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Subject: RE: [sca-assembly] ISSUE 6: usage of not promoted references
Just to make a summary - it seems the text & the proposal are accepted,
and the only exception is what should happen in case there is reference
with multiplicity 1..1 or 1..n , however it is not wired. Initially that
was proposed as deployment error, however since both Dave & MR seems to
prefer a runtime error during the first usage to the component, the
proposal is updated to reflect their opinion.
Btw, I would assume the same behavior should happen in case the target
of the reference is component, which is invalid. Since the same
arguments can apply (the target component may come as later
contribution), then there should be NO deployment error and the same
runtime error during the first usage should happen.
@Dave & Michael -- what's your opinion on this & do you think that we
should add a text about that case in the proposal or that is another
issue ?
PROPOSAL
The following description should be added in section 1.6.2
References, after line 1387 (that line is after the paragraph that
explains attaching a binding to a reference and before the
paragraph
explaining callback) :
Promotion of references accessing endpoints via bindings is
suggested practice since it allows the assembler to change the
targets of the references or the specified bindings and encourages
component reuse, however the lack of such promotion by itself
MUST
NOT cause errors during deployment or runtime if the target of the
reference can be identified. The assembler is expected to
guarantee
for an unpromoted reference with multiplicity 1..1 or 1..n that
one
of the following conditions holds : there is either internal wire
within the scope of the current composite or a binding that
identifies correctly either the component/service for a wire to an
endpoint within the SCA domain or the accessible address of some
endpoint outside the SCA domain. If the assembler does not
provide
these conditions for a reference that has a multiplicity of 1..1
or
1..n, then such an unresolved reference MUST generate a runtime
error
at latest during the first attempt to use the component.
If the assembler does not provide these conditions for a
reference that has a multiplicity with 0..1 or 0..n , then the
programming model MUST not generate deployment errors and the
reference's wiring state will be represented in accordance to the
implementation type in question (e.g. null, handle that throws
exceptions when accessed, extensibility hooks, etc.).
For example the following definitions MUST NOT generate deployment
error
:
<composite xmlns="http://www.osoa.org/xmlns/sca/1.0";
name="MyValueComposite">
<component name="MyValueServiceComponent">
<implementation.java
class="services.myvalue.MyValueServiceImpl"/>
<reference name="StockQuoteService">
<binding.ws uri=",http://www.sqs.com/StockQuoteService"/>
</reference>
<reference name="StockQuoteService2">
<binding.jms>
<destination name="StockQuoteServiceQueue"/>
<connectionFactory name="StockQuoteServiceQCF"/>
</binding.jms>
</reference>
</component>
<!-- no references and promotion on purpose -->
<composite>
however the following definitions MUST generate one :
<composite xmlns="http://www.osoa.org/xmlns/sca/1.0";
name="MyValueComposite">
<component name="MyValueServiceComponent">
<implementation.java
class="services.myvalue.MyValueServiceImpl"/>
<reference name="UnwiredReference">
<!-- the target cannot be determined, that should
be
an
error-->
<binding.ws/>
</reference>
</component>
<!-- no references and promotion on purpose -->
<composite>
-----Original Message-----
From: David Booz [mailto:booz@us.ibm.com]
Sent: Saturday, 27. October 2007 00:18
To: sca-assembly@lists.oasis-open.org
Cc: Blohm, Henning; Martin Chapman; Michael Rowley
Subject: RE: [sca-assembly] ISSUE 6: usage of not promoted references
I agree with Mike R's comments.
I don't think we should complicate multiplicity. In my mind, your
second
and third cases are not distinct because they occur at different points
in
the lifecycle of the composite. I think we should assert that it is
just
not possible to detect an error in these cases until the component
owning
the reference is started/initialized/dispatched (whatever word you want
to
use, they are all the same to me). That is, I don't think we should
attempt to support your 3rd point.
A batch deployment mechanism with special validation semantics sounds
like
an interesting vendor extension. Since this kind of extended behavior
effectively constrains what can be successfully deployed, it doesn't
make
the app incompatible with a vendor that doesn't do batch deploy +
validation.
