- From: Norman Walsh <Norman.Walsh@Sun.COM>
- Date: Tue, 28 Mar 2006 14:42:12 -0500
- To: public-xml-processing-model-wg@w3.org
- Message-ID: <874q1iz78r.fsf@nwalsh.com>
See also: http://www.w3.org/XML/XProc/2006/03/23-minutes.html
(Apologies for tardiness.)
W3C[1]
- DRAFT -
XML Processing Model WG
23 Mar 2006
Agenda[2]
See also: IRC log[3]
Attendees
Present
Andrew, Paul, Rui, Alex, Henry, Richard, Alessandro, Norman,
Murray, Michael
Regrets
Erik
Chair
Norm
Scribe
Norm
Contents
* Topics
1. Administriva
2. Accept this agenda
3. Accept minutes of 9 Mar?
4. Accept minutes of 16 Mar?
5. Next meeting 30 Mar
6. Technical
7. Conditionals and sub-pipelines
8. Sub-pipelines
9. Any other business
10. Face-to-face in August in Toronto
* Summary of Action Items
----------------------------------------------------------------------
Administriva
Accept this agenda
Accepted
Accept minutes of 9 Mar?
Accepted
Accept minutes of 16 Mar?
Accepted
Next meeting 30 Mar
Regrets from Henry
Technical
<scribe> ScribeNick: MSM
AM: have made a number of formatting and stylistic changes.
... Table is compacted, I hope it's easier to read.
... The use cases now have identifiers which can remain constant across
reorderings.
NDW: I'm comfortable with publishing this, although I still have questions
about the table.
AM: well, the table should be either completed or dropped. it's valuable,
but it's not worth delaying publication over.
NDW: recall that the use cases and requirements are not fixed and
immutable from this point on.
<PGrosso> http://www.w3.org/XML/XProc/2006/03/23-agenda.html[4]
MM: let's make it invisible rather than deleting it.
<PGrosso> http://www.w3.org/XML/XProc/docs/langreq.html#use-cases[5]
clarification: it's the table at the beginning of sec 5 we are talking
about
<Norm> ScribeNick: Norm
MSM: I'd rather leave the table in place with a note to say that it's
incomplete
Murray: Is that an offer to complete it?
<scribe> ACTION: MSM to draft a complete table; ETA: 21 Apr 2006 [recorded
in http://www.w3.org/2006/03/23-xproc-minutes.html#action01[6]]
We'll publish the document with the table, with a note that it's
incomplete
<scribe> ACTION: Alex: add a note to the effect that the table is
incomplete [recorded in
http://www.w3.org/2006/03/23-xproc-minutes.html#action02[7]]
Proposal: The WG has consensus to publish the Use Cases and Requirements
document with minor editorial changes including a reordering of the Use
Cases.
Accepted
<scribe> ACTION: Norm to request first-public-working draft status
[recorded in http://www.w3.org/2006/03/23-xproc-minutes.html#action03[8]]
Publication date: 4 Apr 2006
<scribe> ACTION: Alex to produce a draft with reordered use cases by 29
Mar 2006 [recorded in
http://www.w3.org/2006/03/23-xproc-minutes.html#action04[9]]
Conditionals and sub-pipelines
<richard> http://www.cogsci.ed.ac.uk/~richard/pipeline.html[10]
Norm observes that last week Henry tried to outline Richard's position.
Norm asks Richard if he has anything to add
Richard: On reflection, the work we did at the face-to-face was too
complex.
... Having components with unread inputs or unwritten outputs spreads the
conditional across the whole pipeline
... I'm not suggesting a simpler approach where the
inputs/outputs/parameters of each side of the branch must be the same
... I'm still suggesting that the test be controlled by an XPath over a
separate documents
... What if you want the two branches to have different inputs?
... You can put the inputs inside the conditionals.
... I've described this at the URL:
http://www.cogsci.ed.ac.uk/~richard/pipeline.html[11]
Alex: This is a lot like what I do now.
Richard: Unlike Alex, I distinguish control structure from things that
happen in components.
... I wanted to make the control structure explicitly part of the
language.
... My aim is to find the smallest amount of control structure necessary.
... I think viewports, for example, don't have to be control structures.
