- From: Robert Tiess <rjtiess@warwick.net>
- Date: Mon, 26 Feb 2001 23:51:46 -0500
- To: xmlschema-dev@w3.org
"Henry S. Thompson" wrote: > No, it's a real bug, now fixed but not released. Thanks for verifying that. Just wondering. "Henry S. Thompson" wrote: > Nothing in an XML Schema implementation should > be order dependent, since nothing in XML Schema > itself is. I understand and agree concerning implementation. Yet, while the example we dealt with illustrates order independence of XML Schema, there are, as we know, obvious needs within schema structures for order such that implementation (say a third party validating schema parser) enforces order, as in the clear case of model groups (sequences, namely) or other statements in XML Schema docs, such as XML Schema Part 0: "Primer, 2.5.2 Mixed Content" ("Under the XML Schema mixed model, the order and number of child elements appearing in an instance must agree with the order and number of child elements specified in the model") and XML Schema Part 1: Structures: "Constraint on Schemas: Particle Derivation OK (All:All,Sequence:Sequence -- Recurse)": "Although the validation semantics of an all group does not depend on the order of its particles, we require derived all groups to match the order of their base to simplify checking that the derivation is OK." XML Schema Part 2: Datatypes "2.5.1.3 Union datatypes" also suggests implementational significance of order: "The order in which the memberTypes are specified in the definition (that is, the order of the <simpleType> children of the <union> element, or the order of the QNames in the memberTypes attribute) is significant. During validation, an element or attribute's value is validated against the memberTypes in the order in which they appear in the definition until a match is found." Omniscience should be attainable in hypothetical schema applications upon receipt of a valid and well-formed schema, so complexTypes occurring before or after element declarations are resolved respectively; omniscient yet scoping validators. Beyond this, stylistic, logical, and organizational issues arise. In terms of clarity, the XML Schema doc examples provide excellent models for breaking down complex structures into legible units. The freedoms Schema endows are many and wonderful, provided implementations will competently parse them and the schemas themselves will have been clearly conceived, complex only as was necessary to accommodate their anticipated data. Robert Tiess rjtiess@warwick.net http://rtiess.tripod.com
Received on Monday, 26 February 2001 23:42:42 UTC