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Subject: Re: [sca-assembly] Summarizing the state of ASSEMBLY-235
- From: Mike Edwards <mike_edwards@uk.ibm.com>
- To: OASIS SCA Assembly <sca-assembly@lists.oasis-open.org>
- Date: Wed, 23 Feb 2011 11:42:41 +0000
Eric,
<eej>
You seem to want it both ways - since it is outside of SCA, we don't control
it and shouldn't (and yet the current spec attempts to), and yet you expect
my proposal to define how to constrain such outside interface definitions?
I'll turn this around. What constraint do you wish to see defined on the
OASIS CSA defined interfaces (interface.wsdl, interface.java - there are
no others, right?) that my proposal discards? I could easily wrap up this
proposal if I understand that.
</eej>
No - I am not wanting it both ways at
all.
I am concerned about what the SCA specifications
should say.
The SCA specifications are primarily
concerned with what is standardized.
Clearly, any extension such as a new
implementation type or a new interface type is outside the scope of the
current standards.
What we DO say is how new implementation
types and interface types should be added into a composition.
On the other hand, at the moment, the
only way of getting to some level of portability and interoperability for
a new implementation
type or a new interface type is to define
a specification for that new type - and this should ideally be done in
some OASIS TC.
Now, if the question is about what should
apply to a new STANDARDIZED interface type, then:
a) I am OK with the current wording
in the Assembly spec - it appears that you are not.
b) If you want to change the wording
in the Assembly spec, then I am asking what wording is intended to be there
that addresses this
issue of how we
can ensure that any (future) standardized interface type is interoperable
and portable.
I don't think that what I am asking
for is unreasonable. The current wording is clear, if unacceptable
to you.
However, I have not yet seen a proposal
for a change that gives any guarantee of portability and interoperability
for some new
standardized interface type. Hence
my comments about things "being left up to the SCA runtime",
which I think is a bad idea.
For stuff that is NOT standardized,
I don't think that the SCA specs can say very much. We do have the
material about conformance
demanding that IF an SCA runtime chooses
to claim conformance on the basis of a non-standard implementation type,
that certain
things are required - namely documentation
and the passing of an adapted test suite, but that only relates to conformance
claims.
I note that if an SCA runtime supported
<implementation.java/> and <implementation.foo/>, then currently
we make very few
demands on <implementation.foo/>
if the runtime is not claiming conformance on the basis of implementation.foo.
I think the same
can be said for <interface.foo/>.
So my concern is for any (future) interface
types that may need standardizing for the purposes of interoperability
and portability.
I think that there should be some wording
to address this. And it has to be the Assembly spec that holds those
words since I think
that the Assembly spec is the place
that binds all these things together.
Meanwhile for non-standardized stuff,
what force do the words in the Assembly spec carry? Very little in
my opinion.
PS we have interface.c & interface.cpp
defined in the current specifications
Yours, Mike
|
|
Dr Mike Edwards
| Mail Point 146, Hursley
Park
|
|
STSM
| Winchester, Hants SO21
2JN
|
SCA & Services
Standards
| United Kingdom
|
Co-Chair OASIS SCA
Assembly TC
|
|
|
IBM Software Group
|
|
|
Phone:
| +44-1962 818014
|
|
|
Mobile:
| +44-7802-467431 (274097)
|
|
|
e-mail:
| mike_edwards@uk.ibm.com
|
|
|
|
|
From:
| Eric Johnson <eric@tibco.com>
|
To:
| Mike Edwards/UK/IBM@IBMGB
|
Cc:
| OASIS SCA Assembly <sca-assembly@lists.oasis-open.org>
|
Date:
| 23/02/2011 00:49
|
Subject:
| Re: [sca-assembly] Summarizing the state
of ASSEMBLY-235 |
Hi Mike,
You say:
<mje>
My observation is that if you are considering things that are simply proprietary
to a single vendor, then you can do virtually as you wish - this can be
outside any standard, since standards are all about portability and interoperability.
Here you are painting a scenario which involves neither portability nor
interoperability, so why do the SCA specifications matter?
</mje>
<eej>
And yet, the current spec does not read that way. It says (6.2.1 #6):
"for checking the compatibility of 2 remotable interfaces which are
in different interface languages, both are mapped to WSDL 1.1 (if not already
WSDL 1.1) and compatibility checking is done between the WSDL 1.1 mapped
interfaces." This is a definition that gets used normatively in MUST
level assertions.