Alex: Is this if/else or choose?
Richard: I've deliberately not answered that question. You could in
principle compile from a choose down to an if/else as I've described here.
Norm: I think the question of whether conditionals are part of the
language or just components is central.
... I'm leaning towards the idea that control structures should be in the
language
Richard: I wanted to avoid the case where a component took two pipelines
and a condition. This would be something like 'eval' and that makes things
less transparent.
ack
<Zakim> ht, you wanted to argue in favour of conditional-in-the-language
position
HT: I want to endorse the inclination that we should have conditionals in
the language
... Exposing conditionals as a language construct is important in order to
allow the analysis of pipelines to be a sensible thing to undertake.
... Knowning that there are exclusive "OR"s about is a potentially
important factor in analysis.
<MSM> Why not just say that the language does not guarantee either that
every component will run, nor that components in the false branch won't
run?
Norm: Anyone uncomfortable with conditionals as components-in-the language
MSM: Alex has argued in the past for the view that control structures
shouldn't be part of the language so that you can add new control
structures by adding new components
<ht> HST doesn't hear roll-your-own-control being ruled _out_, just
exposing conditionals as part of the language _in_
Richard: That raises the question of side effects.
MSM: There are programming languages that say "under these conditions
whether the side-effect is observable or not is undefined"
Richard: They say that about their basic conditional?
MSM: Yes.
MSM: In particular, boolean conditionals may be evaluated in some
indeterminate order, short circuited or not.
Some discussion of whether that's the same as the possible implementation
of the else branch
Alex: I have a bunch of developers using pipelines. I make no distinction
between steps and language constructs like choose and the viewports. My
impression is that they find this confusing.
... Implementation-wise, they're all components. But having conditionals
and viewports not part of the "higher language" constructs is confusing to
users.
... In the end, my choice to implement choose as a component is just an
implementation choice, no more.
... I make sure the "else" branches don't run.
<MSM> If what is being proposed is "let us define semantics for
conditional constructs as part of our spec", then I think I am OK with it.
I think that's what we're saying MSM
<MSM> As long as we're not saying "no component is allowed to do anything
but read input and write output" ...
HT: I don't propose to rule out components that perform conditionals, just
the positive aspect of making some conditionals part of the language.
MSM: I would have expected this to be a question of what's defined in our
spec, but we seem to be going a little further than just putting it in the
spec.
... I want it to be a language construct vs. I want conditionals to be
defined in our spec seems to be the issue.
Richard: Suppose that you didn't have an "if" and you wanted to implement
it as a component.
... This component would have to have inputs and etc., but also a
description of the "if" and "else" branches.
... So if we said that's how it worked, we'd have to make it possible for
pipelines to be parameters to components.
... This gives components a lot more power than we need to do the bare
minimum.
... I don't want the basic, minimal language to have to support that
complexity.
MSM: I guess I see some tension between what should be the minimum and
what should be possible.
<ht> Richard contrasts fexprs and macros in Lisp
Richard: I'm quite happy with something that works like a macro, something
that turns into some control structure using that. What I'm not happy with
is something that effectively "evals" its arguments to perform a
computation
Alex: I allow you to embed chunks of a pipeline in your components.
<MSM> Richard, can you type in the Lisp keyword / technical term you were
pronouncing?
<richard> FEXPR
Alex: An analogy here is XSLT instructions. If you want to write your own
instruction, you need to be able to embed other instructions inside it.
<richard> it's one the kinds of EXPR (expression)
Alex: In XSLT, that's completely implementation defined. It's an issue if
we need to go there or not.
<richard> you won't find it in scheme!
Alex: That's one way to give extensibility without having to reinvent the
world. You can invent your own crazy conditional with side effects or what
have you. But it does put additional requirements on implementors.
<MSM> Ah, that may be why it sounded unfamiliar
<richard> scheme takes the approach i'm advocating, it has macros but no
eval-like mechanism
<richard> And my point about viewports is that they can be implemented in
a macro-like manner without any "magic" components
<alexmilowski> yes.
