- From: <noah_mendelsohn@us.ibm.com>
- Date: Mon, 4 Apr 2005 22:42:33 -0400
- To: Robin Berjon <robin.berjon@expway.fr>
- Cc: www-tag@w3.org
Robin Berjon writes: > And is it not one of the greatest ironies of XML > Schema that it failed to learn from that lesson > and therefore didn't provide simple and > straightforward means to describe extensibility in > schemata? It is indeed, though to be fair, there was and to some degree still is a great deal of disagreement as to what evolution strategies people wanted to use for their instances. The job of schema is to make it easy to describe evolving constraints on those instances, and the community was nowhere near consensus on what idioms were to be described. For example, there was strong belief on the part of some that even a small change (bug fix?) to a language would result in complete republication putting either (a) the entire language into a new namespace or (b) at minimum the new constructs into a new namespace. We have since seen important XML languages that do neither (a) nor (b). In 1999, I suggested to the XML plenary that the XML community as a whole should consider just these questions [1], in part so that XML schema would have a context in which to explore the requirements. The response from the CG was basically: versioning is a known hard problem and if we try to tackle it, we'll spend more time and energy than we can afford. Let's not try now. I don't think it's fair to blame only the Schema WG for that decision. Note that the current schema wg charter specifically makes versioning a priority [2], and a very serious effort is being made to explore use cases and requirements, and then to develop suitable support in Schema 1.1. So, ironic as it may appear now, there was a conscious decision by the CG not to make a frontal assault on versioning for the community as a whole. There were scattered attempts be Schema WG members to add features that might be helpful. Wildcards, substitution groups and the <redefine> mechanisms are all examples of mechanisms that provide at least limited support for certain versioning idioms. The WG is now, belatedly, involved in a much more serious attempt to understand the requirements and to define more robust mechanisms to support versioning. Noah [1] http://lists.w3.org/Archives/Member/w3c-xml-plenary/1999Oct/0019.html [2] http://www.w3.org/2003/09/xmlap/xml-schema-wg-charter.html#Deliverables -------------------------------------- Noah Mendelsohn IBM Corporation One Rogers Street Cambridge, MA 02142 1-617-693-4036 --------------------------------------
Received on Tuesday, 5 April 2005 02:42:45 UTC