W3C home > Mailing lists > Public > public-xml-processing-model-wg@w3.org > January 2008

[closed] Re: A proposal to restructure our top-level syntax

From: Norman Walsh <ndw@nwalsh.com>
Date: Wed, 09 Jan 2008 12:58:19 -0500
To: public-xml-processing-model-wg@w3.org
Message-ID: <m2sl16yj7o.fsf@nwalsh.com>
We did it :-)

/ ht@inf.ed.ac.uk (Henry S. Thompson) was heard to say:
| Richard pointed out on yesterday's call that the type/name clash on
| p:pipeline arose, as have other issues, because of the schizophrenic
| nature of p:pipeline.  Bear with me, but that triggered a thought
| which I want to try to work through: we should use p:declare-step to
| declare all steps.  That is, not just spec-defined steps, and
| implementation-defined steps, but user-defined steps also.
| User-defined steps are the steps formerly known as named pipelines.
|
| Here's how this would look:
|
| 1) Add optional subpipeline content to p:declare-step -- if it's
|    present, it's the definition:
|
| <p:declare-step
|   type = QName>
|     (p:input |
|      p:output |
|      p:option)*
|      _subpipeline_
| </p:declare-step>
|
| 2) Simplify p:pipeline-library:
|
| <p:pipeline-library
|   ignore-prefixes? = prefix list
|   xpath-version? = string>
|     (p:import |
|      p:declare-step)*
| </p:pipeline-library>
|
| 3) Simplify p:pipeline itself -- it's now _only_ used for running
|    stuff, and is always nameless:
|
| <p:pipeline
|   ignore-prefixes? = prefix list
|   xpath-version? = string>
|     (p:input |
|      p:output |
|      p:option |
|      p:import |
|      p:declare-step |
|      p:log |
|      p:serialization)*,
|     subpipeline
| </p:pipeline>
|
| (Not sure why p:log is there -- can/should be removed?)
|
| 4) Remove the requirement that p:pipeline has to declare its inputs
|    and outputs -- applying the compound step output defaulting rule is
|    not a problem anymore, since all _named_ pipelines are defined with
|    declare-step, where i/o has never been defaulted.
|
| 5) Change the definition of p:pipe so that 'step' is optional, and if
|    omitted means the lexically inclosing p:pipeline.
|
| I think this is actually a much cleaner design.  It puts all the load
| of defining typed steps on declare-step.  It will actually make moving
| From user-defined to implementation-defined a very smooth transition
| -- we could even say that the content of a p:declare-step is actually
| a fallback -- implementations can supply builtin-definitions if they
| have them.
|
| I don't think Norm's other objection to my original 'require I/O decls
| only on libraries' proposal is as strong now -- to publish a pipeline,
| I just rename it to p:declare-step and wrap it in a
| p:pipeline-library, probably adding I/O declarations as well.  No
| internal changes are required.
|
| This also simplifies things in that p:import now _only_ imports
| libraries.  It will of course still be possible for an implementation
| to 'run' a library, defaulting to the first or only p:declare-step in
| the absence of a type argument.
|
| We get the defaulting of p:pipeline I/O back, because every step has
| mandatory I/O declarations, so there's no problem answering the "does
| the last step have a declaration?" question.
|
| Another way of looking at this is that p:pipeline is still special,
| it's just not a step anymore -- it's just a way of packaging a
| subpipeline so you can run it.
|
| I realise this will be a bit of a concept earthquake for those of us
| who have lived with the existing design for some time, but I think for
| new users it will appear perfectly natural.
|
| Here's what Ex 2 and the example pipeline library would now look like:
|
| <p:pipeline xmlns:p="http://www.w3.org/ns/xproc">
|   <p:input port="schemas" sequence="true"/>
|
|   <p:xinclude/>
|
|   <p:validate-with-xml-schema>
|     <p:input port="schema">
|       <p:pipe port="schemas"/>
|     </p:input>
|   </p:validate-with-xml-schema>
|
| </p:pipeline>
|
| <p:pipeline-library xmlns:p="http://www.w3.org/ns/xproc"
|                     xmlns:my="http://example.com/ns/pipelines">
|
| <p:import href="ancillary-library.xml"/>
| <p:import href="other-pipeline.xml"/>
|
| <p:declare-step type="my:validate">
|   <!-- validate declarations and subpipeline -->
| </p:declare-step>
|
| <p:declare-step type="myv:format"
|             xmlns:myv="http://example.com/vanity/mine">
|   <!-- format declarations and subpipeline -->
| </p:declare-step>
|
| </p:declare-step-library>
|
| One final note -- (1) above arguably oversimplifies, and so makes my
| assertion about how you publish a pipeline false, because as written
| it doesn't allow some things that p:pipeline does in its content.  I
| think on balance I'd prefer to be catholic about that, and so we should
| rather have
|
| <p:declare-step
|   type = QName>
|     (p:input |
|      p:output |
|      p:import |
|      p:declare-step |
|      p:serialization |
|      p:option)*
|      _subpipeline_
| </p:declare-step>
|
| with the stipulation that a) nested declarations and imports are _not_
| visible higher up; b) serialization is only relevant if the step is
| 'run'.  Which points out another collateral benefit -- p:serialization
| really belongs on p:declare-step, because its perfectly coherent to
| ask an implementation to 'run' a step from a pipeline library w/o
| knowing or caring whether it's declared built-in or user-defined,
| that is, without or with an explicit subpipeline.
|
| Thanks for listening :-)
|
| ht
| --
|  Henry S. Thompson, HCRC Language Technology Group, University of Edinburgh
|                      Half-time member of W3C Team
|     2 Buccleuch Place, Edinburgh EH8 9LW, SCOTLAND -- (44) 131 650-4440
|             Fax: (44) 131 650-4587, e-mail: ht@inf.ed.ac.uk
|                    URL: http://www.ltg.ed.ac.uk/~ht/
| [mail really from me _always_ has this .sig -- mail without it is forged spam]

                                        Be seeing you,
                                          norm

-- 
Norman Walsh <ndw@nwalsh.com> | The art of living is more like
http://nwalsh.com/            | wrestling than dancing.--Marcus Aurelius

Received on Wednesday, 9 January 2008 17:54:45 GMT

This archive was generated by hypermail 2.2.0+W3C-0.50 : Wednesday, 9 January 2008 17:54:45 GMT