Changing the Prolog Database

Abstract

This chapter describes the built-in predicates for adding clauses to or deleting clauses from the Prolog database and shows how to use them to create and maintain a database of related facts within the overall Prolog database.

After reading this chapter you should be able to:

• Define a predicate which causes one or more clauses to be added to or deleted from the Prolog database

• Define predicates to create and manipulate a database of related facts within the Prolog database

Practical Exercise 8

• (1) Define and test a predicate add_data which reads a series of names of animals (e.g. cat, dog, mouse) entered by the user, terminated by end. It should add a corresponding series of facts, e.g. animal(dog) to the Prolog database, ignoring any names that have already been entered.

• (2) Define and test a predicate display_animals which lists the names of all the animals in the database, one per line.

• (3) Define and test a predicate remove2 which removes any clauses corresponding to either a dog or a cat from the database, if they are present, and otherwise has no effect.