[xquery-talk] RE: aggregate , grouping

[Michael Rys]

I think one of the problems with the additional axes (and the parent
axis) are that the static typing rules are much more complex and would
have taken more time to get usable. To declare these axes as optional
allowed the spec writers to postpone the work to get the static-typing
right. The parent axis was deemed more important however, so the static
typing there is also not very usable but the axis is in...

I would assume that implementations will add support for it when users
really request it. And at some point a future version of the XQuery
standard may decide to move the functionality into the core...

Best regards
Michael



> -----Original Message-----
> From: David Carlisle [mailto:davidc at nag.co.uk]
> Sent: Thursday, December 22, 2005 2:24 PM
> To: Michael Rys
> Cc: talk at xquery.com
> Subject: Re: [xquery-talk] RE: aggregate , grouping
> 
> 
> > Unfortunately, SQL Server currently does not offer the full axis
> > feature.
> 
> It's not surprising (and not unreasonable) if at the current stage of
> the game some (or even most) Xquery implementations don't implement
the
> full spec, or implement earlier drafts, or whatever. That would be the
> case whether or not a feature is declared optional. I suppose the
> question I should have asked is are there any implementations that
don't
> intend _ever_ to implement all the axes. If not, why are they
optional?
> As Michael Kay says, it inflicts pain on authors of portable xquery
code,
> forever, apparently just to give implementors some transient benefit
of
> claiming full conformance to a slightly smaller spec.
> 
> It would be more understandable if not implementing the full axs
feature
> restricted to some set of xpath expressions with restricted
> functionality that always looked "forwards" and so perhaps helps some
> streaming implementations. But as it is, the choice of optional axes
just
> seems arbitrary, you still have parent:: and root() and << so not
having
> the full set of axes doesn't remove any functionality, it just
inflicts
> on the end user the requirement to make an inconvenient syntactic
> rewrite to remove the dropped axes.
> 
> David
> 
>
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