RE: creation order vs. document order

>In all modesty I think that if I'm 
>having trouble understanding the formal semantics, then some other 
>people are probably also having a hard time getting their head around 
>it. That's actually one of the reasons why we are trying at the moment 
>to come up with a formal semantics for a small but relevant subset of 
>XQuery that can be used to do (database or other) theory.

The XQuery Formal Semantics Working Draft isn't introductory.  It assumes a
certain level of knowledge, which in my experience even most expert XML
developers/researchers lack.

I recommend you locate a copy of "XQuery from the Experts" (Katz et.al.;
Addison-Wesley, 2003; ISBN 0321180607), which has two introductory chapters
on the formal semantics and static typing.  I'd also recommend reading
papers on the nested relational algebra (NRA) and other efforts like TAX
(Tree Algebra for XML).  Personally, if I were creating a formal semantics
subset for XQuery for research and prototyping purposes, I would start with
the NRA.  (And in fact, that is where I started when inventing the
XSLT+XQuery+relational mapping algebra Microsoft uses in one of its
implementations.)

There's definitely a need for more introductory academic material on XML
algebras.  The relational calculus is older than I am and has a wide range
of reference material, but a formal semantics for XML is still in its
infancy and not yet widely understood (or even agreed upon).


-----Original Message-----
From: www-ql-request@w3.org [mailto:www-ql-request@w3.org] On Behalf Of Jan
Hidders
Sent: Wednesday, September 24, 2003 8:08 AM
To: www-ql@w3.org
Subject: Re: creation order vs. document order



Hello Mary,

Mary Fernandez wrote:
> 
> In the [XQuery 1.0 and XPath 2.0 Data Model], Section 4.3,
> there is a set of constraints on element nodes. #3 is
> the one that you are looking for:
> 
> "Element nodes must satisfy the following constraints.
> 
>      [....]
>         
>      3. The sequence of nodes in the children property is ordered and
>         must be in document order. ... etc..."

Indeed, that was exactly what I had overlooked and only realized afterwards.

> In the [XQuery 1.0 and XPath 2.0 Formal Semantics], Section 2.2 gives
> a formal notation for the XQuery Data Model, but it _does not_ repeat
> the constraints specified in the data model document.  The editors
> are working right now to make the relationship between documents
> more clear and to identify normative vs. informative text.  I will
> make a note to refer to the data model constraints explicitly in 
> Section 2.2.

That certainly would have helped. In all modesty I think that if I'm 
having trouble understanding the formal semantics, then some other 
people are probably also having a hard time getting their head around 
it. That's actually one of the reasons why we are trying at the moment 
to come up with a formal semantics for a small but relevant subset of 
XQuery that can be used to do (database or other) theory.

Having said that, I still think that the problem with the content 
construction for new elements *is* a real problem (although easy to fix) 
but I refer for that to my reaction to Peter's mail.

-- 
    Jan Hidders

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Received on Wednesday, 24 September 2003 13:08:36 UTC