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From Apache Wiki <wikidi...@apache.org>
Subject [Jakarta-commons Wiki] Update of "SCXML/FrequentlyAskedQuestions" by RahulAkolkar
Date Tue, 14 Feb 2006 22:09:24 GMT
Dear Wiki user,

You have subscribed to a wiki page or wiki category on "Jakarta-commons Wiki" for change notification.

The following page has been changed by RahulAkolkar:
http://wiki.apache.org/jakarta-commons/SCXML/FrequentlyAskedQuestions

The comment on the change is:
New entry about contexts and evaluators (from Tim O'Brien's FAQ suggestions)

------------------------------------------------------------------------------
  [[TableOfContents]]
  
  ----
+ 
+ ==== What is a Context? And what is an Evaluator? ====
+ 
+ The SCXML specification allows an implementation to support multiple expressions languages.
These expressions become part of attribute values for executable content, such as:
+ 
+ {{{
+ <var name="foo" expr="1 + 2 + bar" />
+ }}}
+ 
+ or are used to evaluate the boolean guard conditions that decide whether or not a particular
transition is followed once its associated trigger event is received, such as:
+ 
+ {{{
+ <transition event="day.close" cond="day eq 'Friday'" target="weekend" />
+ }}}
+ 
+ In order to support multiple expression languages, Commons SCXML uses two interfaces which
serve as adapters to the APIs for the particular expression language used for a particular
SCXML document.
+ 
+  * The ''Context'' is a collection of variables that defines a variable "scope". Each <state>
element within an SCXML document gets its own ''Context'' or variable scope.
+ 
+  * The ''Evaluator'' is a component with the capability of parsing and evaluating expressions.
It is the "expression language engine".
+ 
+ Commons SCXML currently provide implementations for [http://jakarta.apache.org/commons/sandbox/scxml/apidocs/org/apache/commons/scxml/env/jexl/package-summary.html
JEXL] and [http://jakarta.apache.org/commons/sandbox/scxml/apidocs/org/apache/commons/scxml/env/jsp/package-summary.html
JSP 2.0 EL].
  
  ==== How do I try out the sample SCXML documents? ====
  

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