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Re: Inputs and outputs

From: Alessandro Vernet <avernet@orbeon.com>
Date: Wed, 15 Mar 2006 19:05:26 -0800
Message-ID: <4828ceec0603151905h7ee34311x222e478c1d3aa93b@mail.gmail.com>
To: public-xml-processing-model-wg@w3.org

On 3/15/06, Norman Walsh <Norman.Walsh@sun.com> wrote:
> A few design notes and sketches. (Syntax imaginary)
> [...]

Hi Norm,

For having written a number of pipelines during the last few years in
XPL, I realize that even if the language allows for arbitrary
connections between steps, it is fairly frequent to have steps that
are just connected in sequence. In that case, having to declare an
output just to reference it a few lines below can seem like a lot of
work, and so I am enticed by your proposal to consider implicit
input/outputs.

Taking into consideration the method you are suggesting, I am trying
to think about what the implications of implicit <p:input> and
<p:output> are on pipelines using steps that do not take any input, or
similarly do not generate any output document. Consider this pipeline:

    <p:step name="xinclude">
        <p:input href="somedocument.xml"/>
    </p:step>

    <p:step name="url-serializer">
        <p:param name="url">file:///somefile.xml</p:param>
    </p:step>

    <p:step name="user-credentials">
        <p:output name="credentials" label="..."/>
    </p:step>

    ... pipeline continues ...

Here the first and second steps are implicitly connected: the
"xinclude" step generates a document used by the "url-serializer"
step. The second and third steps are not implicitly connected: I
assume that the "url-serializer" step does not generate any document,
and "user-credentials" step does not take any document in input. It
bothers me that those two cases would look exactly the same in our
pipeline language, and that one has to know about the interface of
each step to see when steps are connected, and to even know if the
steps in the pipeline are correctly connected with each other.

> [...] I'm not sure I like the idea of making any of
> the inputs and outputs implicit; it seems like it might lead to
> confusion.

Because of this and other considerations related to the downsides of
making things implicit in general, I am also gearing towards thinking
that having implicit inputs/outputs is not a good idea.

Alex
--
Blog (XML, Web apps, Open Source):
http://www.orbeon.com/blog/
Received on Thursday, 16 March 2006 03:50:29 GMT

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