RE: aggregate , grouping

[Michael Kay]

> I don't know of an implementation that doesn't provide a full axis
> feature. However, with some internal data layouts (some numbering
> schemes for splitting trees into tables actually) it can be really
> difficult to provide those axis in a efficient fashion, so that's
> probably why.
> 

Yes, I regret to say that the XQuery WG has sometimes made such decisions in
the interests of implementors rather than users.

The problem is of course that because the feature is optional, users who
want to write portable code are obliged to use workarounds which are likely
to be inefficient on *all* implementations.

Michael Kay
http://www.saxonica.com/