Re: Elements order:
Christopher R. Maden wrote: > Yes. SGML had an "and" connector: > <!ELEMENT data - - (name & surname & age & gender)> > would require exactly one each of name, surname, age, and gender, in any orde > r. > > However, there were concerns that the way SGML mandated the interpretation > of this content model was not easily implemented. This capability, without > SGML's restrictions, is back in Schemas. AIUI, W3C XML Schema places even *more* restrictions on 'all' groups than SGML does for '&' groups. If I'm interpreting the Rec correctly, it doesn't allow <xsd:all> groups to be used inside other model groups, and the members of an <xsd:all> group are limited to single elements (optionally optional). The main trouble with '&' groups in SGML is that they aren't *quite* what's needed in the case of repeatable subelements. For example, in SGML: <!ELEMENT HEAD - - (TITLE & BASE? & LINK* & META*) > allows the sequences 'TITLE,LINK,LINK,META' and 'TITLE,META,LINK,LINK', but not 'TITLE,LINK,META,LINK'. Specifying the desired content model is rather tricky even with '&' groups. TREX (and RELAX-NG?) have a more powerful (and simpler!) 'interleave' operator which does the right thing for this sort of case. It's not hard to express in Schematron either. I don't think this construct is even possible to specify with W3C XML Schemas (though I may be mistaken). --Joe English jenglish@f...
PURCHASE STYLUS STUDIO ONLINE TODAY!
Purchasing Stylus Studio from our online shop is Easy, Secure and Value Priced!
Download The World's Best XML IDE!
Accelerate XML development with our award-winning XML IDE - Download a free trial today!
Subscribe in XML format