what is logic programming? explain facts, rules and queries with examplesSee answer
what is logic programming explain facts rules and queries with examples
Question
Basic Answer
Step 1: Defining Logic Programming
Logic programming is a programming paradigm based on formal logic. Instead of specifying how to solve a problem (like in imperative programming), you declare what the problem is, using facts, rules, and queries. The system then uses inference to deduce the answers. Prolog is the most well-known logic programming language.
Step 2: Facts
Facts are statements that are known to be true. They are represented as predicates with arguments.
Example:
parent(john, mary). This fact states that John is a parent of Mary.
Step 3: Rules
Rules define relationships between facts. They have a head (conclusion) and a body (conditions). The head is true if all conditions in the body are true.
Example:
ancestor(X, Y) :- parent(X, Y). This rule states that X is an ancestor of Y if X is a parent of Y.
ancestor(X, Y) :- parent(X, Z), ancestor(Z, Y). This rule states that X is an ancestor of Y if X is a parent of Z, and Z is an ancestor of Y (recursive definition).
Step 4: Queries
Queries are questions posed to the system. The system uses the facts and rules to determine if the query is true and, if so, provides the values that satisfy the query.
Example:
?- ancestor(john, mary). This query asks if John is an ancestor of Mary. Given the facts and rules above, the system would answer ‘yes’.
?- ancestor(X, mary). This query asks who is an ancestor of Mary. The system would return X = john (and potentially others depending on more facts).
Step 5: Putting it Together (Example)
Let’s say we have these facts:
parent(john, mary).parent(john, peter).parent(mary, sue).
And this rule:
sibling(X, Y) :- parent(Z, X), parent(Z, Y), X \= Y. (X and Y are siblings if they have the same parent Z, and X is not Y)
Then the query:
?- sibling(peter, sue).
would return ‘no’ because Peter and Sue don’t have the same parent. However,
?- sibling(X, Y).
might return multiple solutions showing pairs of siblings based on the facts provided.
Final Answer
Logic programming uses facts (true statements), rules (conditional statements), and queries (questions) to deduce answers based on logical inference. The system uses these elements to determine the truth of queries and provide solutions.