Prolog
Introduction
Prolog is a programming language which is specifically designed for Artificial Intelligence that implements a subset of logic programming. Prolog is generally used for natural language processing, theorem-proving and knowledge representation. Prolog has its origin in the early 1970s, when it was developed at the programming language department of the University of Marseille.
History of Prolog
The idea of logic programming was first proposed by the French logician Alain Colmerauer in the early 1970s. He proposed a variant of the original Prolog language, based on the resolution principle, called Prolog II. The first implementation of Prolog was developed by Robert Kowalski in 1972 at the University of Edinburgh. The first Prolog system for commercial use was released in 1977 as part of the DEC-10 operating system. In the following years, Prolog systems were developed for a variety of platforms, such as the IBM PC in 1984, the Sun computer in 1985, and Macintosh computers in 1988. In 1993, the International Organization for Standardization (ISO) standardized the Prolog language, creating an ISO Prolog standard. This version was based on the Edinburgh Prolog system and the DEC 10 Prolog system. The ISO Prolog standard was later revised and updated in 1995 and 2002. Since then, Prolog has been used in a wide range of applications, such as natural language processing, expert systems, and robotics. Prolog code can be used to create intelligent agents, which are able to interact with their environment and react to events and changes. The first implementation of Prolog was developed by Alain Colmerauer and Robert Kowalski at the University of Marseille in 1971 as a logic-based language. At the time, they saw it as a way to represent and solve natural language problems. Their work was based on the formal logic system known as Resolution Principle. In the 1980s, Prolog began to gain momentum as a general-purpose programming language. By the 1990s, Prolog had become one of the most widely used AI languages in research and education.
Features of Prolog
Prolog uses the declarative programming paradigm, which means that you define what you want the program to do but not how to do it. Programs written in Prolog are composed of logical statements, rules and facts. The programmer expresses a query on the data and Prolog will then search for a solution to the query using the logical statements, rules, and facts. Prolog is rule-based, allowing you to create rules that apply to certain data. These rules can be used to search for solutions, without having to explicitly specify the steps required to find the solution. Prolog is also highly efficient at searching through large sets of data to find a solution. For example, Prolog can be used to search through a large database and find all records that contain a certain value. Prolog is capable of creating solutions to problems that would otherwise require a large amount of code to implement. This makes Prolog ideal for creating AI systems, which require the ability to find solutions to complex problems quickly and efficiently.
The following are key features of Prolog:
- Logical syntax: Prolog programs are written in a logical syntax that allows users to define facts and rules about the data being processed. This allows users to easily “ask” questions about their data.
- Declarative: Prolog is a declarative language, meaning it declares facts and rules rather than providing instructions on how to implement those facts and rules. This allows Prolog programs to be concise and efficient.
- Backtracking: Prolog uses built-in backtracking to find solutions to problems. It tests each solution one at a time and if a better solution is found, it discards the previous one.
- Easy to learn: Prolog is relatively easy to learn compared to other programming languages, making it accessible to a wide range of users.
Origins
Prolog was first developed by Alain Colmerauer and Philippe Roussel at the University of Marseille, France in 1972 as a project for the National Institute for Research in Computer Science and Automation (INRIA). The initial version of Prolog was implemented in Prolog I and later in Prolog II. The language was designed to be based on formal logic, making it useful for tasks such as theorem proving and artificial intelligence. Prolog was initially written in ALGOL-W, but was soon recoded in the B-Prolog dialect. The language was designed by Colmerauer, who also wrote the influential book Logic Programming: Foundations of Logic Programming, which established the principles of Prolog and helped spread its use.
Features
Prolog is an imperative scripting language that consists of a set of logical operations compiled into a single expression. Prolog programs are composed of facts and rules, written in a manner similar to the predicate calculus. Facts are statements about the data, while rules can be used to define the behavior of the program. The language features built-in predicates, which allow for versatile operations such as loops and recursion. Predicates are functions that take input, operate on it, and then return an answer. Prolog’s syntax also allows for powerful pattern recognition techniques, making it useful for tasks such as database querying and natural language processing.
Popularity
Since its initial release, Prolog has been widely adopted in the fields of artificial intelligence and database management. Prolog is the de facto language for researchers in AI and has been used for natural language processing, expert systems, robotics, and computer vision. It has been used to create a number of successful applications including Prolog embedded systems, natural language understanding systems, and robotic navigation systems. Prolog has also been used extensively in the development of software engineering tools, such as the Mozilla Firefox web browser, the WordNet knowledge database, and the Prolog IDE.
