W3C home > Mailing lists > Public > xproc-dev@w3.org > December 2008

Re: Calabash problem - primary port(s)

From: Norman Walsh <ndw@nwalsh.com>
Date: Sun, 07 Dec 2008 11:23:05 -0500
To: XProc Dev <xproc-dev@w3.org>
Message-ID: <m28wqsvtsm.fsf@nwalsh.com>
"Dave Pawson" <dave.pawson@gmail.com> writes:
> So, If I understand this...
>
> p:input wrapper
>    p:document tells it where to take input from
>
> p:output wrapper
>    p:document tells it where to get output from
>
> Which written like that seems daft IMHO.

Yes, inputs and outputs are asymmetrical. Whether that asymmetry is
daft or not, I'll leave for others to decide.

Consider the role of an atomic step in a pipeline. It accepts some
number of inputs and produces some number of outputs. It's a black
box. It doesn't make any sense for *the step* to control where its
output goes, that's the job for pipeline as a whole.

Now consider the role of a compound step. Like the atomic step, it's a
black box: it doesn't necessarily know what comes before it or after
it. (After all it may just be a declaration, it may not know
*anything* about the context in which it is used.)

What does the compound step have to know?

1. It has to know where its inputs come from.

2. It has to know what it should *write to its outputs*. Again, it
doesn't make any sense for the step to control where its output goes,
that's the job for the pipeline.


                                        Be seeing you,
                                          norm

-- 
Norman Walsh <ndw@nwalsh.com> | The Future Begins Tomorrow!--Yoyodyne
http://nwalsh.com/            | Propulsion Systems

Received on Sunday, 7 December 2008 16:23:45 GMT

This archive was generated by hypermail 2.2.0+W3C-0.50 : Sunday, 7 December 2008 16:23:46 GMT