Dave Booz
STSM, SCA and WebSphere Architecture
Co-Chair OASIS SCA-Policy TC
"Distributed objects first, then world hunger"
Poughkeepsie, NY (845)-435-6093 or 8-295-6093
e-mail:booz@us.ibm.com
http://washome.austin.ibm.com/xwiki/bin/view/SCA2Team/WebHome
"Peshev, Peter"
<peter.peshev@sap
.com>
To
"Michael Rowley"
<mrowley@bea.com>,
10/24/2007 02:00 "Martin Chapman"
PM? <martin.chapman@oracle.com>,
"Blohm, Henning"
<henning.blohm@sap.com>, "OASIS
Assembly"
<sca-assembly@lists.oasis-open.org>
cc
Subject
RE: [sca-assembly] ISSUE 6: usage
of not promoted references
Hi Michael,
Thanks very much for the clarification, now I understood what you had
in
mind.>,
Do you think that would lead to a new option for multiplicity (maybe
raised
as another issue ) ?
Since it seems we are wanting to cover 3 scenarios in case the target is
unavailable
-- error during first use of the reference (the 0..1)
-- error during first instantiation of component (what you are
suggesting
for 1..1 in order to solve the bulk deployment for cross-referenced
components)
-- error during deployment (1..1 in the current proposal, and what
probably many people would expect.
I.e. even if such spec expert as you thought for a moment this is the
1..1 meaning, than obviously the mortal guys (me & the assemblers) may
be
thinking the same meaning as well :)
Best Regards
Peter
From: Michael Rowley [mailto:mrowley@bea.com]
Sent: Wednesday, 24. October 2007 20:32
To: Peshev, Peter; Martin Chapman; Blohm, Henning; OASIS Assembly
Subject: RE: [sca-assembly] ISSUE 6: usage of not promoted references
From: Peshev, Peter [mailto:peter.peshev@sap.com]
Sent: Wednesday, October 24, 2007 12:40 PM
To: Martin Chapman; Blohm, Henning; Michael Rowley; OASIS Assembly
Subject: RE: [sca-assembly] ISSUE 6: usage of not promoted
references
HI Michael,
Since the old text got too much inlined and I am usually confused
with that, I will try to summarize the opened sub-issues.
- you are saying
"Having 1..1 instead of 0..1 could mean that an error should be
generated at runtime, possibly at the first use of the component "
That indeed contradicts the proposal, however I have formed the
proposal entirely based on your input to the issue on 5th of
October,
where you have stated explicitly :
"If the reference has a multiplicity of 1..1 or 1..n, then such an
unresolved reference should generate a deployment error."
You got me there. I guess I didn't concentrate very closely before on
deploy vs. runtime for this error.
Maybe I have misunderstood you & the intention for 0..1, sorry for
that , but that only shows that the issue is valid and it needs
clarification :).
I personally believe that the initial suggestion based on your
email
(deployment exception for unwired reference with 1..1) is better
for
the assembler who is alarmed immediately of wiring problems at
deployment, instead of deferring them to the first runtime
invocation. Often applications are complex and the assembler would
have very hard time verifying each possible path of the business
logic (full cyclomatic complexity search) to check for such
unwired
references and whether everything is working. That feature at
least
to me seems more valuable than covering the use case of having A
wired to B via reference X with 1..1, B wired to A via reference Y
with 1..1, A is deployed as single contribution, afterwards B is
deployed as single contribution.
In addition if we delay the exception at runtime in the 1..1 case,
I
am still lost what exactly is the difference between 0..1 and
1..1.
In both cases we will allow deployment if there is no target for
the
reference, in both cases there will be exception at runtime if the
target is still not available, and in both cases if there is
target
the call will pass.
The difference is that in the 1..1 case the error will be raised on the
first use of the component, not on the first use of that reference (that
way you don't have to wait until the reference is used before getting
your
NullPointerException, or whatever it is).
I'd be OK with generating the error at deployment time if we invented
some
means of doing batch deployment - to tell the system not to do its
checks
until a group of related deployments are all complete. However, writing
up
such a mechanism would be a bit more work.
Back to some other raised issues and raised points:
- I have changed the first sentence in the way you have
suggested,
also specified that it's neither in runtime nor in deployment
there
will be errors. Thanks for the suggestion
Great.
- The MUST in the last sentence is not bringing enough
information,
very good point. I switched it to use "will be represented" and
added mentioning of the extensibility hooks.
I like that.
So here is the new
PROPOSAL :
I like the new proposal, except the fact that it creates a need for some
kind of bulk deployment mechanism, as noted above.
