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[XML-DEV Mailing List Archive Home] [By Thread] [By Date] [Recent Entries] [Reply To This Message] RE: Re: determining ID-ness in XML
 At 8:22 AM -0500 10/31/01, Champion, Mike wrote: >> >> xml:id and/or xml:idatts >> can be layered on top of XML 1.0 without changing anything >> about XML 1.0. > >What does "without changing anything about XML 1.0" mean, exactly? Simply this: all existing tools continue to work on documents that contain xml:id attributes without any changes. They continue to do the same things they do with those documents they do today. >Could the >xml+id processor be actually layered on top (or in front of) an XML 1.0 >processor without changing the DTD validation logic? Absolutely. A valid document must declare xml:id, just like it has to declare xml:lang, xml:base, and xml:space. An invalid document doesn't have to declare these. >Does it mean that >valid and well-formed XML 1.0 documents will continue to be so in xml+ids? Absolutely. >How about schema processors; will an "old" schema processor interoperate >with an xml+ids XML processor? > Certainly. It's the same story as with DTDs. A schema-valid document must declare xml:id, just like it has to declare xml:lang, xml:base, and xml:space. An invalid document doesn't have to declare these. >One question (brought up by Michael Kay in an internal discussion): "is >xml+id" non-uniqueness a well-formedness error, or will it be some sort of >low-level validation error? Presumably a well-formedness error, since >non-validating parsers have no notion of "validation". This is the one tricky part. It is neither a well-formedness error nor a validity error. It is violation of the xml:id specification, but is in no way a violation of XML 1.0, Namespaces in XML, or Schemas. Parsers would not, at least by default, report such a violation unless a DTD or schema declared that xml:id had type ID, in which case it becomes a normal XML 1.0 or schemas validity error. It would be an error equivalent to xml:base="^^^^" or anything else that is not a legal URI. That is, it is not an XML 1.0 error. The XML parser will generally not flag this. A client application that was aware of the extra semantics attached to xml:id would catch the problem, much like an XLink processor would catch a problem with the above xml:base attribute but a normal XML parser would not. >BUT if there is a >schema-defined ID and a XML+id-defined ID that clash, it is presumaby a >validity error, because schemas only apply to well-formed XML documents ... >andy anyway this implies that the schema processor knows about xml+id. > Also tricky. I propose that xml:id defines its own ID space which is unique among other xml:id attributes but not necessarily among all ID type attributes. XPointers and other xml:id aware specs would define a rule for which type of ID wins in the event of a conflict. >These potential complications seem to suggest that doing any more than the >bare minimum could start to get hairy. I'm inclined against adding ISO >entities, multiple ids/element, namespace support, etc. in the first >iteration. > I don't know. I agree that entities really aren't relevant here or a good idea because that would break XML 1.0. However, it seems that everything I've said here about xml:id works equally well for xml:idatts. -- +-----------------------+------------------------+-------------------+ | Elliotte Rusty Harold | elharo@m... | Writer/Programmer | +-----------------------+------------------------+-------------------+ | The XML Bible, 2nd Edition (Hungry Minds, 2001) | | http://www.ibiblio.org/xml/books/bible2/ | | http://www.amazon.com/exec/obidos/ISBN=0764547607/cafeaulaitA/ | +----------------------------------+---------------------------------+ | Read Cafe au Lait for Java News: http://www.cafeaulait.org/ | | Read Cafe con Leche for XML News: http://www.ibiblio.org/xml/ | +----------------------------------+---------------------------------+ 
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