As I interpret your statement, you're saying that the implementation is
free to ignore this definition in the context of ASM80011, for example,
because one or or other of the interfaces happen to be specific to a vendor?
Then we agree! ;-)
I guess the difference is that I want the normative language of the spec
to reflect this, rather than confuse the reader as to our intent.
</eej>
<mje>
The simple answer is: you can do as you please within TIBCO. Help
yourselves. The specs don't prevent this. There are no issues
that I can see.
Of course, I argue that it would be a good idea even for TIBCO to write
down the mapping they intend to use between tibcoWSDL20 and tibcoJMX, otherwise
the TIBCO customers might get confused. However, that is no concern
to the OASIS SCA specifications.
My concern is if ever it is expected that these different interface types
are expected to work across SCA runtimes from different vendors. In
that case there is a need to define how things are supposed to work. Please
give me an idea of what you would put into the SCA specifications to cover
this.
</mje>
<eej>
Well, except I believe that the spec doesn't read this way, or I would
not have spent all this time trying to clarify the spec. The spec very
clearly says that different interface type languages, if "remotable"
and considered for compatibility, MUST map to WSDL 1.1 for said comparison.
All my proposed language does is make what you allege is already the case
far more clearly the case. The fact that we cannot control what other interface
definitions do, and whether they define a mapping at all, seems to speak
to the folly of ostensibly requiring that they map to WSDL 1.1 in the first
place.
</eej>
<mje>
Fine, but how do you intend that this should be handled in the SCA specifications?
The wording used below in your proposal does nothing that I can see to
provide any information about the mappings to be used - it seems to be
left up to the SCA runtime to decide. I don't see how this provides
any guarantee of portability or interoperability. So why would the
SCA specifications want to leave a hole like this?
</mje>
<eej>
You seem to want it both ways - since it is outside of SCA, we don't control
it and shouldn't (and yet the current spec attempts to), and yet you expect
my proposal to define how to constrain such outside interface definitions?
I'll turn this around. What constraint do you wish to see defined on the
OASIS CSA defined interfaces (interface.wsdl, interface.java - there are
no others, right?) that my proposal discards? I could easily wrap up this
proposal if I understand that.
</eej>
-Eric.
On 2/18/11 2:32 AM, Mike Edwards wrote:
Eric,
Some comments inline as <mje>...</mje>
Yours, Mike
|
|
Dr Mike Edwards
| Mail Point 146, Hursley
Park
|
|
STSM
| Winchester, Hants SO21
2JN
|
SCA & Services
Standards
| United Kingdom
|
Co-Chair OASIS SCA
Assembly TC
|
|
|
IBM Software Group
|
|
|
Phone:
| +44-1962 818014
|
|
|
Mobile:
| +44-7802-467431 (274097)
|
|
|
e-mail:
| mike_edwards@uk.ibm.com
|
|
|
|
|
Hi Mike,
I'm confused by the particular concern related to portability.
If I've built a composite that works with vendor X, using interface.vendorXIntfA
and interface.vendorXIntfB, why would I have any expectation that I could
take said composite and move it to a different SCA runtime, and have any
expectation that it would work?
For that matter, just using interface.vendorXIntfA, and interface.vendorXIntfA,
even though SCA 1.1 defines and allows compatibility between these two
- even if they don't map to WSDL 1.1, I still wouldn't stand a chance of
moving said composite away from vendorX.
<mje>
My observation is that if you are considering things that are simply proprietary
to a single vendor, then you can do virtually as you wish - this can be
outside any standard, since standards are all about portability and interoperability.
Here you are painting a scenario which involves neither portability nor
interoperability, so why do the SCA specifications matter?
</mje>
Now, circling back to the first case, why do I need to know how vendorX
determines compatibility between interface.vendorXIntfA & interface.vendorXIntfB?
It should be up to the vendor to decide.
The key point here is that with my proposal, vendorX is not required
to determine compatibility between instances of vendorXIntfA and vendorXIntfB
by mapping to WSDL 1.1. They should be able to map to a different representation,
and ought to choose that representation based on what best preserves the
semantics. There are numerous ways in which a WSDL 1.1 mapping can drop
semantics. That is, unless you start adding all sorts of extension elements
to WSDL 1.1, at which point it just becomes yet another interface description
that happens to use WSDL 1.1 for a portion of its representation.
