- From: Eve L. Maler <Eve.Maler@east.sun.com>
- Date: Tue, 30 May 2000 13:27:46 -0400
- To: www-xml-schema-comments@w3.org
- Cc: w3c-xml-linking-wg@w3.org
[I really apologize for the delay in sending these. I thought I had sent them last week, and noticed just now that I hadn't.] XML Linking Working Group Comments on the XML Schema last-call specifications 26 May 2000 XML Linking Working Group is a potential user of the XML Schema specifications because its XLink vocabulary has constraints that are useful to express in a schema. Therefore, we have concentrated our review of the XML Schema specifications on whether they have the ability to express XLink's current needs and anticipated future needs. The Last Call version of XLink appears to be quite expressible in XML Schema. For example, Jonathan Marsh has written a schema that does a good job of covering the constraints in the XLink spec. [1] Since each XLink-significant attribute has a fixed name, the name can simply be declared as the attribute name in the schema, for example, <xlink-prefix>:href. However, our group has been asked to allow XLink users to design their own names for attributes that have XLink-specified meaning so that, for example, the XHTML <img> element can have an attribute called src that serves the purpose of an XLink href attribute. We hope to meet this request in the future development of XLink, and expect that XML Schema can help. For example, we could define a simple type called "XLink-href", and simply require that an attribute of this type be present when referencing needs to be done in XLink, no matter what name the attribute actually has. While it is an easy matter to define such simple types, we found that there is no way for an XML Schema to package the desired attributes of the desired types; for example, the fact that a simple linking element needs optional "XLink-href", "XLink-role", etc. attributes would have to be expressed in prose, not in a schema. Thus, a normative schema module for this imagined future XLink spec would consist only of some simple-type definitions; users of the module, once they decided on their desired attribute names, would have to do the work of writing a schema that adhered to the additional constraints. The Linking group thus requests that the Schema group consider the addition of a feature that would allow the specification of "any attribute of the xxx type," or something similar, in an attribute-list declaration. One experiment using the <anyAttribute> element has been produced along these lines [2]; another approach could be to create attribute equivalence classes. A large majority of the Linking group felt that this new feature should be a Version 2 XML Schema work product; one person felt instead that it should be added to Version 1, on the grounds that it would take too long if we depended on the completion of an XML Schema Version 2 effort before publishing a normative XLink schema using this feature (given that XLink Version 1 is ahead of the development curve of XML Schema Version 1). Since XLink might be called an "enabling vocabulary" rather than a complete application on its own, we believe that this new functionality is important for letting XLink users design a higher-level markup language on their own terms. With this feature available, we expect that other enabling vocabularies focusing on types rather than markup names might arise. Given the promise of intelligent processing inherent in the XML Schema typing system, we feel that this would strengthen XML Schema's usefulness. Thank you for your consideration. Eve Maler for the XML Linking Working Group [1] http://www.w3.org/XML/Group/2000/05/xlink-schema/datatypes.dtd http://www.w3.org/XML/Group/2000/05/xlink-schema/structures.dtd http://www.w3.org/XML/Group/2000/05/xlink-schema/versioninfo.ent http://www.w3.org/XML/Group/2000/05/xlink-schema/XLink.xsd http://www.w3.org/XML/Group/2000/05/xlink-schema/mylink.xsd [2] http://lists.w3.org/Archives/Member/w3c-xml-linking-ig/2000May/0061.html http://lists.w3.org/Archives/Member/w3c-xml-linking-ig/2000May/0062.html -- Eve Maler +1 781 442 3190 Sun Microsystems XML Technology Center elm @ east.sun.com
Received on Tuesday, 30 May 2000 13:27:26 UTC