Page 154 - DCAP310_INTRODUCTION_TO_ARTIFICIAL_INTELLIGENCE_AND_EXPERT_SYSTEMS

Introduction to Artificial Intelligence & Expert Systems

Notes reasoning with facts easy. But using logical formalism complex structures of the world, objects
and their relationships, events, sequences of events etc. cannot be described easily. A good
system for the representation of structured knowledge in a particular domain should posses the
following four properties:
(i) Representational Adequacy: The ability to represent all kinds of knowledge that are
needed in that domain.
(ii) Inferential Adequacy: The ability to manipulate the represented structure and infer new
structures.
(iii) Inferential Efficiency: The ability to incorporate additional information into the knowledge
structure that will aid the inference mechanisms.

(iv) Acquisitional Efficiency: The ability to acquire new information easily, either by direct
insertion or by program control.
The techniques that have been developed in AI systems to accomplish these objectives fall under
two categories:
1. Declarative Methods: In these, knowledge is represented as static collection of facts which
are manipulated by general procedures. Here, the facts need to be stored only one and
they can be used in any number of ways. Facts can be easily added to declarative systems
without changing the general procedures.
2. Procedural Method: In these, knowledge is represented as procedures. Default reasoning
and probabilistic reasoning are examples of procedural methods. In these, heuristic
knowledge of “How to do things efficiently” can be easily represented.
In practice, most of the knowledge representation employ a combination of both. Most of the
knowledge representation structures have been developed to handle programs that handle
natural language input. One of the reasons that knowledge structures are so important is that
they provide a way to represent information about commonly occurring patterns of things such
descriptions are some times called schema. One definition of schema is:
“Schema refers to an active organization of the past reactions, or of past experience, which must always be
supposed to be operating in any well adapted organic response”.
By using schemas, people as well as programs can exploit the fact that the real world is not
random. There are several types of schemas that have proved useful in AI programs. They
include:
(i) Frames: Used to describe a collection of attributes that a given object possesses (e.g.:
description of a chair).
(ii) Scripts: Used to describe common sequence of events (e.g.:- a restaurant scene).
(iii) Stereotypes: Used to described characteristics of people.

(iv) Rule Models: Used to describe common features shared among a set of rules in a production
system.
Frames and scripts are used very extensively in a variety of AI programs. Before selecting any
specific knowledge representation structure, the following issues have to be considered.
(i) The basis properties of objects, if any, which are common to every problem domain must
be identified and handled appropriately.
(ii) The entire knowledge should be represented as a good set of primitives.

148 LOVELY PROFESSIONAL UNIVERSITY