xdocs/guide/custom-semantics.xml - commons-scxml - Git at Google

 <?xml version="1.0" encoding="UTF-8"?>
 <!--
  * Licensed to the Apache Software Foundation (ASF) under one or more
  * contributor license agreements.  See the NOTICE file distributed with
  * this work for additional information regarding copyright ownership.
  * The ASF licenses this file to You under the Apache License, Version 2.0
  * (the "License"); you may not use this file except in compliance with
  * the License.  You may obtain a copy of the License at
  *
  *     http://www.apache.org/licenses/LICENSE-2.0
  *
  * Unless required by applicable law or agreed to in writing, software
  * distributed under the License is distributed on an "AS IS" BASIS,
  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  * See the License for the specific language governing permissions and
  * limitations under the License.
 -->

 <document>

  <properties>
   <title>Using custom semantics for the Commons SCXML engine</title>
   <author email="dev@commons.apache.org">Commons Documentation Team</author>
  </properties>

  <body>

   <section name="SCXML Semantics">

    <p><b>This section is for advanced users only, and will probably not
    be needed by most users of the Commons SCXML library.</b></p>

    <subsection name="Pluggable semantics">

     <p>The Commons SCXML state machine engine is really a tuple, the
     <a href="../apidocs/org/apache/commons/scxml/SCXMLExecutor.html">SCXMLExecutor</a>
     (an API that new users can code to, and is almost always sufficient)
     accompanied by a
     <a href="../apidocs/org/apache/commons/scxml/SCXMLSemantics.html">SCXMLSemantics</a>
     implementation (an API that advanced users can code to, to change the
     engine behavior to suit their needs).</p>

     <p>The basic modus operandi for an engine is simple - when an event is
     triggered, figure out which (if any) transition(s) to follow, and
     transit to the new set of states executing any specified actions along
     the way. The default semantics available in the Commons SCXML distribution
     can be replaced with custom semantics provided by the user using the
     <code>SCXMLExecutor</code> constructor that takes the
     <code>SCXMLSemantics</code> parameter i.e. the engine semantics are
     "pluggable".</p>

    </subsection>

    <subsection name="Example scenario">

     <p>Consider dispute resolution for example -- when more than one
     outbound transitions from a single state hold true. The default
     <code>SCXMLSemantics</code> implementation available in the distribution
     does none, it will follow all filtered transitions, possibly leading to a
     <code>ModelException</code> immediately or down the road. However, a user
     may want:</p>

     <ul>
      <li>The transition defined closest to the document root to be
      followed</li>
      <li>The transition defined farthest from the document root to be
      followed</li>
      <li>The transition whose origin and target have the lowest common
      ancestor to be followed</li>
      <li>The transition whose origin and target have the highest common
      ancestor to be followed</li>
     </ul>

     <p>Even after one of above dispute resolution algorithms is applied, if
     there are more than one candidate transitions, the user may want:</p>

     <ul>
      <li>A <code>ModelException</code> to be thrown</li>
      <li>The transition that appears first in document order to be
      followed</li>
      <li>The transition that appears last in document order to be
      followed</li>
     </ul>

     <p>To implement any of the above choices, the user may extend the
     default <code>SCXMLSemantics</code> implementation, override the
     <code>filterTransitionsSet()</code> method (or write a new implementation
     from scratch), and plug in the new semantics while instantiating the
     <code>SCXMLExecutor</code>. The pluggability allows differing semantics
     to be developed for the Commons SCXML engine, independent of the Commons
     SCXML codebase.</p>

    </subsection>

   </section>

  </body>

 </document>
	<?xml version="1.0" encoding="UTF-8"?>
	<!--
	* Licensed to the Apache Software Foundation (ASF) under one or more
	* contributor license agreements. See the NOTICE file distributed with
	* this work for additional information regarding copyright ownership.
	* The ASF licenses this file to You under the Apache License, Version 2.0
	* (the "License"); you may not use this file except in compliance with
	* the License. You may obtain a copy of the License at
	*
	* http://www.apache.org/licenses/LICENSE-2.0
	*
	* Unless required by applicable law or agreed to in writing, software
	* distributed under the License is distributed on an "AS IS" BASIS,
	* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
	* See the License for the specific language governing permissions and
	* limitations under the License.
	-->

	<document>

	<properties>
	<title>Using custom semantics for the Commons SCXML engine</title>
	<author email="dev@commons.apache.org">Commons Documentation Team</author>
	</properties>

	<body>

	<section name="SCXML Semantics">

	<p><b>This section is for advanced users only, and will probably not
	be needed by most users of the Commons SCXML library.</b></p>

	<subsection name="Pluggable semantics">

	<p>The Commons SCXML state machine engine is really a tuple, the
	<a href="../apidocs/org/apache/commons/scxml/SCXMLExecutor.html">SCXMLExecutor</a>
	(an API that new users can code to, and is almost always sufficient)
	accompanied by a
	<a href="../apidocs/org/apache/commons/scxml/SCXMLSemantics.html">SCXMLSemantics</a>
	implementation (an API that advanced users can code to, to change the
	engine behavior to suit their needs).</p>

	<p>The basic modus operandi for an engine is simple - when an event is
	triggered, figure out which (if any) transition(s) to follow, and
	transit to the new set of states executing any specified actions along
	the way. The default semantics available in the Commons SCXML distribution
	can be replaced with custom semantics provided by the user using the
	<code>SCXMLExecutor</code> constructor that takes the
	<code>SCXMLSemantics</code> parameter i.e. the engine semantics are
	"pluggable".</p>

	</subsection>

	<subsection name="Example scenario">

	<p>Consider dispute resolution for example -- when more than one
	outbound transitions from a single state hold true. The default
	<code>SCXMLSemantics</code> implementation available in the distribution
	does none, it will follow all filtered transitions, possibly leading to a
	<code>ModelException</code> immediately or down the road. However, a user
	may want:</p>

	<ul>
	<li>The transition defined closest to the document root to be
	followed</li>
	<li>The transition defined farthest from the document root to be
	followed</li>
	<li>The transition whose origin and target have the lowest common
	ancestor to be followed</li>
	<li>The transition whose origin and target have the highest common
	ancestor to be followed</li>
	</ul>

	<p>Even after one of above dispute resolution algorithms is applied, if
	there are more than one candidate transitions, the user may want:</p>

	<ul>
	<li>A <code>ModelException</code> to be thrown</li>
	<li>The transition that appears first in document order to be
	followed</li>
	<li>The transition that appears last in document order to be
	followed</li>
	</ul>

	<p>To implement any of the above choices, the user may extend the
	default <code>SCXMLSemantics</code> implementation, override the
	<code>filterTransitionsSet()</code> method (or write a new implementation
	from scratch), and plug in the new semantics while instantiating the
	<code>SCXMLExecutor</code>. The pluggability allows differing semantics
	to be developed for the Commons SCXML engine, independent of the Commons
	SCXML codebase.</p>

	</subsection>

	</section>

	</body>

	</document>