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RE: [xml-dev] Serialization of XDM - Use cases / Proposal

From: Michael Kay <mike@saxonica.com>
Date: Mon, 21 Sep 2009 15:01:13 +0100
To: "'Michael Kay'" <mike@saxonica.com>, "'David A. Lee'" <dlee@calldei.com>
Cc: "'Philippe Poulard'" <philippe.poulard@sophia.inria.fr>, "'Kurt Cagle'" <kurt.cagle@gmail.com>, <rjelliffe@allette.com.au>, <xml-dev@lists.xml.org>, "'XProc Dev'" <xproc-dev@w3.org>
Message-ID: <0E8E215AA3DB430F863A2EB69888245B@Sealion>
Some people have been suggesting using a subset of XQuery syntax, others
have been saying it would be better to use XML syntax.
It occurs to me one might achieve both objectives at the same time by using
a subset of XSLT syntax. That is, we could define the syntax to be a named
xsl:template instruction containing a sequence constructor in which only the
following are permitted:
(a) An <xsl:sequence> instruction whose select attribute contains a
constructor function with a string literal argument, for example
<xsl:sequence select="xs:positiveInteger('5')"/>
(b) An empty <xsl:attribute>, <xsl:value-of>, <xsl:comment>,
<xsl:processing-instruction> or <xsl:namespace> instruction whose content is
constrained to use no non-literal expressions or AVTs.
(c) An <xsl:element> or <xsl:document> instruction whose content is
constrained to hold only <xsl:element>, <xsl:attribute>, <xsl:value-of>,
<xsl:comment>, <xsl:processing-instruction> or <xsl:namespace> instructions
that themselves follow the same rules.
There might be a need to define some additional attributes specific to the
serialization format, e.g. to represent IDness.

Michael Kay


From: Michael Kay [mailto:mike@saxonica.com] 
Sent: 21 September 2009 14:45
To: 'David A. Lee'
Cc: 'Philippe Poulard'; 'Kurt Cagle'; rjelliffe@allette.com.au;
xml-dev@lists.xml.org; 'XProc Dev'
Subject: RE: [xml-dev] Serialization of XDM - Use cases / Proposal


Ouch.  If this cant be done in xquery syntax then my goal of de-serializing
an XML representation using a XQuery example implementation is out the door.

Here's my best shot ... 

   { fn:QName( "U" , "P:N" ) } 
   { my:IdType( "S" ) }    (: wont work will it :( :)

Ok I admit I'm totally stumped.  *IS* there a way to re-animate this example
using XQuery (or XSLT?)  ?
I have a feeling that my goal of providing a reference implementation in
XQuery will be impossible.  Not even sure how to get element type
information re-animated.

I think that in XSLT, the following comes close:
<xsl:attribute name="P:N" namespace="U" type="my:IdType" select="'S'"/>
provided that the recipient has a schema (the correct schema) for the global
attribute declaration my:IdType. There are problems if the type is anonymous
(you might have to construct a variant of the original schema in which all
types have names). As for the isID property, it is ALMOST redundant in XDM:
it can in nearly all cases be inferred from the type annotation. The
exception is where IDness was established as a result of DTD validation
rather than schema validation. In that case, yes, I think you're going to
have difficulty reconstituting the original sequence using tools written in
XSLT or XQuery. (Actually, it hadn't occurred to me this was one of your
XQuery 1.0 (unlike XSLT 2.0) doesn't allow validation against a type name,
and doesn't allow validation of individual attributes. 
Other limitations of using XSLT/XQuery
(a) neither language gives you any way of creating unparsed entities
(b) XQuery 1.0 gives you no way of creating arbitrary namespace nodes

Michael Kay

Received on Monday, 21 September 2009 14:02:09 UTC

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