Advantages of Prolog
One of the primary benefits of Prolog is its declarative syntax, which makes it easier to read and write code. This advantage allows developers to write applications quickly and easily. In addition, Prolog is a powerful tool for artificial intelligence and natural language processing. Prolog also supports a wide range of features, such as data structures, pattern matching, unification, pattern matching, arithmetic and logical operations, backtracking, meta-programming, and multi-threading. These features make it easy for developers to create complex applications with Prolog. Another benefit of Prolog is that it is highly portable, meaning it can be used on a variety of platforms and operating systems. It is also open source, so developers can make changes to the code to suit their needs.
Using Prolog
Prolog is a powerful language that is used to solve complex problems. It can be used to create intelligent agents, solve puzzles, generate music, and more. Prolog programs are composed of facts, rules, and queries. Facts are simply pieces of information that are known to be true. Rules are statements that describe how facts can be inferred or combined to form new facts. Queries are statements that ask questions about the data.
Here is an example of some Prolog code:
/* Facts */
likes(john,mary).
likes(mary,john).
/* Rules */
friend(X,Y) :- likes(X,Y), likes(Y,X).
/* Query */
?- friend(john,mary).
In this example, we have two facts, likes(john, mary) and likes(mary, john), and one
rule, friend(X,Y) :- likes(X,Y), likes(Y,X). The query ?- friend(john, mary) will return true because
both likes(john, mary) and likes(mary, john) are true.
This is a simple program that illustrates the basic structure of Prolog.
% This is a Prolog program
if likes(john,mary).
likes(john,mary).
else.
not_likes(john,mary).
end_if.
This Prolog program states that if John likes Mary, then it will return true; otherwise, it will return false.
This is another example that illustrates a complex pattern matching operation.
% This is a Prolog program
match([H|T],L) :-
match0(H,L),
match(T,L).
match([],_L).
match0(H,L):-
select(H,L,R).
This program is a recursive function that will search for a pattern in a list. The function will check the first element of the list and search for a match in the remaining elements, and then repeat the process until the end of the list. If a match is found, the function will return true; otherwise, it will return false.
Here is an example of a Prolog program that prints out “hello world”:
main :-
write('Hello World!'), nl.
This program prints out the string “Hello World!” to the screen. The write/1 predicate is used to write text to the
screen. The nl/0 predicate is used to move to the next line after printing the text.
Here is an example of a Prolog program that calculates the factorial of a number:
factorial(0, 1).
factorial(N, F) :-
N > 0,
N1 is N - 1,
factorial(N1, F1),
F is N * F1.
This program uses a recursive approach to calculate the factorial of a number. First, it checks if the number is 0. If it is, then the result is 1. Otherwise, it calls itself with the number minus one, and then multiplies the result by the original number.
Finally, here is an example of a Prolog program that calculates the Fibonacci sequence:
fib(0, 0).
fib(1, 1).
fib(N, F) :-
N > 1,
N1 is N - 1,
N2 is N - 2,
fib(N1, F1),
fib(N2, F2),
F is F1 + F2.
This program uses a recursive approach to calculate the nth number in the Fibonacci sequence. First, it checks if the number is 0 or 1. If it is, then the result is 0 or 1 respectively. Otherwise, it calls itself twice with the number minus one and two, and then adds the two results together.
To give you an idea of how Prolog works, here is an example of a Prolog program that evaluates whether a number is prime:
prime(2).
prime(3).
prime(X) :- X > 3,
Y is X - 1,
prime(Y),
not(divisible(X,Y)).
divisible(X,Y) :- 0 is X mod Y.
This code defines three predicates: prime/1, divisible/2, and not/1. The prime/1 predicate is used to test whether a given number is prime. It uses the other two predicates to do so, calling the divisible/2 predicate to test whether the number is divisible by any numbers less than itself and using the not/1 predicate to negate the result.
Conclusion
Prolog is a powerful and versatile programming language originally designed for AI applications. It has since gained widespread use across many disciplines, ranging from natural language processing to game playing. Its logical syntax and built-in backtracking make it both concise and powerful, allowing users to rapidly develop applications that utilize rich data sets.