Last Word on Last Call
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•Background |
Schemas are now beyond "last call," soon to go to Candidate Recommendation. GCA?s XML Europe conference presented the opportunity to speak with implementers about how the specification looks as it looms on the horizon. The subsequent publication of the comment archive presented a further opportunity to read the mood of the developer community, and confirmed that there are major points of contention over the draft.
While some implementers outside the W3C process do not see impediments in the last call draft, from my brief survey, these folks tend not to be looking to use the new features of schema or to write the reference implementations. For them, the schema draft represents DTD-in-XML-syntax with datatypes, and if the rest of it has issues, they don?t care. Among the others, who also support the W3C effort, there are those who wish for some changes. The most-desired changes are to reduce the feature set, with an eye toward reducing complexity of design, and to do a major rewrite so that simple things are not rendered hard, and hard things not made harder. Among those who take issue with the draft, the most favored outcome is universally viewed unlikely to happen: release of the data types part of the specification along with a DTD for schemas replicating DTD functionality, and more time to sort the rest of it out.
Background
The opening shots in the campaign for schemas were fired in December 1997. XML 1.0 itself was not yet a Recommendation, but it was already clear to careful observers that XML was going to play a crucial role in database interoperability and e-commerce, as well as the literary and publishing work targeted by most SGML applications. At GCA?s XML/SGML ?97, the draft specification of XML 1.0 was handed out, and François Chahuneau and Henry Thompson each delivered papers on the requirement for schemata that would transcend the limitations of DTDs. The WG was formed shortly thereafter, but didn?t really get down to cases until after the entire W3C XML Activity was reorganized in August 1998. Calls for completion started even before the current WG convened.
Microsoft, with co-authors Henry Thompson of the University of Edinburgh and others from Arbortext, Inso, and DataChannel, had published XML-Data in late 1997. It was submitted as a Note to the W3C on January 5, 1998, in time to present it as a fait accompli to a standing-room only crowd at a GCA XML Conference tutorial in March, 1998. Later, CommerceOne submitted Schema for Object-Oriented XML 2.0 (SOX) as a Note. Between the submission of the first Note and the end of last call comments, barely two years have elapsed. In comparison, Charles Goldfarb cites 17 years for the development of the semantics of DTDs and markup declaration syntax, from 1969 through 1986. Ten years of experience with markup applications made it possible to narrow the scope for instance syntax and grammar, but it has greatly broadened the scope for the corresponding schema.
Consider the task of the current WG: to create a common framework for abstracting all information, regardless of the form (be it narrative, normalized data, objects, or multi-media) and regardless of domain (be it historical, literary, mathematical, financial, or strategic). Wherever you attempt to draw a line and say "schemas don?t have to model this," someone else will come back and say, "no, that information and that model are mission-critical for my implementation."
Here are the milestones leading up to the current draft:
- XML-Data submission -- January 5, 1998
- SOX submission -- September 30, 1998 (updated July 7, 1999)
- Schema requirements -- February 15, 1999
- Draft specifications -- February 25, 2000; December 17, November 5, September 24, May 6 of 1999
- Last-call draft -- April 7, 2000.
The prior release of XML 1.0, the clear signs that XML was taking off for a wide range of applications, and the release of XML-Data formed the parameters within which XML schemas have been created. The pressure was on the WG from day one to produce a spec quickly that met or exceeded the functionality of the Microsoft draft, and to do so in a large committee with representation from all the heavy lifters of the database and structured document world.
The current draft has elicited over 200 comments from individuals around the world. The opening up of the comment archive indicates not only the significance of this specification, but the degree of care and responsibility with which its development has been handled both inside and outside the W3C.
Vox Populi
Based on my casual survey in Paris, and some follow-up work, the community seems to be fairly evenly divided along these lines:
Positive, will implement:
"It was a long time coming, but in my view it looks good. It puts the same representation on XML as I can do in code? It maps to the way object oriented programmers would think, which is good."
Of the positive respondees, one has the caveat that they won't do the heavy lifting, but will wait for reference/open source implementations (parsers) and as a result, they expected schema to have little impact on their resources. While this group reports that customers are asking about schema, they do not expect it to impact product functionality.
Fairly indifferent, doesn't affect development plans:
This is the response of several vendors who are tracking the spec, but who feel that their product is not reliant on schema functionality. They report that their customers are more involved in "real world" issues and have their plate full with plain XML migration. In their view, schema is a refinement important to a hardcore group of XML users, but not essential for the mainstream of their market. This group, of course, is more on the document side than the data side of XML application.
Negative, wish they would fix it before release:
Of the negatives, Praxis has the greatest dependency on the final schema spec, and CTO Matthew Gertner was willing to go on the record. Their application, Schemantix, sucks in schemas and spits out HTML forms for editing conformant XML instances. Obviously, schemas are their life-blood. Right now, they use SOX, the schema language from Commerce One, but they expect to adopt the W3C Recommendation. Gertner has commented formally and informally to the W3C on their view of the complexity and overkill of the draft spec.
The best indication of how the affected developer community feels, of course, is contained in the comments on the April draft, although this archive necessarily reflects on that segment that would like to see changes made. Among those, the sentiments expressed indicate that a significant segment of the community dedicated to open standards wants W3C XML schema to succeed, but would like to turn back the clock and take one more shot at a cleaner design and exposition.
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