Michael
The following description should be added in section 1.6.2
References, after line 1387 (that line is after the paragraph that
explains attaching a binding to a reference and before the
paragraph
explaining callback) :
Promotion of references accessing endpoints via bindings is
suggested practice since it allows the assembler to change the
targets of the references or the specified bindings and encourages
component reuse, however the lack of such promotion by itself
MUST
NOT cause errors during deployment or runtime if the target of the
reference can be identified. The assembler is expected to
guarantee
for an unpromoted reference with multiplicity 1..1 or 1..n that
one
of the following conditions holds : there is either internal wire
within the scope of the current composite or a binding that
identifies correctly either the component/service for a wire to an
endpoint within the SCA domain or the accessible address of some
endpoint outside the SCA domain. If the assembler does not
provide
these conditions for a reference that has a multiplicity of 1..1
or
1..n, then such an unresolved reference MUST generate a deployment
error. If the assembler does not provide these conditions for a
reference that has a multiplicity with 0..1 or 0..n , then the
programming model MUST not generate deployment errors and the
reference's wiring state will be represented in accordance to the
implementation type in question (e.g. null, handle that throws
exceptions when accessed, extensibility hooks, etc.).
For example the following definitions MUST NOT generate deployment
error
:
<composite xmlns="http://www.osoa.org/xmlns/sca/1.0";
name="MyValueComposite">
<component name="MyValueServiceComponent">
<implementation.java
class="services.myvalue.MyValueServiceImpl"/>
<reference name="StockQuoteService">
<binding.ws uri=",http://www.sqs.com/StockQuoteService"/>
</reference>
<reference name="StockQuoteService2">
<binding.jms>
<destination name="StockQuoteServiceQueue"/>
<connectionFactory name="StockQuoteServiceQCF"/>
</binding.jms>
</reference>
</component>
<!-- no references and promotion on purpose -->
<composite>
however the following definitions MUST generate one :
<composite xmlns="http://www.osoa.org/xmlns/sca/1.0";
name="MyValueComposite">
<component name="MyValueServiceComponent">
<implementation.java
class="services.myvalue.MyValueServiceImpl"/>
<reference name="UnwiredReference">
<!-- the target cannot be determined, that should
be
an
error-->
<binding.ws/>
</reference>
</component>
<!-- no references and promotion on purpose -->
<composite>
Best Regards
Peter
From: Martin Chapman [mailto:martin.chapman@oracle.com]
Sent: Wednesday, 24. October 2007 19:24
To: Blohm, Henning; 'Michael Rowley'; 'OASIS Assembly'
Subject: RE: [sca-assembly] ISSUE 6: usage of not promoted
references
do i smell some confromance targets here...what do we (abstractly)
install and to what, and where do we deploy it?
-----Original Message-----
From: Blohm, Henning [mailto:henning.blohm@sap.com]
Sent:, Wednesday, October 24, 2007 4:46 PM
To: Michael Rowley; OASIS Assembly
Subject: AW: [sca-assembly] ISSUE 6: usage of not promoted
references
Michael,
on the deployment error issue. In SCA we seemed to use the term
deployment as "making available to process requests" and used the
additional term "installation" for getting something into the
system.
Reading deployment as "making available to process requests" it
is
very close to "use" in which case you and Peter seem to talk
about
the same point in time.
It could be best if the assembly spec would include some
wording
to describe the exact meaning of "deploy" and "install". You
agree?
Thanks,
Henning
Von: Michael Rowley [mailto:mrowley@bea.com]
Gesendet: Mittwoch, 24. Oktober 2007 15:28
An: OASIS Assembly
Betreff: RE: [sca-assembly] ISSUE 6: usage of not promoted
references
[MR: inline]
-----Original Message-----
From: Peshev, Peter [mailto:peter.peshev@sap.com]
Sent: Wednesday, October 24, 2007 3:26 AM
To: Michael Rowley; OASIS Assembly
Subject: RE: [sca-assembly] ISSUE 6: usage of not promoted
references
HI Michael,
Comments inline, I have pasted your issues with ">"
>- First, "RECOMMENDED" and "NOT REQUIRED" are not a
defined
keywords.
PP : There is no ""RECOMMENDED" in this proposal. In
addition
when
looking at http://www.ietf.org/rfc/rfc2119.txt RECOMMENDED
and REQUIRED
are mentioned as key words.
[MR: Good point on RECOMMENDED (I had originally written just
"NOT
REQUIRED", but then belatedly (and incorrectly) added
"RECOMMENDED"
when I happened to see it - apparently when I was looking too far
down in the email to the old proposal). Regarding "NOT REQUIRED"
-
yes "REQUIRED" is a keyword, and "MUST NOT" is also a key phrase,
but "NOT REQUIRED" is not.]
