Languages & Environments

Example

In this example we could ask the program to tell us whether Judy drives a fast car by typing the query:

?drives_fast_car(judy)

The result would be YES since the goal is satisfied.

If we asked:

?drives_fast_car(james)

then the result would be NO as drives_car(james, porche) would fail and the goal is not satisfied.

Contrast this with a procedural language where the programmer would need to set up a structure to hold the knowledge and predefine its type (string, number etc). Then they would need to describe the steps taken to search the structure in order to answer the query.

X and Y represent variables; when using Prolog, variables should always be written as capital letters but declarative languages do not require the programmer to declare a data type. It is necessary to be able to read, understand and create simple facts and rules in the format shown.

Queries depend upon in-built algorithms that will carry out pattern matching to return a result. Heuristic, breadth-first and depth-first searches are often used to perform pattern matching when querying a knowledge base.

Declarative languages like Prolog allow for the use of self-modifying code. This means that during execution the program can modify the facts and rules that it holds if necessary.