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Re: Determining whether a pipeline has a (defaulted) output

From: Norman Walsh <ndw@nwalsh.com>
Date: Wed, 07 Nov 2007 10:45:58 -0500
To: public-xml-processing-model-wg@w3.org
Message-ID: <m2ode63vpl.fsf@nwalsh.com>
/ Jeni Tennison <jeni@jenitennison.com> was heard to say:
| Alessandro Vernet wrote:
|> On 10/25/07, Henry S. Thompson <ht@inf.ed.ac.uk> wrote:
|>> [...]
|>> This achieves the stated goal, namely that the output defaulting rule
|>> can be applied w/o arbitrary recursion and analysis through named
|>> pipelines.
|> To reiterate on the argument I made during the call today, it looks to
|> me that this leads to a situation where to be valid, some pipelines
|> need to declare their outputs, while others do not. I think this will
|> create some confusion, as a pipeline author can't just look at the
|> outputs declared on the pipeline (maybe written by someone else) to
|> know what the outputs of that pipeline is.
| I agree with Alessandro. With this definition, I could define a
| pipeline library none of whose pipelines defined their inputs or
| outputs, and everything would work absolutely fine. I could even call
| pipelines from inside my other pipelines and never have a complaint.
| Until I happened to call one as the last step in a pipeline (perhaps
| because I just comment out the following code during debugging). Then
| suddenly I get an error not about the pipeline I'm currently working
| on, but about the one that it's calling not having defined its
| outputs. I think this will seem really arbitrary.


| On the other hand, I understand Henry's (and Richard's) urge to
| make/keep simple pipelines simple.
| So what about a rule that says "if a pipeline is called *at all* then
| it must have declared its inputs and outputs explicitly". This keeps
| the neat defaulting rules for the common/simple case of a single
| pipeline to do a quick job, but means that if you're planning to
| expose your pipelines for other people to call, then you have to take
| the extra step of declaring the inputs and outputs to the pipeline.

That seems reasonable to me.

                                        Be seeing you,

Norman Walsh <ndw@nwalsh.com> | If we lived alone in a featureless
http://nwalsh.com/            | desert we should learn to place the
                              | individual grains of sand in a moral or
                              | aesthetic hierarchy.--Michael Frayn

Received on Wednesday, 7 November 2007 15:46:11 UTC

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