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[XML-DEV Mailing List Archive Home] [By Thread] [By Date] [Recent Entries] [Reply To This Message] Re: canonicalization
 >Elliotte Rusty Harold wrote: >But isn't this difference more historical than technical? > No, it's completely technical, not at all historical. Entities don't have a fallback mechanism. XInclude does. It's irrelevant which one was defined first. The fallback mechanism makes canonicalization an unpredictable operation on the post-include infoset, which is exactly what canonicalization is trying to avoid. >If you build an application on XInclude, you will want this inclusion >to be as transparent as possible and the document before XInclude >may be meaningless, as meaningless as a XML document without its >external parsed entities. In both case, you can generate *a* XPath >data model and this data model is not appropriate in either case and >is not *the* XPath data model of the merged document. That's not true. You most certainly can build an XPath data model for an unmerged document that has some xinclude:include elements. You cannot build such a data model for a document in which the external entities are not resolved. The XPath data model only applies to documents in which all external entities are resolved. So the two cases are *not* the same. Furthermore, both unmerged documents do have meaning. Theya re not meaningless. For instance, imagine a book in which the individual chapters are referenced by either XInclude or external entities. Even without resolving those entities this document may contain useful information, such as the table of contents. >I wonder if we do not see external parsed entities as "more core" >than XInclude just because we are used to them. It has nothing to do with them being more core (though they are) or how familiar we are with them. The simple fact is that the XPath data model on which canonicalization is based explicitly requires (section 5.2) that external entities be resolved and implicitly requires that XInclude elements not be resolved. The latter point is easiest to see in the context of XSLT. Consider this template rule: <xsl:template match="xinclude:include"> <p><xsl:value-of select="@href"/></p> </xsl:template> This template rule is completely unambiguous. XSLT defines exactly what is supposed to happen when this template matches an xinclude:include element. If you give me a document containing some xinclude:include elements, then I know how the processor is going to treat them. If a processor decides to do something else with the xinclude:include elements, then it is not conformant to XSLT. Of course you may also choose to give me a doucment which does not contain xinclude:include elements, in which case how XSLT/XPath handles it is equally unambiguous. Perhaps this document was generated from a document that did have XIncludes, perhaps it wasn't. Either way it is *not* the same document as one that does contain XIncludes. A lot of the confusion comes from wanting to treat xinclude:include elements as some magical thing that does not satisfy all the usual rules of XML processing, but that isn't true. An xinclude:include element is just like any other XML element which some processes may choose to impart certain semantics to. Most likely, these semantics will result in the production of a new and different document, but they don't have to; and in some cases they won't. -- +-----------------------+------------------------+-------------------+ | Elliotte Rusty Harold | elharo@m... | Writer/Programmer | +-----------------------+------------------------+-------------------+ | The XML Bible, 2nd Edition (Hungry Minds, 2001) | | http://www.cafeconleche.org/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.cafeconleche.org/ | +----------------------------------+---------------------------------+ 
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