Anyway as per the notes of the OpenCSA
Steering Committee Minutes from 28 September the keyword
SHOULD and
its synonym RECOMMENDED are supposed to be avoided, and
only
the rest of
the keywords remain to be used. However being a developer I
don't claim
any competence in speac creation, so maybe you are right.
> In particular, the bit that says that "an implementation
which does
not include a particular option MUST be prepared to
interoperate with
...". What does that mean when the "implementation" is the
assembler?
PP : At least my understanding of the keyword usage is
that
they should
be used whenever there is requirement towards the SCA
Runtime
(i.e. the
vendors that will implement the spec), and not to be used
for
any users
of the spec -- assembler, deployer, etc. That's what was
supposed to be
in the proposal, If something is not done in that way, I
will
be glad to
fix.
if the first sentence is not clear enough, maybe we can
adapt
it to :
Promotion of references accessing endpoints via bindings is
common
practice since it allows the assembler to change the
targets
of the
references or the specified bindings and encourages
component
reuse,:
however the lack of such promotion MUST NOT cause error in
SCA
Runtime-s
.
[MR: I think it is worthwhile to say that promotion is
recommended
(lowercase). I think it is very valuable for the specification
to
include directives and suggestions to our various human roles.
Changing the MUST NOT to be on the runtime seems better, but
perhaps
it should be on deployment, as in "lack of promotion MUST NOT
cause
an error during deployment."]
>- I suspect that we should not REQUIRE that a deployment
error be
generated for unwired 1..1 references. Consider what would
happen if
someone developed deployable composites A and B (each from
different
contributions) with the intention of wiring at least one of
the
components from A to something in B and wiring at least one
component in
B to something in A. There would be no legal ordering of
the
deployments, as the first deployment would always fail.
PP : Yes, it will be an error. In that case the assembler
should use
0..1 if he wants to deploy the first component and after
some
time the
other. Isn't this exactly what 0..1 was intended for ?
Otherwise what is
the difference between 0..1 and 1..1 ?
[MR: Having 1..1 instead of 0..1 could mean that an error should
be
generated at runtime, possibly at the first use of the component
that includes that reference, rather than at deployment time. It
would be unfortunate for someone to have to declare a reference
that
is really required as 0..1 just to get around deployment order
issues.]
>- The last MUST, which is on the programming model, says:
"MUST
represent the reference's wiring state in accordance to the
implementation type in question". Presumably Peter meant
to
include the
words "as invalid" after the word "state". However, even
with
this
modification I don't like the requirement. SCA is intended
to
be an
integration technology, which means that it needs to be
able
to
accommodate a wide variety of implementation types. Some
of
these
implementation types will use programming models where
external services
can be used, but some kind of default behavior occurs if
one
isn't
(think of extensibility hooks). Such a programming model
should be able
to represent these as references to SCA, in spite of the
fact
that they
don't follow the admonition that unwired references be
presented as
nulls.
PP : The wording "according to the implementation type in
question" was
supposed to cover the "wide variety of implementation
types"
that you
are speaking. If you prefer some other wording I would be
glad
to
include. Maybe mentioning explicitly extensibility hooks
if
you
consider them so important :
... MUST NOT generate deployment errors and MUST represent
the
reference's wiring state in accordance to the
implementation
type in
question (e.g. null,
handle that throws exceptions when accessed, extensibility
hooks, etc.).
[MR: I was reacting against this on the assumption, apparently
incorrect, that the words "as invalid" had been removed
accidentally, since the current sentence doesn't seem to make any
sense. I read the current wording as saying "the programming
model
MUST represent the reference however it wants." What kind of a
requirement is that?]]
Michael
Best Regards
Peter
________________________________
From: Michael Rowley [mailto:mrowley@bea.com]
Sent: Tuesday, 23. October 2007 20:54
To: Peshev, Peter; OASIS Assembly
Subject: RE: [sca-assembly] ISSUE 6: usage of not promoted
references
I'll comment on the RFC 2119 usage, which I had hoped to
avoid, but I we,
have to address it at some point, so we might as well start
with this
proposal.
- First, "RECOMMENDED" and "NOT REQUIRED" are not a defined
keywords.
If we changed it to use the closest defined keyword ("MAY")
it
might be
something like "The assembler MAY promote references...",
but
that would,
be odd, given the definition of MAY according to 2119:.
