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Re: Execution order of steps in a pipeline

From: Henry S. Thompson <ht@inf.ed.ac.uk>
Date: Wed, 23 Jan 2008 16:07:19 +0000
To: Toman_Vojtech@emc.com
Cc: <public-xml-processing-model-comments@w3.org>
Message-ID: <f5bodbcseyw.fsf@hildegard.inf.ed.ac.uk>

Hash: SHA1

Toman_Vojtech writes:

> "The result of evaluating a pipeline (or subpipeline) is the result of
> evaluating the steps that it contains, in an order consistent with the
> connections between them. [...]"
> I am sure this has been asked before (even though I could not find any
> discussion about this topic), but is this really necessary? Why cannot
> the execution of the contained steps just follow the document order?

How can you tell?  Are you hoping to depend on side-effects happening
in a particular order?  That would require not only that step
execution _began_ in document order, but that no step began execution
before all others 'before' it had finished.  I sure don't want to go
there, it rules out streaming.

I don't mind changing that sentence, but only if we make it _weaker_.

I persist in believing the spec. ought to support a simplistic
implementation which assigns a separate thread to every step, and
starts them all running, letting the sequencing of execution at all
levels depend entirely on availability of input (and of output
buffering).  I think it does so now.

- -- 
 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 Wednesday, 23 January 2008 16:07:35 UTC

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