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. 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 (eg: description of a chair).
(ii) Scripts:- Used to describe common sequence of events(eg:- a restaurant
(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.
(iii) Mechanisms must be devised to access relevant parts in a large knowledge