Rule-based system

From HandWiki

In computer science, a rule-based system is used to store and manipulate knowledge to interpret information in a useful way. It is often used in artificial intelligence applications and research. Rule-based systems require a set of facts or source of data, and a set of rules for manipulating that data. These rules are sometimes referred to as ‘If statements’ as they tend to follow the line of ‘IF X happens THEN do Y.[1]

Normally, the term rule-based system is applied to systems involving human-crafted or curated rule sets. Rule-based systems constructed using automatic rule inference, such as rule-based machine learning, are normally excluded from this system type.


A classic example of a rule-based system is the domain-specific expert system that uses rules to make deductions or choices.[2] For example, an expert system might help a doctor choose the correct diagnosis based on a cluster of symptoms, or select tactical moves to play a game.

Rule-based systems can be used to perform lexical analysis to compile or interpret computer programs, or in natural language processing.[3]

Rule-based programming attempts to derive execution instructions from a starting set of data and rules. This is a more indirect method than that employed by an imperative programming language, which lists execution steps sequentially.


A typical rule-based system has four basic components:[4]

  • Match: In this first phase, the left-hand sides of all productions are matched against the contents of working memory. As a result a conflict set is obtained, which consists of instantiations of all satisfied productions. An instantiation of a production is an ordered list of working memory elements that satisfies the left-hand side of the production.
  • Conflict-Resolution: In this second phase, one of the production instantiations in the conflict set is chosen for execution. If no productions are satisfied, the interpreter halts.
  • Act: In this third phase, the actions of the production selected in the conflict-resolution phase are executed. These actions may change the contents of working memory. At the end of this phase, execution returns to the first phase.
  • Temporary working memory.
  • A user interface or other connection to the outside world through which input and output signals are received and sent.

See also


  1. "Rule-Based System" (in en). 
  2. Crina Grosan; Ajith Abraham (29 July 2011). Intelligent Systems: A Modern Approach. Springer Science & Business Media. pp. 149–. ISBN 978-3-642-21004-4. 
  3. Sin-Wai Chan (13 November 2014). Routledge Encyclopedia of Translation Technology. Routledge. pp. 454–. ISBN 978-1-317-60815-8. 
  4. "What is a rule-based system?". 
  5. Cabitza, F., & Dal Seno, B. (2005). "DJess-A Knowledge-Sharing Middleware to Deploy Distributed Inference Systems.". International Journal of Computer and Information Engineering 2: 66–69. doi:10.1109/PERSER.2005.1506416.