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Re: question about xlink 1.1

From: Henry S. Thompson <ht@inf.ed.ac.uk>
Date: Tue, 16 Jun 2009 14:54:12 +0100
To: "Grosso, Paul" <pgrosso@ptc.com>
Cc: <public-xml-core-wg@w3.org>
Message-ID: <f5br5xkp9mj.fsf@hildegard.inf.ed.ac.uk>
Hash: SHA1

Grosso, Paul writes:

> HST writes
>> Who raised this point, anyway?
> I see it mentioned in our minutes first last July at
> http://lists.w3.org/Archives/Public/public-xml-core-wg/2008Jul/0012
> in minutes taken by Norm with Henry, Daniel, and Glenn in attendance.
> I believe it is in response to the email thread at
> http://lists.w3.org/Archives/Public/public-xml-core-wg/2008Jul/0005.html
> which was started by you, Henry.

Heh.  My earlier self was more thoughtful/careful/pernickety than the
currently avaliable version, it seems :-)

OK, the DTD is right, and makes a careful distinction, which the XSD
schema does as well:


 <!ENTITY % simpleAttrs
     'xlink:type      (simple)        "simple"
      . . .
 <!ENTITY % extendedAttrs
     'xlink:type      (extended)      #FIXED "extended"


 <xs:attributeGroup name="simpleAttrs">
  <xs:attribute ref="xlink:type" fixed="simple"/>
 <xs:attributeGroup name="extendedAttrs">
  <xs:attribute ref="xlink:type" fixed="extended" use="required"/>
In XML Schema, "fixed='[some value]'" means "Has this value in the
PSVI -- if present in the input, must match"  and, orthogonally,
"user='required'" means "must be present in the input".

However, I am left with one residual query in this area:  why isn't
href #REQUIRED in simpleAttrs in the DTD (and schemas)?  Why does the
spec. say "it MAY be used on simple-type elements"?  What does a
simple link w/o an href mean?


Oops, I also note that in section 5.3 of the text [1] we find

  <!ATTLIST simple-link-element
     xlink:type      (simple)        #FIXED "simple"

which is not as good, in my view, as what's in the DTD:

 <!ENTITY % simpleAttrs
     'xlink:type      (simple)        "simple"

I have to say on re-reading this, I find all the schema examples more
intrusive than helpful, particularly the lengthy and to me
incomprehensible "Sample simple-Type Element Declarations and
Instance" in section 5.2 [2].

The schemas are all there in appendices, isn't that sufficient?


[1] http://www.w3.org/TR/2008/WD-xlink11-20080331/#link-types
[2] http://www.w3.org/TR/2008/WD-xlink11-20080331/#simple-links
- -- 
       Henry S. Thompson, School of Informatics, University of Edinburgh
                         Half-time member of W3C Team
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                Fax: (44) 131 651-1426, e-mail: ht@inf.ed.ac.uk
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Received on Tuesday, 16 June 2009 13:54:47 UTC

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