1. Introduction and Requirements

1.1. Introduction

The first W3C Working Group on Synchronized Multimedia (SYMM) developed SMIL - Synchronized Multimedia Integration Language. This XML-based language is used to express synchronization relationships among media elements. SMIL 1.0 documents describe multimedia presentations that can be played in SMIL-conformant viewers.

SMIL 1.0 did not define a Document Object Model. Because SMIL is XML based, the basic functionality defined by the Core DOM is available. However, just as HTML and CSS have defined DOM interfaces to make it easier to manipulate these document types, there is a need to define a specific DOM interface for SMIL functionality. The current SYMM charter includes a deliverable for a SMIL-specific DOM to address this need, and this document specifies the SMIL DOM interfaces.

Broadly defined, the SMIL DOM is an Application Programming Interface (API) for SMIL documents and XML/HTML documents that integrate SMIL functionality. It defines the logical structure of documents and the way a document is accessed and manipulated. This is described more completely in "What is the Document Object Model".

The SMIL DOM will be based upon the DOM Core functionality (see DOM Level 2 Core). This describes a set of objects and interfaces for accessing and manipulating document objects. The SMIL DOM will also require the additional event interfaces described in the DOM Level 2 Events module. The SMIL DOM extends these interfaces to describe elements, attributes, methods and events specific to SMIL functionality.

Note that the SMIL DOM does not require support for DOM Level 2 Views, Stylesheets, CSS, Traversal, and Model Range modules.

The SYMM Working Group is also working towards a modularization of SMIL functionality, to better support integration with HTML and XML applications. Accordingly, the SMIL DOM is defined in terms of the SMIL modules.

1.2. Requirements

The design and specification of the SMIL DOM must meet the following set of requirements.

General requirements:

• Inherit DOM Level 2 core functionality - the SMIL DOM will be based upon the generic Core DOM foundation.
• Support constraints on DOM core functionality (e.g. mutation), especially at runtime.
• Support both SMIL documents as well as hybrid documents that integrate XML/HTML and SMIL functionality.
• Support and reflect the modularization of SMIL functionality. It must be possible to design hybrid documents combining XML/HTML and SMIL functionality, that can in turn support a hybrid or combined DOM.

SMIL specific requirements:

• Support SMIL specific elements. It must be possible to access and manipulate all SMIL elements within a SMIL document or a hybrid document that integrates XML and SMIL modules.
• Support SMIL specific attributes and methods. It must be possible to access and manipulate the SMIL attributes and methods on SMIL elements as well as XML/HTML elements in a hybrid documents.
• Support SMIL specific events, including:
  • Specification of statically defined SMIL events
  • Support for dynamically defined events
  • The ability to create and raise all the above events
• Support SMIL semantics. This includes various constraints on document structure, attribute values and method invocation.
• Define basic control interface for media player/renderers. Do not define a plug-in API, but rather just the timing and sync control interface.

It is not yet clear what all the requirements on the SMIL DOM will be related to the modularization of SMIL functionality. While the HTML Working Group is also working on modularization of XHTML, a modularized HTML DOM is yet to be defined. In addition, there is no general mechanism yet defined for combining DOM modules for a particular profile.