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[XML-DEV Mailing List Archive Home] [By Thread] [By Date] [Recent Entries] [Reply To This Message] Re: Possible schema validation issue in 3.0b3
"Falk, Alexander" wrote:
>
> This message is a question concerning the use of entities to emulate
> namespace prefixes in a DTD - a technique that is being used by the
> normative DTD from the April 7 XML Schema draft.
Hmm... I thought the DTD was informative...
making it normative seems to conflict with the use
of anyAttributes...
"<complexType name="openAttrs" content="empty">
<annotation>
<documentation>This type is extended by almost all schema
types
to allow attributes from other namespaces to
be
added to user schemas.</documentation>
</annotation>
<anyAttribute namespace="##other"/>
</complexType>
"
-- http://www.w3.org/TR/2000/WD-xmlschema-2-20000407/#schema
but there it is:
"B (normative) DTD for Schemas"
http://www.w3.org/TR/2000/WD-xmlschema-1-20000407/#normative-schemaDTD
I don't see any prose that actually says "an XML schema must
match the DTD in appendix B", though. Odd.
> I'm therefore intentionally
> posting this to both xml-dev and xmlschema-dev, as it is relevant to both
> discussion forums:
>
> Recently one of our customers has reported an entity-resolution tech-support
> issue in our "XML Spy" product ( http://www.xmlspy.com ), that has resulted
> in a very interesting internal discussion regarding the addition of leading
> and trailing spaces in the resulution of parameter entities (section 4.4.8
> of the XML 1.0 specification - see http://www.w3.org/TR/REC-xml#as-PE ).
>
> The problem is this - section 4.4.8 explicitely says:
>
> When a parameter-entity reference is recognized in the DTD and
> included, its replacement text is enlarged by the attachment of
> one leading and one following space (#x20) character; the intent
> is to constrain the replacement text of parameter entities to
> contain an integral number of grammatical tokens in the DTD.
>
> This section has also never been corrected by any errata (to the best of our
> knowledge) and the annotated XML specs also don't mention a word about it
> other than pointing at the SGML history issues.
And yet none of the software I'm aware of follows this part of the
spec. I'm copying xml-editor, since this is clearly a discrepancy
between the XML 1.0 spec and implementations.
> Now we've already seen many DTDs - and interestingly the normative XML
> Schema DTD from the April 7 draft (see
> http://www.w3.org/TR/xmlschema-1/#normative-schemaDTD ) is one of them -
> that uses parameter entities to make DTDs pseudo-namespace-aware.
>
> The trick most commonly used is to define a prefix and suffix entity that
> can then be overridden in the internal subset of any document using this DTD
> - and then use this prefix in defining any other element via another entity.
> Here is an example from the normative XML Schema DTD:
>
> <!ENTITY % p ''>
> <!ENTITY % s ''> <!-- if %p is defined (e.g. as foo:) then you must
> also define %s as the suffix for the appropriate
> namespace declaration (e.g. :foo) -->
> <!ENTITY % nds 'xmlns%s;'>
>
> <!-- Define all the element names, with optional prefix -->
> <!ENTITY % schema "%p;schema">
> <!ENTITY % complexType "%p;complexType">
> <!ENTITY % element "%p;element">
> <!ENTITY % unique "%p;unique">
> ...
>
> So by defining %p as 'xsd:' and %s as ':xsd' you can actually validate any
> XML Schema that uses xmlns:xsd to refer to the XML Schema namespace using
> this DTD, because this will result in all Schema elements being defined as
> xsd:schema, xsd:complexType, xsd:element, etc.
>
> Or so it seems. But this is where section 4.4.8 actually comes into play! If
> the XML Schema DTD defines an entity %schema using
>
> <!ENTITY % schema "%p;schema">
>
> and we assume %p has already been defined as 'xsd:' then section 4.4.8 tells
> us that %schema will actually be defined as " xsd: schema", which is
> certainly not a valid qualified name and the behavior intended by the
> authors of the normative DTD.
>
> So the real question is: is this use of pseudo-namespace prefixes in a DTD
> really XML 1.0 compatible?
It seems to be compatible with lots of tools but not witht the XML 1.0
spec as written. Ouch.
> And how should XML toolmakers interpret section
> 4.4.8 in the light of such use in new W3C drafts?
I'm afraid I don't have a ready answer.
>
> Sincerely,
>
> Alexander Falk
>
> P.S. Last time we had a tricky XML specification question, my colleague
> wrote "please answer only, if you are absolutely sure" - and we received
> only one answer from Tim Bray, which was right to the point. So I wonder, if
> I shouldn't also be adding such a restriction this time ;)
>
> ... Icon Information-Systems
> ... ALEXANDER FALK
> ... President, CEO
> ... http://www.icon-is.com/falk
>
> =========================================================================
> XML Spy 3.0 - the first true Integrated Development Environment for XML
> Visit http://www.xmlspy.com/ to download a free 30-day evaluation version
> To get a demonstration, come see us at XML DevCon in New York, June 26+27
> If you like our product, please vote for us at http://www.xmlspy.com/vote
> =========================================================================
--
Dan Connolly, W3C http://www.w3.org/People/Connolly/
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