SCXML

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SCXML stands for State Chart XML: State Machine Notation for Control Abstraction. It is an XML-based markup language which provides a generic state-machine based execution environment based on Harel statecharts.

SCXML is able to describe complex state-machines. For example, it is possible to describe notations such as sub-states, parallel states, synchronization, or concurrency, in SCXML.

[edit] Goals

The objective of this standard is to generify state diagrams notations which are already used in other XML contexts. For example, it is expected that SCXML notations will replace the State machines notations used in the next CCXML 2.0 version (an XML standard designed to provide telephony support to VoiceXML). It could also be used as a multimodal control language in the Multimodal Interaction Activity.

One of the goals of this language is to make sure that the language is compatible with CCXML and that there is an easy path for existing CCXML scripts to be converted to SCXML without major changes to the programming model or document structure (for example, by using an XSL Transformation).

The last working draft of the specification was released by the W3C in May 2008.^[1]

[edit] Example

Here is the state chart diagram which describes the behavior of a stopwatch:

The SCXML file describing the transitions in this diagram is:

<scxml xmlns="http://www.w3.org/2005/07/SCXML"
       version="1.0"
       initialstate="ready">
    <state id="ready">
        <transition event="watch.start"   target="running"/>
    </state>
    <state id="running">
        <transition event="watch.split"   target="paused"/>
        <transition event="watch.stop"    target="stopped"/>
    </state>
    <state id="paused">
        <transition event="watch.unsplit" target="running"/>
        <transition event="watch.stop"    target="stopped"/>
    </state>
    <state id="stopped">
        <transition event="watch.reset"   target="ready"/>
    </state>
</scxml>

(Apache Licenced, see on this page)

[edit] Implementations

• Intervoice Media Exchange contains an orchestration engine which has been designed to initiate and manage media interactions. It is the industry's first commercially available product which has implemented State Chart eXtensible Markup Language (SCXML) as the framework for building complex multi-modal interactions.
• Apache Commons SCXML, a pure Java library to parse and execute SCXML diagrams
• Web interface to an experimental SCXML implementation in the Oz programming language
• Simple State Chart XML provides the first publicly available SCXML C++ implementation.

[edit] See also

• VoiceXML
• CCXML

[edit] References

[edit] External links

• W3C SCXML last working draft