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Re: Serialization of XDM - Use cases / Proposal
- From: "David A. Lee" <dlee@calldei.com>
- To: Michael Kay <mike@saxonica.com>
- Date: Tue, 29 Sep 2009 10:31:45 -0400
Thanks Michael. In my mind, for this spec, ease of implementation
trumps borrowing from existing specs if you cant in fact reuse existing
technology.
e.g from what I can see
<xsl:sequence select="xs:positiveInteger('5')"/>
Has the advantage of borrowing from existing specs (xslt) but is
overweighted by the complexity of implementing the parser for say
"xs:positiveInteger('5')"
Not only would one have to write a parser for
<TYPE> '(' value ')'
(not too hard)
But because it is borrowing from existing specs the implication would
be that we'd have to parse *anything* that could otherwise be in
select="..."
That would require a full blown XPATH 2.0 parser.
Now of course we could refine the spec to limit the subset of XPATH 2.0
which is allowed to be in the select="" to only a small set of lexical
elements.
But then we're diverging from the original purpose of borrowing from
existing specs which is that they are familiar, we dont have to
re-document them, and they mean in this new spec fundamentally what
they meant in the spec were borrowing from.
Given that I'm going to suggest atomic values be
represented as a new element like
<atomicValue value="5" type="xs:positiveInteger"/>.
But try to reuse the other suggested XSLT elements for
documents, elements etc.
All in a new namespace .. (because they are not actually the same thing
as xsl: even if they are based on it).
I'm a bit on the fence if atomic values should have the value as an
attribute or body.
Attributes make sense for small values like the above, but what a very
common case of huge text.
<atomicValue value="This is a huge block of text
....
1000000 lines later" type="xs:string" />
Gives me the impression the value should be in the body.
<atomicValue type="xs:string">This is a huge block of text
....
1000000 lines later</atomicValue>
Could always support both variants :(
David A. Lee
dlee@calldei.com
http://www.calldei.com
http://www.xmlsh.org
812-482-5224
Michael Kay wrote:
A8BE77371C304F19BEF1624A7E68AB8C@Sealion"
type="cite">
The first question I have in mind is how do we parse this. This one
example of Michaels has me a little confused:
<xsl:sequence select="xs:positiveInteger('5')"/>
This is the proposal for how to represent a typed
atomic value. This is pretty obscure to my novice eyes. Reading
this I wouldn't guess off hand that this means "Atomic value, type
xs:positiveInteger, text value '5'".
Well, I think it's merit is that
it's familiar syntax and semantics for anyone who knows XSLT 2.0 or
wants to go and read the spec. For many purposes, however, a more
convenient syntax would be <atomicValue value="5"
type="xs:positiveInteger"/>.
That then leads me to the final question. Suppose we transform this
serialized form "almost an xslt" format, into "real xslt" format, then
run a real XSLT 2.0 parser on it. How to get the resulting values out ?
Please bear with me as I'm very much a novice at XSLT ... maybe the
answer is "obvious".
XSLT 2.0 claims that the result of an XSLT transformation can be a 'set
of result trees'.
Thats an XDM sequence . (???)
No: XQuery can produce any XDM
sequence as output (well, almost any - it can't for example generate
unparsed entities); but XSLT can only produce a set of document nodes.
You can write an xsl:function to produce any XDM sequence as its
result, but you would need a processor-specific way of invoking the
function and capturing its result in the external environment.
Incidentally, I was reminded of
this project in some work with a client yesterday. They are running
MarkLogic queries and feeding the result into Saxon, currently via
lexical XML (it has to be serialized because it's on a different
machine). In this kind of scenario it would be nice to transfer a typed
document, but we really don't want a five-fold increase in document
size over the lexical XML. Size does matter.
Regards,
Michael Kay
http://www.saxonica.com/
http://twitter.com/michaelhkay
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