Expert system

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Expert systems are a kind of computer software that is able to solve certain kinds of problems.

In education, expert systems are used in various kinds of artificial intelligence and education projects, e.g. intelligent tutoring systems, intelligent learning environments, adaptive hypertext systems. They are also in use as a kind of simulation.

See also: artificial intelligence (expert systems are one of its subfields)

Definition by an example

Most expert systems are rule based. Let's explain how this works with an example taken from a text by young Pierre Dillenbourg (1994).

Let us imagine that the travel agency trainee has to solve the following problem:

	Problem 22
	Mr Hubert wants to go from Geneva to Igloolik, Canada.
	His is member of the frequent flyer programme of Swissair
	Departure: 1.04.95	Return: 10.05.95

The standard way to do support interactions about this problem would be to store the solution:

	Solution 22
	Flight SR434 Geneva - Zurich 	1.04.94 	9 H 40
	Flight SR121 Zurich - Ottawa 	1.04.94 	11 H 45
	Flight AC101 Ottawa - Frobisher	2.04.94	9 H 30
	Flight AC123 Frobisher-Igloolik	2.04.94	16 H 20

Another approach is to AI techniques to model the reasoning process which led to that solution. Knowledge modelling techniques decompose the reasoning process into numerous intermediate steps or decisions. The knowledge necessary for each step or decision is generally expressed as an 'IF-THEN' rule. Here are a few examples of rules that could be used for solving the problem presented above:

Rule 12
  IF the destination is a remote and unknown place,
  THEN plan the trip via a major city in the area
Rule 33
  IF the local flight is done by a company
  THEN plan the international flight with this company
Rule 122
  IF the customer is part of the frequent flyer programme of a company and if this company has a flight to the customer's destination
  THEN select a flight with this company

Each of these rules encodes a fragment of expertise. The system reasons by checking the 'IF' part of each rule. If the conditions described in the 'IF' part are matched, the system activates the 'THEN' part of the rules. The rules are general: the term 'a company', 'destination' or 'customer' are instantiated by the data of this problem. Some of these rules may be contradictory for some cases, as the 33 and the 122. The system selects the rules and activates them until the problem is solved. In real systems, the rule syntax is of course more formal than the examples above. The systems based on such a set of rules are generally named, knowledge-based, rule-based systems or expert systems. The system component which selects rules, makes the deductions and updates the problem state is called the inference engine.

By decomposing the expertise into fragments, we also decompose the reasoning into intermediate steps. These steps constitute the 'solution path'. The main advantage is that the system can interact about any of these steps: Zurich - Ottawa - Frobisher. For instance, if the learner selects Toronto instead of Ottawa, the system may ask the learner to justify his choice or may present the reasons why it selected Ottawa.

The second advantage of AI techniques is that the system can explain its solution. In general, the explanation is the sequence of rules which have been used by the expert to reach the solution (the 'trace' of its reasoning).

Software and Formats

Expert systems can be built with special purpose software kits, or embedded libraries or (rarely) from scratch. Many systems existed in the late eighties and early nineties. Today there seems to be less variety.

Expert system shells

  • CLIPS A popular tool for building expert systems (Unix, PC, Mac).
    • “CLIPS is a productive development and delivery expert system tool which provides a complete environment for the construction of rule and/or object based expert systems. Created in 1985, CLIPS is now widely used throughout the government, industry, and academia.” ([1])
    • CLIPS is written in C and can be embedded within procedural code, called as a subroutine, and integrated with languages such as C, Java, FORTRAN and ADA. There exist several related systems, e.g. JESS or D3web
    • CLIPS (Wikipedia)
  • JESS is a rule engine for the Java platform derived from CLIPS. The project is well alive and popular. JESS has been interfaced to web applications. Free for academic use.
  • d3web is a Java-based prototyping and development toolkit for distributed knowledge systems. It includes the knowledge modelling environment KnowME, a visual knowledge acquisition, evaluation, and management tool. Claims are made that this system could be used for problem-based learning (last updated 2008).
    • d3web, home page Universität Würzburg
  • The Lisa Project is a platform for the development of Lisp-based Intelligent Software Agents. Lisa is a production-rule system implemented in the Common LISP Object System (CLOS), and is heavily influenced by CLIPS and the Java Expert System Shell (JESS).
  • Earnest AI is a simple PHP-MYSQL expert system, seems to make use of three SQL tables that you will have to populate. (Alpha in June 2010, not tested).
  • Simple Hierarchical Ordered Planner (SHOP, JSHOP,SHOP2, JSHOP2). are domain-independent automated-planning systems. They are based on ordered task decomposition, which is a type of Hierarchical Task Network (HTN) planning.


Most expert systems are implemented with a production system. Generally, these rule-based systems don't use standardized rule and data formats. However, this may change with the ambitious semantic web project(s).


Advancement of Artificial Intelligence, btw. a good resource site with other AI resources)


  • Burton, R.R. & Brown, J.S. (1982) An investigation of computer coaching for informal learning activities. In D. Sleeman & J.S. Brown (Eds), Intelligent Tutoring Systems (pp. 201-225). New York: Academic Press.
  • Clancey, W.J. (1987) Knowledge-based tutoring: the Guidon Program. Cambridge, Massachusetts: MIT Press.
  • Dillenbourg, P. (1994). The role of artificial intelligence techniques in training software, Paper presented at LEARNTEC 1994. PDF.
  • Steels L (1990) Components of Expertise. AI Magazine, vol.11, 2,pp. 28-49.
  • Wenger, E. (1987). Artificial Intelligence and Tutoring Systems, Los Altos: Morgan Kaufmann.