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Document Order (was Re: The Scope of Step Names)

From: Alex Milowski <alex@milowski.org>
Date: Wed, 04 Oct 2006 09:48:35 -0700
Message-ID: <4523E5E3.8010000@milowski.org>
CC: public-xml-processing-model-wg@w3.org

Jeni Tennison wrote:
> Hi Alex,
> OK, I'm persuaded by your argument that if there's no technical reason 
> for components to be ordered then users should be able to order them in 
> whatever way makes sense to them. If they choose to use an order that 
> makes their pipeline hard to maintain or follow, that's up to them.
> However, given that we have no other way of indicating out-of-band 
> dependencies, I do think step order needs to be significant. If a user 
> writes
>  <p:step name="C" ...>
>    <p:input port="doc" step="A" source="result" />
>    <p:input port="aux" step="B" source="result" />
>  </p:step>
>  <p:step name="A" ...>...</p:step>
>  <p:step name="B" ...>...</p:step>
> and (implicitly) step A depends on step B, then the user will want step 
> A to be performed before step B.

Right now step ordering is done via input and output dependencies.  I
don't want to change that.

> In other words, the explicit dependencies between steps provide a 
> partial ordering; where the explicit dependencies do not specify an 
> ordering between two steps, the result must be as if the implementation 
> performed the steps in the order given in the pipeline specification.

I don't believe we can codify that because that relies on a explicit
definition of the graph structure.  We've decided to avoid explicitly
describing the graph and such a statement about document order makes
me very uncomfortable.

If there is an issue with explicit ordering and users need a way
to dictate that, I'd rather have an explicit "before" construct
in the language.

I think that many users just will not care because they are concerned
about the inputs and outputs.  In the case where they have side-effects
that they need to order, they'll need a better way than document
order in which to describe that constraint.

--Alex Milowski
Received on Wednesday, 4 October 2006 16:48:48 UTC

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