# Knowledge Representation in Artificial Intelligence

In this article, we are going to study how the stored knowledge in the database of the agent is represented? We will learn about what knowledge representation actually means in the terms of Artificial Intelligence and what types of knowledge representation exist for an agent?
Submitted by Monika Sharma, on June 02, 2019

The term Knowledge representation, as the name suggests is the way the knowledge is represented in the storage system of the agent. We all very well know that any of the computer systems, the data is stored in a database. But there should be a proper layout of this data in the database so that the agent can easily figure out the extracts from the present. In an intelligent agent, knowledge can be represented in two ways:

1. Propositional logic and
2. Predicate logic

Note: At this level, we will discuss only about the first order predicate logic.

### 1) Propositional Logic

In propositional logic, each sentence is classified as a declarative sentence. A declarative sentence is a sentence or proposition which is either True or False. In this type of logic in which our sentence cannot be partially correct. It has to be either completely a yes, or a no.

In the propositional logic, atomic sentences are combined by connectives, and each sentence is represented by a variable. This variable is unique.

Example:

```    A: It is hot
B: It is humid
Therefore, A^B represents 'It is hot and humid'.
```

Following connectives are used to connect the sentences in propositional logic:

```    Not :   ~
And :   ^
Or  :   v
Implies:   ->
If and only if: <->
```

### 2) Predicate logic (First order Predicate Logic)

In the predicate logic system of knowledge representation, it is assumed that the word contains object, relations, and functions. The Predicate logic is a symbolized reasoning in which we can divide the sentence into a well-defined subject and predicate. The subject is defined by the predicate. It should be noted that the predicate can only refer to a single subject.

Example:

```    Ravi likes peanuts
Predicate logic for above statement: like (Ravi,Peanuts)
Here, Ravi is subject, like is a predicate and peanuts is
the value that the predicate defines for the subject.
```