Knowledge Representation
The main methods of knowledge representation (Efraim Turban 1999) are as follows:
 Logic.
 Semantic Network.
 Frames.
 Production Rules.
 Data Structure.
 Algorithm.
 Data Flow Diagram (DFD).
 Unified Modeling Language (UML).
Knowledge Representation Using Logic
One of the oldest methods of knowledge representation is logic. It is a sub division of Philosophy. Many people have defined logic but the most common definitions are as follows:

A reasoning process based on science used to differentiate between correct and incorrect reasoning.

A process used to reason the problem to reach a conclusion or solution.

Method used to distinguish correct knowledge from incorrect knowledge.
Logic is further divided into two types:
 Propositional Logic Calculus.
 Predicate Logic Calculus.
Propositional Logic Calculus
Proposition means a statement is either true or false. Logic is process used to reach the conclusion. Calculus is a term used for computing. Propositional Logic used symbols for computing, such as letters of alphabets. For example, Logic gates are used for Boolean algebra:
 NOT Gate.
 AND Gate.
 OR Gate.
Predicate Logic Calculus
Predicate Logic Calculus is used for AI programming. It is used to represent the knowledge in a delicate way or in a finer way. Predicate Logic concepts and rules are same as used by Propositional Logic. Predicate Programming is like the function prototype programming in C and C++ languages. Predicate is a portion of sentence containing its subjects. Declarative Programming Languages used Predicate Logic Calculus instead of Propositional Logic Calculus, such as PROLOG and LISP. A declarative program is a combination of facts and rules. Rules are relationships of facts.
Knowledge Representation Using Semantic Network
Semantic network is an easiest representation of knowledge. It is a kind of network used to represent the knowledge in graphical format. Semantic network used symbols or nodes to draw. Each node is like an arc. One of the techniques used for analysis to conceptualize the problem and verify the requirements. More close to the way human being stores the knowledge.