- From: Norman Walsh <Norman.Walsh@Sun.COM>
- Date: Tue, 02 May 2006 10:36:03 -0400
- To: public-xml-processing-model-wg@w3.org
- Message-ID: <87d5ewo5nw.fsf@nwalsh.com>
[ Scribe apologizes for tardiness. ]
See http://www.w3.org/XML/XProc/2006/04/27-minutes.html
W3C[1]
- DRAFT -
XML Processing Model WG
27 Apr 2006
Agenda[2]
See also: IRC log[3]
Attendees
Present
Alex, Alessandro, Norm, Paul, Richard, Mohamed, Henry, Michael,
Murray [xx:16-]
Regrets
Andrew
Chair
Norm
Scribe
Norm
Contents
* Topics
1. Accept this agenda?
2. Accept minutes from the previous teleconference?
3. Next meeting: 4 May telcon
4. Issue 3096: Are components side-effect free?
5. Issue 3113: Does the pipeline engine act as a resource manager?
* Summary of Action Items
----------------------------------------------------------------------
Accept this agenda?
-> http://www.w3.org/XML/XProc/2006/04/27-agenda.html
Accepted
Accept minutes from the previous teleconference?
-> http://www.w3.org/XML/XProc/2006/04/20-minutes.html
Accepted
Next meeting: 4 May telcon
Any regrets?
<MoZ> yes
Face-to-face meeting?
Registration page: http://www.w3.org/2002/09/wbs/38398/XProcFTF2/[6]
Issue 3096: Are components side-effect free?
-> http://www.w3.org/Bugs/Public/show_bug.cgi?id=3096
Norm proposes:
I propose that we say that all components are non-functional. That is,
a pipeline implementation must behave as if it evaluated a component
every time it occurs. "Must behave as if" is spec-ease for
"implementations that are clever enough to determine with certainty
that a component is, in fact, functional are free to cache the
intermediate results because by golly if it is, no one will be able to
Richard: This doesn't preclude adding a mechanism later to allow authors
to assert that a step or component is functional
Norm: Yes.
Richard: Does this address the converse case? Producing output
side-effects and behaving the same way for given inputs
Norm: This is the "functional" aspect, not the side-effect aspect
Richard: Side-effects are like hidden outputs, functionality is like
hidden inputs
Alex: This is a good place to start, register a new issue about functional
components?
<scribe> ACTION: Alex to create an issue about the possibility of
functional components [recorded in
http://www.w3.org/2006/04/27-xproc-minutes.html#action01[8]]
Proposal accepted.
Issue 3113: Does the pipeline engine act as a resource manager?
-> http://www.w3.org/Bugs/Public/show_bug.cgi?id=3113
Norm: One aspect of this question is, does the pipeline engine provide the
sort of URI-stability that XSLT, for example, gives the document function
Richard: I strongly disagree with this as a requirement; it requires a
degree of intimacy between the engine and the components that may not
always be available
Alex: Is this something that might be "at user option"
Norm: I'd like to avoid that if at all possible
<Zakim> ht, you wanted to push back
Henry: I need some information; in my current state of knowledge I think
it's a bad idea for pipeline engines
... Especially when you are running a pipeline engine as a server, you do
not want to flush the cache everytime you run a pipe because it's useful
to keep things around.
... In their parsed and ready-to-go state (provided they haven't changed)
... I'm happier saying, "no, you should expect your pipeline to behave in
the way of any other web application does"
... Yes, things can change.
Alex: If we step back and look at the web browser case, consider an image
embedded 10 times on the same page. The browser reuses the image.
... The resolution of URI-to-resource is stable for the duration of a page
is one reasonable expectation
<MSM> [I think the fact that browser do or do not re-fetch is an
optimization they make, not part of the specification of correct browser
behavior - am I wrong?]
Richard: consider other things like XML pipelines, like shell scripts,
where "cat foo" twice might not return the same file.
<MSM> [If ten <img> elements in the same HTML document refer to
"my_image.jpg", and that image is served with a lifetime of 0, are correct
browsers guaranteed to fetch it only once? What spec says that?]
Some discussion of whether or not browsers actually behave that way
<Zakim> MSM, you wanted to say that as an empirical statement, it's not a
very strong argument for making the behavior part of our spec
MSM: Implementors will do that for performance reasons regardless of
whether a spec requires it or not
Richard: Is there a spec for how you display things in a web page?
Alex: No
MSM: In that sense, it's not clear to me that the browser analogy bears on
our decision
Alex: There's a user expectation of some aspect of stability
Richard: I don't think the browser analogy is a good one. The engine is
running a collection of potentially independently implemented components.
Murray: I'm relying on my memory, but in HTTP there's a mechanism for
specifying time-to-live. So if there's a nano-second TTL, then maybe it
would go get the resource again.
... Similarly, if I was getting the time of day from a URI then it might
change
... So if you're worried about that, maybe you need a "caching" component.
