and the links from each node the
legal moves from that position. This is a specific instance of
a problem space. In general,
problem spaces are graphs in which the nodes represent states and
the connections between states represented by an operator that
makes the state transformation.
IS-A Links and Semantic Networks
In constructing concept hierarchies, often the most important means
of showing inclusion in a set is to use what is called an IS-A link,
in which X is a member in some more general set Y. For example, a DOG
ISA MAMMAL. As one travels up the link, the more general concept is
defined. This is generally the simplest type of link between concepts
in concept or semantic hierarchies.
The combination of instances and classes connected by ISA links in
a graph or tree is generally known as a semantic network. Semantic
networks are useful, in part, because they provide a natural structure
for inheritance. For instance, if a DOG ISA MAMMAL then those properties
that are true for MAMMALs and DOGs need not be specified for the DOG;
instead they may be derived via an inheritance procedure. This greatly
reduces the amount of information that must be stored explicitly although
there is an increase in the time required to access knowledge through
the inheritance mechanism. Frames are
a special type of semantic network representation.
Press
UP to go to the property list.
Press
HOME to go to the Table of Contents.