5. MAY This word, or the adjective "OPTIONAL", mean that
an
item is
truly optional. One vendor may choose to include the
item
because a
particular marketplace requires it or because the vendor
feels that
it enhances the product while another vendor may omit
the
same item.
An implementation which does not include a particular
option MUST be
prepared to interoperate with another implementation
which
does
include the option, though perhaps with reduced
functionality. In the,
same vein an implementation which does include a
particular
option
MUST be prepared to interoperate with another
implementation which
does not include the option (except, of course, for the
feature the
option provides.)
In particular, the bit that says that "an implementation
which
does not
include a particular option MUST be prepared to
interoperate
with ...".
What does that mean when the "implementation" is the
assembler?
- I suspect that we should not REQUIRE that a deployment
error
be
generated for unwired 1..1 references. Consider what would
happen if
someone developed deployable composites A and B (each from
different
contributions) with the intention of wiring at least one of
the
components from A to something in B and wiring at least one
component in,
B to something in A. There would be no legal ordering of
the
deployments, as the first deployment would always fail.
- The last MUST, which is on the programming model, says:
"MUST
represent the reference's wiring state in accordance to the
implementation type in question". Presumably Peter meant
to
include the,
words "as invalid" after the word "state". However, even
with
this
modification I don't like the requirement. SCA is intended
to
be an
integration technology, which means that it needs to be
able
to
accommodate a wide variety of implementation types. Some
of
these
implementation types will use programming models where
external services,
can be used, but some kind of default behavior occurs if
one
isn't
(think of extensibility hooks). Such a programming model
should be able,
to represent these as references to SCA, in spite of the
fact
that they
don't follow the admonition that unwired references be
presented as
nulls.
Michael
-----Original Message-----
From: Peshev, Peter [mailto:peter.peshev@sap.com]
Sent: Tuesday, October 23, 2007 12:31 PM
To: OASIS Assembly
Subject: RE: [sca-assembly] ISSUE 6: usage of not promoted
references
Once again, replacing the funny idea of :
"reference with reference 1..1 or 1..n"
with the intended wording. Otherwise everything is the
same.
Sorry :(
PROPOSAL :
The following description should be added in section 1.6.2
References,
after line 1387 (that line is after the paragraph that
explains
attaching a binding to a reference and before the paragraph
explaining
callback) :
Promotion of references accessing endpoints via bindings is
common
practice since it allows the assembler to change the
targets
of the
references or the specified bindings and encourages
component
reuse,
however it is NOT REQUIRED. The assembler is expected to
guarantee for
an unpromoted reference with multiplicity 1..1 or 1..n that
one of the
following conditions holds : there is either internal wire
within the
scope of the current composite or a binding that
identifies
correctly
either the component/service for a wire to an endpoint
within
the SCA
domain or the accessible address of some endpoint outside
the
SCA
domain. If the assembler does not provide these conditions
for a
reference that has a multiplicity of 1..1 or 1..n, then
such
an
unresolved reference MUST generate a deployment error. If
the
assembler
does not provide these conditions for a reference that has
a
multiplicity with 0..1 or 0..n , then the programming model
MUST not
generate deployment errors and MUST represent the
reference's
wiring
state in accordance to the implementation type in question
(e.g. null,
handle that throws exceptions when accessed, etc.).
For example the following definitions MUST NOT generate
deployment error,
:
<composite xmlns="http://www.osoa.org/xmlns/sca/1.0";
name="MyValueComposite">
<component name="MyValueServiceComponent">
<implementation.java
class="services.myvalue.MyValueServiceImpl"/>
<reference name="StockQuoteService">.
<binding.ws
uri="http://www.sqs.com/StockQuoteService"/>
</reference>
<reference name="StockQuoteService2">
<binding.jms>
<destination name="StockQuoteServiceQueue"/>
<connectionFactory name="StockQuoteServiceQCF"/>
</binding.jms>
</reference>
</component>
<!-- no references and promotion on purpose -->
<composite>
however the following definitions MUST generate one :
<composite xmlns="http://www.osoa.org/xmlns/sca/1.0";
name="MyValueComposite">
<component name="MyValueServiceComponent">
<implementation.java
class="services.myvalue.MyValueServiceImpl"/>
<reference name="UnwiredReference">
<!-- the target cannot be determined, that
should be an,
error-->
<binding.ws/>
</reference>
</component>
<!-- no references and promotion on purpose -->
<composite>
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