xsl query or transformation language
paul at arbortext.com
Tue Sep 1 20:05:30 BST 1998
At 17:28 1998 09 01 +0100, Henry S. Thompson wrote:
>Lisa Rein <lisarein at finetuning.com> writes:
>> Henry I am a little confused about perceiving XSL as a query language.
>> It was my understanding that it aims to be a transformation language,
>> like DSSSL, that works with a query or scripting language to
>> transform/process and format data.
>Well, XSL defines its own query syntax for walking the input document
>a) for the purposes of deciding which style rules to apply to
>which input document components (in which case you should think of a
>query as returning a 'yes this matches' or a 'no this doesn't match'
>result when applied to a node in the tree;
Since what gets said here might get copied elsewhere, we should be
careful about wording.
XSL currently has no style rules and may never. Henry is referring
to construction rules here.
I would disagree with Henry that pattern matching is querying in any
useful, usual sense of the word. If there is a "query" (in the
non-technical sense of the word) at all here, it's "given a node in
the source document tree, what construction rule's pattern best matches
the given node's context?" I don't see this as "returning" anything
in the usual sense, and I don't think it's helpful to confuse this
with what most people think of as queries even if the syntax of
match patterns is similar to (or even the same as) the syntax of
select patterns (which is what Henry discusses below).
I also disagree that XSL "walks the tree" as Henry mentions above.
I agree that the syntax of XSL patterns (both match patterns and
select patterns, since they use almost the same syntax) is a potentially
useful syntax for an XML-aware query language.
>b) for the purposes of finding one or more bits of the tree to process
>next, given a starting point (the node we're processing now), in which
>case you should think of a query as returning a set of nodes in the
>tree given a starting point.
>A variant of type (b) where you just want the first element of the set
>occurs as well.
>Sounds like what I mean by a query language, how about you?
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