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Re: Execution order of steps in a pipeline

From: Henry S. Thompson <ht@inf.ed.ac.uk>
Date: Thu, 24 Jan 2008 17:26:29 +0000
To: Toman_Vojtech@emc.com
Cc: <public-xml-processing-model-comments@w3.org>
Message-ID: <f5bsl0nw2wq.fsf@hildegard.inf.ed.ac.uk>

Hash: SHA1

Toman_Vojtech writes:

> What I wanted to say is that no matter in which implementation-specific
> order the steps are executed, the end result of a pipeline should be the
> same as running the steps sequentially, in document order.

I still don't understand what "running the steps sequentially" means.
Does it mean starting them?  If so, the spec. already guarantees what
you want, because it's a subcase of what I want, i.e. that starting
the steps in _any_ order gives the right result.

> I think the XProc processor can still run the identity steps in parallel
> if it can detect that there is no dependenty between them.

For sure.

> But the specification also allows "forward" bindings to steps that
> follow in document order:

The Working Group discussed this at length, and we don't think
removing that flexibility is in the general interest.  People should
be free to write their pipelines in whatever order helps _them_
understand them best.

> <p:pipeline>
>   <p:identity name="id1">
>     <p:input port="source">
>       <p:pipe step="id2" port="result"/>
>     </p:input>
>   <p:identity name="id2"/>
> </p:pipeline>
> Which is something I sort of don't like because I find it confusing and
> not natural. But again, maybe there are use cases where we may need this
> - and from that perspective, it makes sense to be prepared for it...
> It's just that I like the simple, linear nature of pipelines much more.

No problem.  You may always write your pipelines that way.  The
spec. already guarantees that the result may not vary on the basis of
what order you write the steps.

But we don't agree that anyone should be _forced_ to write in that
way, sorry.

- -- 
 Henry S. Thompson, HCRC Language Technology Group, University of Edinburgh
                     Half-time member of W3C Team
    2 Buccleuch Place, Edinburgh EH8 9LW, SCOTLAND -- (44) 131 650-4440
            Fax: (44) 131 650-4587, e-mail: ht@inf.ed.ac.uk
                   URL: http://www.ltg.ed.ac.uk/~ht/
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Received on Thursday, 24 January 2008 17:26:56 UTC

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