RE: multiple sorting

Yuko Caras writes:
>Woops. Is there a problem using Xalan?  They [Jeni Tennison's
>sorting techniques] work well with saxon and xt
>but having a trouble with Xalan...

Could you be specific, and say which version of Xalan? I think
that the techniques as she presented them would work in the
latest version. One involves a union, and we had a little
trouble with unions in a recent version, but not in 1.2D01.

I'd also suggest a caution in setting up "futile" sorts,
which is a key part of the suggested techniques. The XSLT
spec is clear about how to deal with data that exists but
compares equal, but the case where the sort key doesn't
exist is shrouded in indirection. I think that the verbiage
about how the sort key is evaluated covers the techniques
presented here, but it gets right to the borderline. If the
sort key is something that can't be evaluated, then the
processor could decide not to sort and presumably raise
an error. If the processor instead presented the nodes in
their original document order, I can't find anything in
the spec to prohibit it.

There is an additional question about where null values
(like NaN in numeric sorting) are placed. One of the
techniques has nested sorts, which would be affected by
this behavior.
.................David Marston


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