Re: Execution order of steps in a pipeline

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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.

ht
- -- 
 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
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                   URL: http://www.ltg.ed.ac.uk/~ht/
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Received on Wednesday, 23 January 2008 16:07:35 UTC