<scribe> ACTION: MSM to setup bugzilla for us [recorded in
http://www.w3.org/2006/03/23-xproc-minutes.html#action05[12]]
Sub-pipelines
Norm: The ability to define and reuse a sub-pipeline in the same document
is still an open quesiton
Richard: If we accept the separation of the language into a conceptual
part and a syntax for expressing that, then this issue falls into the
second part.
... I think we're all agreed that conceptually you should be able to put a
sequence of steps anywhere that a component can occur
Norm: Do we all agree that conceptually you can put a sub-pipeline
anywhere you can put a component?
Some "yes"es, some "not sure"s
No "no"s
<MSM> it sounds right, but I keep worrying about a catch I'm not seeing.
<alexmilowski> (sorry... stepped off...) yes
Norm: Raising the question to the conceptual level seems to reduce the
urgency of answering the question
HT: But it does raise the urgency on the question of whether we're talking
about an abstract syntax with a nearly-isomorphic concrete syntax or if
we're designing an virtual machine with a concrete syntax that might be
quite removed
... The time is coming when we're going ot have to make our minds up
Richard: I think you're right, but the answer will be neither of the two
extremes
... The abstract primitives aren't a virtual machine, but they're designed
to make programming easier.
... They're more like the primitives of lisp that will be extended by
writing functions and macros on top of them
Any other business
Face-to-face in August in Toronto
Alex: Exact time is undecided
... But I'm willing.
Norm: Anyone uncomfortable with having another f2f this soon?
<MSM> which week in August?
Richard: I'm not sure I can make it, but the date doesn't have much
bearing.
HT: I think it's a good idea, I will try to come.
Norm: Please respond in email if you prefer 2-4 Aug or 14-17 Aug
Adjourned
Summary of Action Items
[NEW] ACTION: Alex to produce a draft with reordered use cases by 29 Mar
2006 [recorded in
http://www.w3.org/2006/03/23-xproc-minutes.html#action04[13]]
[NEW] ACTION: Alex: add a note to the effect that the table is incomplete
[recorded in http://www.w3.org/2006/03/23-xproc-minutes.html#action02[14]]
[NEW] ACTION: MSM to draft a complete table; ETA: 21 Apr 2006 [recorded in
http://www.w3.org/2006/03/23-xproc-minutes.html#action01[15]]
[NEW] ACTION: MSM to setup bugzilla for us [recorded in
http://www.w3.org/2006/03/23-xproc-minutes.html#action05[16]]
[NEW] ACTION: Norm to request first-public-working draft status [recorded
in http://www.w3.org/2006/03/23-xproc-minutes.html#action03[17]]
**
[End of minutes]
----------------------------------------------------------------------
[1] http://www.w3.org/
[2] http://www.w3.org/XML/XProc/2006/03/23-agenda.html
[3] http://www.w3.org/2006/03/23-xproc-irc
[4] http://www.w3.org/XML/XProc/2006/03/23-agenda.html
[5] http://www.w3.org/XML/XProc/docs/langreq.html#use-cases
[6] http://www.w3.org/2006/03/23-xproc-minutes.html#action01
[7] http://www.w3.org/2006/03/23-xproc-minutes.html#action02
[8] http://www.w3.org/2006/03/23-xproc-minutes.html#action03
[9] http://www.w3.org/2006/03/23-xproc-minutes.html#action04
[10] http://www.cogsci.ed.ac.uk/~richard/pipeline.html
[11] http://www.cogsci.ed.ac.uk/~richard/pipeline.html
[12] http://www.w3.org/2006/03/23-xproc-minutes.html#action05
[13] http://www.w3.org/2006/03/23-xproc-minutes.html#action04
[14] http://www.w3.org/2006/03/23-xproc-minutes.html#action02
[15] http://www.w3.org/2006/03/23-xproc-minutes.html#action01
[16] http://www.w3.org/2006/03/23-xproc-minutes.html#action05
[17] http://www.w3.org/2006/03/23-xproc-minutes.html#action03
[18] http://dev.w3.org/cvsweb/~checkout~/2002/scribe/scribedoc.htm
[19] http://dev.w3.org/cvsweb/2002/scribe/
Minutes formatted by David Booth's scribe.perl[18] version 1.127 (CVS
log[19])
$Date: 2006/03/28 19:40:49 $
Received on Tuesday, 28 March 2006 19:42:30 UTC