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RE: [www-ql] <none>

From: Jonathan Robie <Jonathan.Robie@SoftwareAG-USA.com>
Date: Fri, 02 Mar 2001 12:27:58 -0500
Message-Id: <>
To: "Ingo Macherius" <macherius@darmstadt.gmd.de>, <www-ql@w3.org>
At 05:35 PM 3/2/2001 +0100, Ingo Macherius wrote:
> > I am not sure I understand what you mean by FLWR-XQuery. Do you mean
> > XQuery? There is only one language named XQuery, and FLWR is just one of
> > the ten or so expression types in XQuery.
>I can not agree there is just one language named XQuery, formerly known as
>"W3C XML Query". However, there is just one proposed syntax for it, yet,
>which I refer to as FLWR-XQuery. The other syntax will be at least
>XML-XQuery, while others like XSLT-XQuery or XPath-Xquery are worth while
>thinking of.

Let me quote from the XQuery specification:

<quote href="http://www.w3.org/TR/xquery">
XQuery is designed to meet the requirements identified by the W3C XML Query 
Working Group [Requirements]. It is designed to be a small, easily 
implementable language in which queries are concise and easily understood. 
It is also flexible enough to query a broad spectrum of XML information 
sources, including both databases and documents. The Query Working Group 
has identified a requirement for both a human-readable query syntax and an 
XML-based query syntax. XQuery is designed to meet the first of these 
requirements. An alternative, XML-based syntax for the XQuery semantics 
will be defined separately.

So according to my reading of the document, which the Working Group has 
approved, XQuery is the name of the syntax that is intended to be human 
readable. There is a BNF for it. There will be another, XML-based syntax.

>Thus I do not agree we can limit the term XQuery to a specific syntax

Well, let me take that as a suggestion from an outside party that the 
Working Group should have a name that covers both the XML syntax and the 
non-XML syntax. If you want to make sure we respond to that suggestion, you 
could send it to the comments list.

>I understand there currently can not be a literal roundtrip
>FLWR->Algebra->FLWR. But unless this becomes feasible, FLWR-XQuery must not
>be considered orthogonal enough. This may require some heuristics to
>disambiguate the rewrite to FLWR syntax.

Again, I do not really agree with you, but you should send this to the 
comments list if you want the group to respond.

Can you unpack this a little - what problems might arise if more than one 
XQuery expression can map onto the same XML Query Algebra expression?

> > into the XML
> > representation of the parse tree, the information content in the two
> > syntaxes is identical.
>As explained above, a true XML syntax will hopefully dissolve
>XPath-Expressions, FLWR-expression and and XSLT-ish RETURN sections into
>something which closely resembles Algebra expressions. I have to second
>Michael Rys here (even if I'm not so sure if he wasn't joking when writing
>his mail regarding this issue). For me this is what I expect from the XML
>syntax. Thus a roundtrip through the parse tree, or the XML syntax, should
>loose any syntactic dependencies from FLWR-Xquery. Just as relational
>algebra is independed of SQL syntax.

Clearly, we could have an XML representation of the Query Algebra in 
addition to our XML representation of XQuery. Where would you expect an XML 
representation of the XML Query Algebra to be used?

>Second, I think it's a bit vague to talk of "information content of
>syntaxes". We can only compare equality of query expressions on the
>operational semantic level, not in terms of parse trees similarities. This
>is what query optimization by equality and query rewrite for physical models
>is all about.

I don't think this is vague. What I mean is this: both XQuery and the XML 
representation should represent the abstract syntax found in Appendix B of 
the XQuery document.


These are my opinions right now. They may be quite different from the 
opinions of Software AG, the W3C XML Query Working Group, or the opinions 
that I will have after reading and considering your response.
Received on Friday, 2 March 2001 12:27:01 UTC

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