View source for Rule-based system

In [[Computer science|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|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.<ref>{{Cite web |title=Rule-Based System |url=https://www.engati.com/glossary/rule-based-system |access-date=2022-08-17 |website=Engati |language=en}}</ref>

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|rule-based machine learning]], are normally excluded from this system type.

==Applications==

A classic example of a rule-based system is the domain-specific [[Expert system|expert system]] that uses rules to make deductions or choices.<ref name="GrosanAbraham2011">{{cite book|author1=Crina Grosan|author2=Ajith Abraham|title=Intelligent Systems: A Modern Approach|url=https://books.google.com/books?id=c1fzgQj5lhkC&pg=PA149|date=29 July 2011|publisher=Springer Science & Business Media|isbn=978-3-642-21004-4|pages=149–}}</ref>  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|lexical analysis]] to [[Compiler|compile]] or interpret computer programs, or in [[Natural language processing|natural language processing]].<ref name="Chan2014">{{cite book|author=Sin-Wai Chan|title=Routledge Encyclopedia of Translation Technology|url=https://books.google.com/books?id=S0FWBQAAQBAJ&pg=PA454|date=13 November 2014|publisher=Routledge|isbn=978-1-317-60815-8|pages=454–}}</ref>

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.

==Construction==

A typical rule-based system has four basic components:<ref>{{cite web|url=http://www.j-paine.org/students/lectures/lect3/node5.html|title=What is a rule-based system?|work=j-paine.org}}</ref>

* A list of rules or '''rule base''', which is a specific type of [[Knowledge base|knowledge base]].
* An [[Philosophy:Inference engine|inference engine]] or [[Semantic reasoner|semantic reasoner]], which infers information or takes action based on the interaction of input and the rule base. The interpreter executes a [[Production system (computer science)|production system]] program by performing the following match-resolve-act cycle:<ref>{{cite journal
| author= Cabitza, F., & Dal Seno, B.
| title= DJess-A Knowledge-Sharing Middleware to Deploy Distributed Inference Systems. 
| journal= International Journal of Computer and Information Engineering
| year=2005
| volume=2
| pages=66–69
| doi= 10.1109/PERSER.2005.1506416}}</ref>
:* 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|working memory]].
* A [[User interface|user interface]] or other connection to the outside world through which input and output signals are received and sent.

==See also==
* Rule-based programming
* Expert systems
* [[Rewriting]]
* [[Organization:RuleML|RuleML]]
* [[Software:TK Solver|TK Solver]]
* List of rule-based languages
* [[Learning classifier system]]
* [[Rule-based machine learning]]
* [[Biology:Rule-based modeling|Rule-based modeling]]

== References ==
{{Reflist}}

{{Programming language}}
{{Semantic Web}}

[[Category:Artificial intelligence]]

{{Sourceattribution|Rule-based system|1}}