- From: Henry S. Thompson <ht@cogsci.ed.ac.uk>
- Date: 16 Dec 2002 11:06:17 +0000
- To: Hans Teijgeler <Hans.Teijgeler@inter.nl.net> (by way of "C. M. Sperberg-McQueen" <cmsmcq@acm.org>)
- Cc: W3C XML Schema Comments list <www-xml-schema-comments@w3.org>
Hans Teijgeler <Hans.Teijgeler@inter.nl.net> (by way of "C. M. Sperberg-McQueen" <cmsmcq@acm.org>) writes: > In that data model, written in EXPRESS, we see entity types that are > the subtype of more than one other entity type, i.e. we have multiple > (attribute) inheritance. We have represented the entire data model in > XML Schema, with one exception: that multiple inheritance, because it > appears to us that XML Schema cannot handle that. As it stands, W3C XML Schema type derivation does not support multiple inheritance. <snip/> > I seek a workaround for this problem, that not only allows me to > inherit all 2+2 attributes, but also let 'child' be a true subtype of > both 'parent_1' AND of 'parent_2'. The only available workaround, to use named attribute groups, does not give you the derivation ('subtype') relations you desire, sorry. > The latter is important in cases where a key-keyref Identity > Constraint in the XML Schema 'refer's to, for example, 'parent_2' and > where in the derived XML file reference is made to an instance of > 'child' (which should pass validation). This isn't (yet) a good reason for needing multiple inheritance, since the usage you describe won't work with key/keyref field or selector paths, since they are interpreted per XPath 1.0 which does not know about substitution groups or type-based matching. With XPath 2.0, the situation may change for the better in this regard. ht -- Henry S. Thompson, HCRC Language Technology Group, University of Edinburgh W3C Fellow 1999--2002, part-time member of W3C Team 2 Buccleuch Place, Edinburgh EH8 9LW, SCOTLAND -- (44) 131 650-4440 Fax: (44) 131 650-4587, e-mail: ht@cogsci.ed.ac.uk URL: http://www.ltg.ed.ac.uk/~ht/ [mail really from me _always_ has this .sig -- mail without it is forged spam]
Received on Monday, 16 December 2002 06:06:13 UTC