SCXML

State Chart XML

Filename extension	.scxml
Developed by	World Wide Web Consortium
Latest release	7th Public working draft May 13, 2010
Type of format	Markup language
Extended from	XML
Website	http://www.w3.org/TR/scxml/

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.

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 October 2009.

Examples

According to the W3C State Chart XML (SCXML): State Machine Notation for Control Abstraction specification, SCXML is a general-purpose event-based state machine language that can be used in many ways, including:

• As a high-level dialog language controlling VoiceXML 3.0's encapsulated speech modules (voice form, voice picklist, etc.)
• As a voice application metalanguage, where in addition to VoiceXML 3.0 functionality, it may also control database access and business logic modules.
• As a multimodal control language in the MultiModal Interaction framework, combining VoiceXML 3.0 dialogs with dialogs in other modalities including keyboard and mouse, ink, vision, haptics, etc. It may also control combined modalities such as lipreading (combined speech recognition and vision) speech input with keyboard as fallback, and multiple keyboards for multi-user editing.
• As the state machine framework for a future version of CCXML.
• As an extended call center management language, combining CCXML call control functionality with computer-telephony integration for call centers that integrate telephone calls with computer screen pops, as well as other types of message exchange such as chats, instant messaging, etc.
• As a general process control language in other contexts not involving speech processing.

The W3C Voice Extensible Markup Language (VoiceXML) 3.0 specification includes State Chart and SCXML Representation to define functionality.

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Truly multimodal applications should allow the user to communicate through the interface most suitable for the context of the interaction. Consider an application that has voice as well as the mobile phones display and keyboard as interfaces. The user will favor the most effective interface and can make a voice request to avoid excessive typing and then “click” on a list or map on the display instead of listening to long descriptions of available options. SCXML makes it easy to do several things in parallel, and the Interaction Manager SCXML application will maintain the synchronization between Voice and Visual dialogues.

The W3C document Authoring Applications for the Multimodal Architecture describes a multimodal system which implements the W3C Multimodal Architecture and gives an example of a simple multimodal application authored using various W3C markup languages, including SCXML, CCXML, VoiceXML 2.1 and HTML.

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

The SCXML file describing the transitions in this diagram is:

<?xml version="1.0" encoding="UTF-8"?>
<scxml xmlns="http://www.w3.org/2005/07/scxml" version="1.0" initial="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)

Implementations

• Intervoice Media Exchange and Intervoice Voice Portal contain orchestration engines that have been designed to initiate and manage media interactions. Media Exchange and Voice Portal are the industry's first commercially available products that have implemented the World Wide Web Consortium (W3C) State Chart eXtensible Markup Language (SCXML) as the framework for building complex multi-modal interactions.
• Intervoice Interaction Composer is a graphical, Eclipse-based Integrated Development Environment (IDE) for building, deploying, and managing complex voice or multi-modal applications. Interaction Composer enables the development of applications that allow callers to perform tasks simultaneously or interrupt tasks with new requests, and then resume tasks where they left off. Interaction Composer leverages the W3C specification for State Chart eXtensible Markup Language (SCXML).
• 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 provided the first publicly available SCXML C++ implementation.
• Qt SCXML Engine implemented in C++ as well and tightly integrated with their Signals and Slots concept.
• PySCXML implemented in Python.
• SCXML4Flex ActionScript/Flex implementation.
• EclipseSCXML Eclipse Based Visual SCXML Editor.
• SCXMLgui Java Visual Editor for SCXML.

See also

• VoiceXML
• CCXML

External links

• W3C SCXML last working draft