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Re: An XML API using Java streams

  • From: Hans-Juergen Rennau <hrennau@yahoo.de>
  • To: Michael Kay <mike@saxonica.com>
  • Date: Fri, 23 Jun 2017 10:41:19 +0000 (UTC)

Re:  An XML API using Java streams
As the expressiveness of XPath is excellent (and I think - not to be surpassed), any fresh attempt at a navigation model might profit from a comparison of its key principles with the key principles behind XPath. I would summarize the latter as follows:

(1) Navigation is a sequence of steps.
(2) A step is a mapping of current locations to next loations.
(3) A step is either a standard step or a custom step.
(4) A standard step has a direction (axis) and a simple standardized filter (node name or kind).
(5) A step can be extended by custom filters.
(6) The addition of step filters does not increase the complexity of the navigation.
(7) Step semantics are self-contained and any step can be applied to any input

Michael Kay <mike@saxonica.com> schrieb am 16:00 Donnerstag, 22.Juni 2017:

(2) A great challenge - and perhaps a hopeless one - would be to create an expressiveness which could at least be a far cry of what XPath offers. It is strange to say
when what you really want to say is

Excellent point. However, dropping into another language does have all sorts of disadvantages: apart from the learning issues, there's the lack of compile-time syntax checking and type checking, the cost of dynamic compilation/interpretation, etc.

One thing to look at, perhaps, is how it translates into Scala, where you can define your own operators:

A.flatMap(B)   -->   A/B

A.attribute(B)  -->   A @ B

etc; and then we start to have something very XPath-like, but with a syntax that's compiled and validated by the host language.

Michael Kay

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