STEVENSON, Wash—Its always refreshing to attend a deeply technical conference, at which the experts instruct each other, disagree publicly and challenge one anothers opinions. Instead of showing off shiny new functionality or imperfect features polished to a mirror surface, the developers at the Applied XML Developers Conference are demonstrating the problems yet to be solved in XML and Web services.
Still, the technical presentations make it clear that they agree on fundamental development truths: The data outlasts the code, you wont find much reality in any industry spec, and simplicity is always better than (even elegant) complexity.
One weakness upon which most presenters agree is the ineffectiveness of XML Schema, which Tim Bray, director of Web technologies at Sun Microsystems (and co-inventor of XML), described as “totally beyond its sell by date.”
Chris Anderson, an architect on the MS Windows client platform team working on the technologies code-named “Avalon,” said developers “hate systems that force XML to be more than data.” His answer: XAML (Extensible Application Markup Language), which “provides a format to facilitate between developers and designers … a unified way to build applications to leverage markup.”
Sam Ruby, senior technical staff member in the Emerging Technologies group at IBM, spent 45 minutes showing other experts how “the standards dont reflect reality; reality has moved on,” particularly in regard to Unicode. Even when default encodings for HTML, XML and Microsoft are different, and XML Namespaces requires that the URI examples be considered distinct,
Not every aspect of XML is judged to be a potential disaster—far from it. Two presentations have demonstrated how XML is enabling solutions in the real world: one from the U.S. Department of Defense on using XML for Navy missile systems, and a presentation from Scott Hanselman and Patrick Cauldwell of Corillian about effectively using XML in financial systems.
-Term Results?”> Some XML technologies have yielded long-term results, or they will. “We had pretty ambitious goals for SOAP [Simple Object Access Protocol],” said Don Box, a Microsoft architect in the Distributed Systems group working on Indigo.
“The one thing we wanted was an extensibility mechanism other than XMLs throw [stuff] anywhere you want.” Today, Box said, SOAPs header extensibility model is the conceptual basis for the serialization engine for .NET.
Yet “the single most important thing we [previously] left out was WS-Mex [metadata exchange] or something like it,” Box said. Its now a core part of Indigo, and “every SOAP endpoint will support WS-Mex by 2007.”
And theres plenty of dissent among the experts, none of whom are shy with their opinions. Even when they agree on the problems, they dont always agree on the solutions, with the sharpest division between those who prefer APIs and programming models versus data streaming.
“WS-Eventing is missing the boat,” Bray said. “If this entire experiment fails, I think the fingerprints [on the knife] will be on WSD and XSD,” Box commented.
But each speaker had an underlying theme of “keep it simple.” Bray exhorted developers to create solutions based on the MPRDV approach: the “minimum progress required to declare victory.” Add functionality only when you have to, and based on real experience, he said. “Committees going into rooms do not invent the future,” he said. Anderson reminded developers that “XML is cardboard”—the transport medium for the “important stuff” youre moving from place to place.
Thats not to say that developers are down on XML—not hardly! These folks are the ones immersed in the technology and clearing the path for those to follow. “Theyre shining the light in the dark corners,” remarked one conference attendee. Because of the technology sharing, one long-outstanding bug that IBMs Ruby demonstrated on the MSDN site was fixed within two hours.
Despite XMLs imperfections, each presenter saw the benefits that XML and Web services have brought, from RSS (Really Simple Syndication) ubiquity to interoperability to the importance of internationalization. On her blog, Rebecca Dias, product manager for advanced Web services at Microsoft, said, “Everyone generally agrees that schema has its shortcomings, but it is facilitating huge amounts of value for customers. Thousands of business documents today are based on a schema. So, is XML Schema a failure?”