W3C home > Mailing lists > Public > xproc-dev@w3.org > June 2009

Re: Implicit output ports and p:declare-step

From: Henry S. Thompson <ht@inf.ed.ac.uk>
Date: Wed, 24 Jun 2009 16:51:54 +0100
To: <Toman_Vojtech@emc.com>
Cc: <xproc-dev@w3.org>
Message-ID: <f5bab3x7hph.fsf@hildegard.inf.ed.ac.uk>
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[anon] writes:

> I feel the same. I lean towards saying that this does not apply to
> p:declare-step, exactly because it is "an interface to the outside
> world". And you don't really want to have pipelines having unnamed
> implicit output ports, IMHO. ...althought at times, especially when you
> want to be lazy and save some typing, thay may be convenient. 

When I use declare-step with a name and an explicit subpipeline,
e.g. in a library, I certainly expect it to behave like any other
compound step, I think. . .

Hmm, the spec says the following:

  If a primary output port is declared and that port has no binding,
  then it is bound to the primary output port of the last step in the
  subpipeline. It is a static error (err:XS0006) if the primary output
  port has no binding and the last step in the subpipeline does not
  have a primary output port.

So this doesn't say anything at all about what happens if no POP is
declared, although the static error discussion would appear to apply
in that case as well?

> Personally, I think that p:declare-step should behave the same for both
> atomic and compound steps. Saying that in the case of compound steps you
> may get some magical output ports smells to me. I prefer steps with an
> obvious signature.

Hmm, it makes sense to me.  We really have two distinct
functionalities:
  1) define step (implementation explicit);
  2) declare step signature (implementation unspecified)
for which we use the same tag.  I think it makes sense that the
defaulting rules go with the function, and so are different.

I still don't see the downside wrt case (1) when we go even further
and mean "and run it", i.e. when the declare-step is the entire
content of a pipeline document.

ht
- -- 
       Henry S. Thompson, School of Informatics, University of Edinburgh
                         Half-time member of W3C Team
      10 Crichton Street, Edinburgh EH8 9AB, SCOTLAND -- (44) 131 650-4440
                Fax: (44) 131 651-1426, e-mail: ht@inf.ed.ac.uk
                       URL: http://www.ltg.ed.ac.uk/~ht/
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Received on Wednesday, 24 June 2009 15:52:35 GMT

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