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JBoss BRMS - JBoss Rules 引擎規則

JBoss Rules 第一課,
基本功我都喜歡從底層開始,這樣以後寫起來會事半功倍。
所以要看一下這個語言是如何執行的。

JBoss Rules 基本上就是去撰寫一堆的邏輯,然後把收集的資料(Fact)放進去,執行出來的就是結果囉!


因為同時會有很多人在會在上面執行,JBoss Rules 引擎也不可能把大家丟進去的物件全部搞在一起。所以引擎必須要將每個使用者的獨立的位置去存放每個人的Fact。這個空間我們叫它Working memory. 所有在JBoss Rule裡面對於Fact的修改,全部都會在自己的Working memory 做。當你的Fact 因為條件而有所變動時的名詞叫做 Truth Management. 我們建制的規則則被讀取,然後放進引擎的RuleBase。


每次執行的時候,JBoss Rules 引擎就會開始看哪些規則可以被執行,這些符合資格可以被執行的規則就叫做Agenda, 然後決定要執行這些規則順序。被執行的規則就叫做Activation。
例如說,有一堆規則在RuleBase裡面如下,


然後,這次input進去的Fact內容如下,


所以JBoss Rules 引擎就會把可以執行的Rules先找出來,跑出來的Agenda如下面藍色底色的規則



但是這些Agenda 確定執行的順序決定方式如下,也有個名字叫做 Conflict resolution. 衝突管理。


所謂的Salience 就是你在 JBoss Rules 一開始的設定的執行順序,數字越大,表示順序越高。(可以是負數)




如果沒有特別設定,而且排序相同時,他就會看一下這些規則有哪些最近常常被跑到的,會以這個為優先, 如果這些規則的執行次數都差不多的時候,他就會看這些執行規則的複雜程度。越複雜的優先。如果真的不幸每個規則都是一樣複雜的話。那就只好靠誰先load 進來誰就先執行了。

以上為執行的方式。至於計算的演算法。JBoss Rules 是用 RETE. 有機會再上來寫吧!







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