Jonathan Robie jonathan at texcel.no
Tue Sep 1 17:36:37 BST 1998

At 11:19 AM 9/1/98 +0100, Michael Kay wrote:
>My immediate reaction is to compare this not with SQL, but
>with the new XSL "tree construction" facilities which
>essentially provide an XML transformation language. I don't
>have time to do a detailed point-by-point comparison but it
>would certainly be a useful exercise. Conceptually they have
>many similarities but there are many points of detail where
>one is stronger than the other. I would think it is entirely
>possible to devise a language that combines the power of
>both without a significant loss of usability.
In fact, at Metastructures 98 I presented a language called XQL that uses a
syntax very similar to XSL Patterns. This language was developed primarily
by Joe Lapp of webMethods and me. Like XML-QL, XQL is declarative.

One of the significant differences between XML-QL and XQL is that XQL can
do both hierarchy and sequence. The fundamental structural relationships in
XQL are:

o	hierarchy

	o	parent/child
	o	ancestor/descendant

o	sequence

	o	precedes
	o	immediately precedes

o	position

	o	subscripts
	o	ranges

I think sequence is pretty important in documents, though it is not
important in many data-oriented systems. XML-QL's heritage in relational
theory has caused it to ignore sequence.

jonathan at texcel.no
Texcel Research

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