Norm: I think consensus is coming towards the answer "no"
Alex: I don't agree, I think it's important that URIs are stable for the
duration of an execution
... If you need to identify unique resources, you can generate unique URIs
with query parameters
... We haven't decided if the resources flowing through the pipeline have
URIs or not
Richard: I notice that the bug is actually talking about something
produced by the pipeline
Norm: I think those are the same case
Richard: You could provide components that fetch and store URIs stably.
Norm describes the situation where an XSLT needs to get an ancillary
resource by URI
Alex: I really want some URIs to be stable throughout the duration of a
pipeline
Murray: I'm not convinced that we don't need a resource manager
... I'd like to posit the existence of a component that is a proxy server
or something of that ilk
... That component knows if requests should always send things back from
the cache
<MSM> [I agree fervently that as users we need resource managers, and that
implementations of our language will be more usable if they use good
resource managers. But we also need character sets. We don't specify a
character set as part of our spec to meet that need, and the same should
probably hold for resource management. Separate problem, separate spec.]
Murray: I think it's the case that sometimes you're going to want the
documents to remain stable and sometimes you're going to want to get
current results
<alexmilowski> yes!
Richard: But I may be using components that don't know how to use a proxy
server
Murray: I thought once you setup a proxy, then all requests went through
that proxy.
That's implementation and operating-system dependent
Richard: Proxies do give a degree of generality that seems nice
MSM: I'm not sure I'm understanding everything going on here. I agree that
being able to cache and being able to gaurantee up-to-date resources are
good things
... But lots of these things seem to be not terribly closely related to
pipelines any more than we need a character set.
... We just rely on getting character sets from lower layers.
... Building it into the pipeline engine strikes me as a breach of
orthogonality.
... At least for the components that we require an implmentation provide,
we can say what the answers are or say that they're implementation defined
Murray: I think you're thinking of it in terms of the pipeline language
and not the overall processing model. If you're processing large volumes
of XML, you may want a proxy server that has access to pipeline
descriptions so that all your documents can be passed through.
<richard> Beware of assuming that everything comes through HTTP. What if
they're just files?
Indeed. The proxy has to handle file: URIs as well.
MSM: It should be orthogonal. If I've got a caching proxy installed, I
want my pipeline engine to use that one, not one that it felt it needed to
build in.
Alex: The document function in XSLT gets the resource through the local
environment that might use a local cache
MSM: The only thing the XSLT language says is that if you call the
document function with the same URI, you'll get the same document
Alex: You want to be able to compare the objects you get back from the
document function.
... Do we really have the requirement that things behave this way across
components?
Richard: I think that Alex has drawn attention to an important point. XSLT
can do this because it only says the document function behaves this way.
... Are we really going to say that if the stylesheet is a file: URI then
it can't just open it?
Murray: In a shell script, you'd handle this by copying it and then
referring to the copy.
Richard: Yes, and if you were using a program that had the name hard
coded, then you couldn't make it use the copy
Norm attempts to summarize the consensus which remains "no"
HT: The discussion we've had has been drawn somewhat more narrowly than
the first sentenc of the actual issue.
<MSM> [I wonder if there is consensus on the proposition that in cases
like the example given by Norm in raising the issue, it *is* our
responsibility to say whether the data stream written to uri Foo is or is
not guaranteed the same as the data stream (later) read from uri Foo]
HT: We've discussed in the past the use of pipeline engines as resource
managers.
... Consider output="#foo" somewhere and input="#foo" somewhere else in a
pipeline.
... One way to think about that is that the engine is managing those
resources.
... I don't believe that issue is off the table because of this discussion
Norm: I agree
<MSM> I'm a little puzzled / troubled here. If I interpret output="#foo"
and input="#foo" as references to resources to be managed by the pipeline,
then I suddenly have an ambiguity I didn't use to have:
<MSM> does the input stream read the ouptut stream?
<MSM> or is this a pipeline which reads resource #foo, does something with
it, and writes it back?
Scribe lost the thread
<MSM> ht, I wonder if you can expound on how you would propose avoiding
this ambiguity
<ht> So I think Richard just expressed the dichotomy in an interesting way
-- do we name ports, or infosets
<MSM> +1: Richard's formulation of the question is an acute one
ADJOURNED
Summary of Action Items
[NEW] ACTION: Alex to create an issue about the possibility of functional
components [recorded in
http://www.w3.org/2006/04/27-xproc-minutes.html#action01[10]]
**
[End of minutes]
----------------------------------------------------------------------
[1] http://www.w3.org/
[2] http://www.w3.org/XML/XProc/2006/04/27-agenda.html
[3] http://www.w3.org/2006/04/27-xproc-irc
[6] http://www.w3.org/2002/09/wbs/38398/XProcFTF2/
[8] http://www.w3.org/2006/04/27-xproc-minutes.html#action01
[10] http://www.w3.org/2006/04/27-xproc-minutes.html#action01
[11] http://dev.w3.org/cvsweb/~checkout~/2002/scribe/scribedoc.htm
[12] http://dev.w3.org/cvsweb/2002/scribe/
Minutes formatted by David Booth's scribe.perl[11] version 1.127 (CVS
log[12])
$Date: 2006/05/02 14:32:48 $
Received on Tuesday, 2 May 2006 14:36:15 UTC