- From: <noah_mendelsohn@us.ibm.com>
- Date: Fri, 13 Jun 2003 16:44:10 -0400
- To: "C Baines" <cbaines@westroadchurch.org.uk>
- Cc: xmlschema-dev@w3.org
Charles Baines asks: > Which returns to the question - can <sequence> define > the order of elements by an attribute value common to > each element without having to physically list the > elements in the order required? No, <sequence> constrains the order based striclty on element name. There have been proposals to add various forms of what are collectively called co-occurrence constraints, though I haven't seen many requests for sorted sequences of the sort you suggest. Of course, there is no end to what users might want...prime numbered entries first? Sounds bizarre, but a mathematician might want it. Unless you're willing to move away from a declarative language to something Turing complete (I.e. a full programming language for the constraints), you'll always wind up trying to make reasonable tradeoffs between complexity in the schema language and its ability to express complex constraints. I think many of us have a very strong preference for retaining a language that's basically declarative, as it is so much easier to reason about and build tools for such languages. ------------------------------------------------------------------ Noah Mendelsohn Voice: 1-617-693-4036 IBM Corporation Fax: 1-617-693-8676 One Rogers Street Cambridge, MA 02142 ------------------------------------------------------------------
Received on Friday, 13 June 2003 16:45:19 UTC