xml-dev - RE: ATTLIST question

[Steve Rowe <sarowe@textwise.com>]

James Gray wrote:
> I'm trying to create a DTD that will incorporate an 
> attribute list that will allow  the following case:
> 
>   1. Define optional values for an element
>   2. Require one of the options be present
>   3. Not allow any option other than those listed
> 
> I've scoured my XML books and can't figure out how
> to implement such a case.  An example that is 
> similar is for shirts.  I'd like to have a "shirt"
> element that is only allowed to the values:
> S, M, LG, XL
> 
> If the <shirt> element is filled with "XS" or "XXL",
> I would be able to reject it based on my DTD?

Yes, you would, with a validating parser.  A possible
DTD fragment to get what you want, using enumerated
attribute values and requiring the "size" attribute
for shirt elements:

  <!ELEMENT shirt EMPTY>
  <!ATTLIST shirt size (S|M|LG|XL) #REQUIRED>

Tim Bray says of enumerated attribute values: "You'll
see a lot of this in real-world XML documents" [1]

Hope it helps.
Steve Rowe
MNIS-TextWise Labs

[1] The Annotated XML Specification
    <URL:http://www.xml.com/axml/testaxml.htm>
    In Section 3.3.1 (Attribute Types), at the
    (T)echnical note to the Enumeration validity
    constraint:
    <URL:http://www.xml.com/axml/notes/EnumAttr.html>