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Re: The Scope of Step Names

From: Jeni Tennison <jeni@jenitennison.com>
Date: Wed, 04 Oct 2006 15:23:58 +0100
Message-ID: <4523C3FE.2060806@jenitennison.com>
To: public-xml-processing-model-wg@w3.org

Hi Alex,

Alex Milowski wrote:
> Norman Walsh wrote:
>> / Alex Milowski <alex@milowski.org> was heard to say:
>> | Erik Bruchez wrote:
>> |>
>> |> Alex Milowski wrote:
>> |>
>> |>  > 1. Step must be able to refer to other steps that are
>> |>  >    siblings (preceding and following) otherwise you
>> |>  >    can't connected steps at all.
>> |>
>> |> "Preceding siblings" would be enough IMO.
>> |
>> | I don't think we want to limit to preceding siblings.  If a user
>> | wants to structure their pipeline "logically" from their perspective,
>> | such a limitation would get in the way.  I can't see how it is
>> | any issue for an implementer.
>> |
>> | Similarly, if a user can't easily determine "before" or just wants
>> | to quickly insert a step into their pipeline, they shouldn't have
>> | to figure out what "preceding sibling" means just to do that.
>>
>> If we imagine that many (perhaps most) authors will eventually rely
>> on defaulting at least sometimes, the order of steps will be very
>> important. I don't see any benefit in saying that sometimes it isn't.
>> And "before" is pretty easy to determine.
> 
> I absolute do not thing "before" is easy in all instances.  In addition,
> considering we have no defaulting story, I don't a "yet-to-be determined
> defaulting story" should be involved in making this decision.

Do you have an example of a situation where "before" is not easy (for a 
user) to define?

I agree with Erik and Norm that references should only be allowed to 
preceding siblings (and children of a container).

First, I don't follow your argument that users will not want to have to 
locate the place for a step to be inserted. They will have to locate 
that point in order to change the <p:input> of the next step. For 
example, if they start with:

  <p:step name="foo" ...>
    <p:input port="doc" ...>
  </p:step>

  <p:step name="bar" ...>
    <p:input port="doc" step="foo" source="result" />
  </p:step>

and they want to insert a step called 'baz' in between the 'foo' and 
'bar' steps, they have to locate the 'bar' step to change the <p:input>. 
Having located that point, scrolling up two lines in order to insert the 
step does not seem particularly burdensome.

Second, I agree that it implementations will have no problems 
understanding the flow, whatever the order of the steps. But I also 
agree with Erik that *users* will have a *huge* problem understanding 
the flow of a pipeline if the components aren't specified in the order 
that they should execute.

Finally, all signs at the moment indicate that we're going to end up 
with a situation where components can be non-functional and have 
side-effects. That being the case, the only way we can get any kind of 
consistent behaviour between implementations is to say something like

   The result of executing a pipeline must be as if each
   component were executed once, in the order specified.

So I think the order of components in the document is very important 
even without a defaulting story.

Cheers,

Jeni
-- 
Jeni Tennison
http://www.jenitennison.com
Received on Wednesday, 4 October 2006 14:24:10 GMT

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