Jess程序设计语言

Jess是Java平台上的规则引擎，它是CLIPS程序设计语言的超集，由Sandia国家实验室的Ernest Friedman-Hill开发。它的第一个版本写于1995年晚期。

It provides rule-based programming suitable for automating an expert system, and is often referred to as an expert system shell. 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.

Jess can be used to build Java servlets, EJBs, applets, and full applications that use knowledge in the form of declarative rules to draw conclusions and make inferences. Since many rules may match many inputs, there are few effective general purpose matching algorithms. The Jess rules engine uses the Rete algorithm.

许可证

Jess不是开源软件，而CLIPS是。

代码实例

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:

(clear)
(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)
(reset)
(run)

参见

JSR-94

外部链接

官方网站