[xquery-talk] RE: aggregate , grouping

David Carlisle davidc at nag.co.uk
Thu Dec 22 22:23:48 PST 2005

> 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.


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