Global variables and DataBase Functions

• Common practise in procedural programming to use global variables - i.e. variables accessible from the entire program
• In Prolog usually use local variables - which are restricted to the clause being used
• Therefore the need to be able to modify program (by adding variables or clauses to it)
• This is very similar to functions performed in a database
• Operations performed usually involve changing the data already present within the database - hence the need to modify the existing information
• A program in Prolog can be viewed as a database made of facts (knowledge) and operations (relations) on this knowledge
• There are predicates in Prolog which help us achieve exactly this - i.e. a program being added to or deleted from by the use of special queries

Achieved by the use of retract and assert and their variations.

 
• assert
• retract