[XML-DEV Mailing List Archive Home] [By Thread] [By Date] [Recent Entries] [Reply To This Message] Re: Subtyping in XML
Jeff Lowery <jlowery@s...> writes: <snip/> > 1) Adding new value members to the value space of a type can't be any good > under any circumstances. It's possible to think up some use for such a > feature, but it would no doubt be better implemented using one of the other > mechanisms. If you mean simple type == datatype, then not only is it bad, it's not possible using W3C XML Schema. There is no derivation by extension from simple types. > 2) "Content space" refers to all specified child elements and attributes in > a type definition (there's probably a term for this already, but I've a > peasouper of mental fog today). The big fork in the road here is whether the > model group of elements is sequenced or not. > > 2a) If it's unsequenced, then addition (via extension) of new elements that > were restricted in occurrence in the supertype would likely break the bank. > For sequenced content, it seems less of a worry, taking Paul's XSLT example > as a worse case. Frankly, if you're not blocking extension of sequenced > content, you have to accept what you're given. Does that take too much > discipline? I'm the wrong person to ask, but a schema editor might support > an autoblocking configuration for complextype extension. Note here that W3C XML Schema extension is _always_ sequenced, in the sense that any member of a type defined by extension _must_ contain a member of the base type as a prefix. This property does _not_ hold for substitution groups, where type-based patterns rather than element-based ones are the only safe way to go. 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@c... URL: http://www.ltg.ed.ac.uk/~ht/ [mail really from me _always_ has this .sig -- mail without it is forged spam]
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