Understanding logic programming

This paradigm is based on formal logic. A program written in a language that implements this paradigm is constructed of a set of sentences in a logical form that will express facts and rules about a specific problem domain.

This might sound complicated and strange, but as we will see, the basic concepts of this paradigm are rather simple. Consider the following diagram:

Figure 10.20 – A family tree

In the preceding diagram, we can see a family tree. Looking at it, we can see the following:

• Anna and Bob have a child, Lisa.
• Lisa and Fred have a child, Karen.
• Fred and Sue have a child, John.
• Karen's grandparents are Anna and Bob.

In a programming language that uses logic programming, we can define this family tree using something called predicates. This will look something like this:

mother(anna,lisa).
mother(lisa,karen).
mother(sue,john).
father(bob,lisa).
father(fred,karen).
father...