xproc api

[xquery]

cnp'ed from email from @htInEdin

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I understood someone (who?) to say something along the lines of: "I'd
like an API I could use to get a pipeline built".

That happens to fit pretty well with the way I've been trying to address
the 'abstract semantics' problem. And at lunch today, where I ended up
with Mohamed, Romain, Florent and John Snelson, we had a useful
discussion about possible language architectures, i.e. how many
languages do we have, and what's their relationship.

We came up with at least the following possibilities:

1. The XML syntax defines the language, there is a read-only textual
   version;

2. The XML syntax defines the language, there is an executable textual
   syntax, but it's not normative nor is support required for
   conformance (this was asserted to be the RNG/RNC story);

3. The compact syntax is normative, it maps to an XML language which
   defines the semantics but is not optimised for human-readability
   (this could be sort of Vnext as we had been working towards it,
   perhaps w/o (much) defaulting);

4. The compact syntax is normative, it maps to a set of logical
   assertions/object creation calls which defines the semantics, and
   which in turn has an XML syntax (what I think I heard from the
   floor).

Wrt the very preliminary way I've been going about this, here's what (4)
would look like for a trivial example:

s1 == StepImpl(p:load,uri="somedoc.xml")
s2 == StepImpl(p:data,type="application/xml",data="")
s3 == StepImpl(p:set-attributes,match="//*[@colour='red']")
s4 == StepImpl(p:serialize)
p1 == Pipe(s1.result,s3.source)
p2 == Pipe(s2.result,s3.attributes)
p3 == Pipe(s3.result,s4.source)

The XML for this is left as an exercise for the reader.

[ndw]

[I think we need to define a model for what is represented by the pipeline language and processing model for what it means to "run" a pipeline. I'm not convinced it has to map onto a single, explicit programming language API. I think the text syntax should be the normative representation of the model. I think we should provide a complete XML syntax that's suitable for manipulating with an XML toolchain.

I think that syntax should be more like XProc 1.0 (perhaps with a different story for connections and less defaulting) and less like XQueryX, but I could be wrong about that.

[mgaerber]

I would find it most usable to also have an API that is pure XQuery 3.x. Either as an intermediate representation or the new syntax itself.

I am sure that there will be several more implementations of the standard as soon as XQuery engines could provide it as a module.