Jess (programming language)

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Developer(s)Sandia National Laboratories
Stable release
7.1p2 / November 5, 2008; 15 years ago (2008-11-05)
LicenseClosed source / Public Domain

Jess is a rule engine for the Java platform that was developed by Ernest Friedman-Hill of Sandia National Labs.[1] It is a superset of the CLIPS programming language.[1] It was first written in late 1995.[1] The language provides rule-based programming for the automation of an expert system, and is frequently termed as an expert system shell.[1] In recent years, intelligent agent systems have also developed, which depend on a similar capability.

Rather than a procedural paradigm, where a single program has a loop that is activated only one time, the declarative paradigm used by Jess continuously applies a collection of rules to a collection of facts by a process called pattern matching. Rules can modify the collection of facts, or they can execute any Java code. It uses the Rete algorithm[1] to execute rules.


While CLIPS is licensed as open source, Jess is not open source. JESS is free for educational and government use but a license is required to use JESS for commercial systems.

Code examples[edit]

Code examples:

; is a comment

(bind ?x 100)

; x = 100

(deffunction max (?a ?b)
             (if (> ?a ?b) then ?a else ?b))

(deffacts myroom
          (furniture chair)
          (furniture table)
          (furniture bed)

(deftemplate car
             (slot color)
             (slot mileage)
             (slot value)

(assert (car (color red) (mileage 10000) (value 400)))

Sample code:

(deftemplate blood-donor (slot name) (slot type))
(deffacts blood-bank ; put names & their types into [[working memory]]
          (blood-donor (name "Alice")(type "A"))
          (blood-donor (name "Agatha")(type "A"))
          (blood-donor (name "Bob")(type "B"))
          (blood-donor (name "Barbara")(type "B"))
          (blood-donor (name "Jess")(type "AB"))
          (blood-donor (name "Karen")(type "AB"))
          (blood-donor (name "Onan")(type "O"))
          (blood-donor (name "Osbert")(type "O"))
(defrule can-give-to-same-type-but-not-self ; handles A > A, B > B, O > O, AB > AB, but not N1 > N1
         (blood-donor (name ?name)(type ?type))
         (blood-donor (name ?name2)(type ?type2 &:(eq ?type ?type2) &: (neq ?name ?name2) ))
         (printout t ?name " can give blood to " ?name2 crlf)
(defrule O-gives-to-others-but-not-itself ; O to O cover in above rule
         (blood-donor (name ?name)(type ?type &:(eq ?type "O")))
         (blood-donor (name ?name2)(type ?type2 &: (neq ?type ?type2) &: (neq ?name ?name2) ))
         (printout t ?name " can give blood to " ?name2 crlf)
(defrule A-or-B-gives-to-AB ; case O gives to AB and AB gives to AB already dealt with
         (blood-donor (name ?name)(type ?type &:(or (eq ?type "A") (eq ?type "B" ))))
         (blood-donor (name ?name2)(type ?type2 &: (eq ?type2 "AB") &: (neq ?name ?name2) ))
         (printout t ?name " can give blood to " ?name2 crlf)
;(watch all)

See also[edit]

Related systems[edit]


  1. ^ a b c d e Hemmer, Markus C. (2008). Expert Systems in Chemistry Research. CRC Press. pp. 47–48. ISBN 9781420053241. Retrieved March 30, 2012. ISBN 978-1-4200-5323-4

Additional sources[edit]

External links[edit]