In Prolog, facts are the simplest form of knowledge representation. They are used to state things that are unconditionally true about the world. This section will cover the basics of defining facts in Prolog, including syntax, examples, and practical exercises.

1. Facts: Statements that are always true.
2. Atoms: Basic constants that represent objects or values.
3. Predicates: Functions that express relationships between atoms.

A fact in Prolog is written as a predicate followed by a period (.). The general form is:

Consider the following facts about family relationships:

In these examples:

• parent is the predicate.
• john, mary, susan, and tom are atoms representing individuals.

Let's define some facts about pets:

Here, pet is the predicate, and dog, cat, and fish are atoms.

We can also define facts with more than one argument to represent relationships:

In this case, owns is the predicate, and the pairs (john, dog), (mary, cat), and (susan, fish) represent the relationships.

Define facts to represent the following information:

1. Alice owns a rabbit.
2. Bob owns a parrot.
3. Carol owns a hamster.

Solution:

Define facts to represent the following relationships:

1. John is the father of Mary.
2. Mary is the mother of Susan.
3. Susan is the sister of Tom.

Solution:

1. Forgetting the Period: Each fact must end with a period (.). Omitting the period will result in a syntax error.
2. Case Sensitivity: Prolog is case-sensitive. Predicates and atoms should start with a lowercase letter.
3. Consistency: Ensure that the predicates and arguments are used consistently throughout your facts.

In this section, we learned how to define facts in Prolog. Facts are the building blocks of Prolog programs and are used to represent unconditionally true statements about the world. We covered the syntax of facts, provided practical examples, and included exercises to reinforce the concepts. Understanding how to define facts is crucial for progressing to more complex Prolog programming topics.

Next, we will explore how to define rules in Prolog, which allow us to express more complex relationships and logic.