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Standard Nears For Dynamic Web Pages
DOM describes the structure of an HTML or XML document, the relationships between components of the document, and the ways a program can access and manipulate those components. DOM is not a language specification: Unlike HTML, for example, DOM doesn't offer a full grammar and syntax. In fact, DOM interfaces are designed to be implemented in a number of different programming languages.
Like the dynamic HTML features offered in the Netscape and Microsoft browsers, DOM will allow scripts to access and modify objects in Web pages dynamically. For instance, rather than leading a user through a succession of Web pages, an author could present a user with a single page whose text and images change as the user interacts with it--perhaps by clicking on an icon. DOM expands on dynamic HTML by extending such functionality to XML documents, and by offering a standard interface that works across browsers and platforms.
The working draft released last week, which covers the "Level 1" stage of the DOM group's work, encompasses basic document navigation and manipulation. Depending on how it is received by W3C members, the paper could be the final working draft before the Level 1 specification moves toward proposed recommendation status, according to Lauren Wood, chair of the W3C's DOM working group.
"I'm pretty confident that we've got everything from Level 1 covered," she said.
Getting Into the Browsers
A "DOM Roadmap" posted on Netscape's Mozilla.org Web site, the central resource for the company's open-source software effort, states that in its current incarnation, the Mozilla source code supports some of the Level 1 core specification but does not yet support the Level 1 HTML specification.
Microsoft has yet to commit to supporting specific DOM features in Internet Explorer 5.0.
"At this point, we're working very hard to get as much of it implemented in IE 5.0 as possible," said Joe Herman, group product manager for platform marketing at Microsoft. It's still not clear how much of the specification Microsoft will be able to implement, he said, adding that Microsoft's implementation schedule depends in part on the W3C's timetable for approving the DOM specification. However, said Herman, Microsoft is committed to having the best support for standards in the industry.
Meanwhile, both browser manufacturers have been at work devising their own features for building interactive HTML pages. IE 5.0 includes a feature called DHTML Behaviors, which will let developers encapsulate scripting content in files separate from their HTML code. About six weeks ago, Microsoft submitted DHTML Behaviors to the W3C as a proposed extension to the Cascading Style Sheets standard, according to Dave Wascha, product manager for platform marketing.
Netscape last month submitted its own proposal for separating scripting content from HTML code. Under this proposal, authors would specify document behavior in "action sheets" just as they currently specify presentation in style sheets. Netscape's Byunn said the company has not yet announced support for action sheets in its own products.
Glenn Davis, chief technical officer at Project Cool, said he has mixed feelings about companies' leapfrogging of standards. Individual companies' extensions to standards often help drive innovation, he said, pointing to the evolution of HTML as one example. But companies should do their best to support existing standards in their products, he argued.
"I don't mind the innovation, as long as the things that are standard really are standard," Davis said.
While she didn't comment on Netscape or Microsoft specifically, Wood said the DOM specification represents a lot of hard work and careful thinking by experts in the field, and developers who use vendors' proprietary extensions to the standards do so possibly at the expense of interoperability and robustness.
Expanding the Web's Definition
"It's going to be likely that people are going to start using XML and DOM for things that people never see," Wood said.
IBM offers full DOM support in its XML for Java parser, according to Mike Pogue, manager of the XML technical group at IBM's Java Technology Center. Pogue said IBM is committed to continuing that support.
"We're fully compliant with DOM as it was defined in the last draft," he said. "We'll be updating the XML for Java parser to match the new DOM proposal." XML developers using IBM's parser in their applications have been using DOM features in a number of ways, Pogue said, although he demurred from commenting on the details of specific projects. The developers have been enthusiastic about the W3C's work on the DOM, he said.
"They're all very excited to see the industry coalesce around a single unified standard," Pogue said.
Wood said the latest draft of DOM differs considerably from the previous draft. For one thing, she said, the new draft contains only a core specification and an HTML specification; a standalone XML specification has been incorporated into the core document.
In addition, the working group removed interfaces for accessing XML document type definitions (DTDs). The group's work with DTDs will appear again in a working draft separate from the Level 1 DOM specification, Wood said.