<mje>
I actually agree with you for the case that you have here - something purely
proprietary to one vendor. In such a case, the vendor can help themselves,
do what they please.
In such a case, the SCA specifications can be silent. There is nothing
to say.
</mje>
As for a concrete example (completely made up) that you asked for:
- interface.tibcoWSDL20 & interface.tibcoJMX
Why,
oh why would I be expected to map both of these to WSDL 1.1 in order to
determine compatibility, when I could just map the interface.tibcoJMX instance
to interface.tibcoWSDL20?
<mje>
The simple answer is: you can do as you please within TIBCO. Help
yourselves. The specs don't prevent this. There are no issues
that I can see.
Of course, I argue that it would be a good idea even for TIBCO to write
down the mapping they intend to use between tibcoWSDL20 and tibcoJMX, otherwise
the TIBCO customers might get confused. However, that is no concern
to the OASIS SCA specifications.
My concern is if ever it is expected that these different interface types
are expected to work across SCA runtimes from different vendors. In
that case there is a need to define how things are supposed to work. Please
give me an idea of what you would put into the SCA specifications to cover
this.
</mje>
Putting this in a chart:
| WSDL 1.1
| interface.java
| interface A
| interface B
|
WSDL 1.1
| directly compare
| map to either
| map to either
| map to either
|
interface.java
| map to either
| directly compare
| map to either
| map to either
|
interface A
| map to either
| map to either
| directly compare
| map to either
|
interface B
| map to either
| map to either
| map to either
| directly compare |
The above is my proposal, whereas, the next table shows how the spec currently
reads:
| WSDL 1.1
| interface.java
| interface A
| interface B
|
WSDL 1.1
| directly compare
| map to WSDL 1.1
| map to WSDL 1.1
| map to WSDL 1.1
|
interface.java
| map to WSDL 1.1
| directly compare
| map to WSDL 1.1
| map to WSDL 1.1
|
interface A
| map to WSDL 1.1
| map to WSDL 1.1
| directly compare
| map to WSDL 1.1
|
interface B
| map to WSDL 1.1
| map to WSDL 1.1
| map to WSDL 1.1
| directly compare |
The difference lies not on the diagonal, but all the options around that.
The problem is that interfaces A & B may have richer semantics than
WSDL 1.1. The existing spec'd expectation potentially forces the provider
of interface A to declare something incompatible when it isn't, or worse,
declare something compatible when it isn't, because semantics can be lost
when mapping to WSDL 1.1.
On top of all of that, it happens that there isn't actually a test you
can define that normatively verifies any of this, except the top left corner,
because SCA currently only defines interface.wsdl & interface.java.
If you want, we could further nail down that detail in my proposal.
However, I don't see any value in mandating that interface A & interface
B have to be converted to WSDL 1.1 before being compared, particularly
since we can't test that.
<mje>
Fine, but how do you intend that this should be handled in the SCA specifications?
The wording used below in your proposal does nothing that I can see to
provide any information about the mappings to be used - it seems to be
left up to the SCA runtime to decide. I don't see how this provides
any guarantee of portability or interoperability. So why would the
SCA specifications want to leave a hole like this?
</mje>
-Eric.
On 2/17/11 7:47 AM, Mike Edwards wrote:
Eric,
I'm sorry that this has been left lonely and uncommented on. We're
clearly enjoying event processing too much.
There is a comment inline. I think that it would also help if you
could describe at least one concrete example of
a mapping that you'd like us to support.
Yours, Mike
In a previous
email I proposed something similar to the following
change. This time I tried to be more precise, so that this is more
than just directional.
Change 6.2.1 #6, 6.2.2 #6, and 6.2.3 #6 in the following pattern:
Replace text that reads:
"for checking the compatibility of 2 remotable interfaces which are
in different interface languages, both are mapped to WSDL 1.1 (if not already
WSDL 1.1) and compatibility checking is done between the WSDL 1.1 mapped
interfaces.
For checking the compatibility of 2 local interfaces which are in different
interface languages, the method of checking compatibility is defined by
the specifications which define those interface types, which must define
mapping rules for the 2 interface types concerned."
... with the following ...
"The interfaces, whether local or remotable, must map onto a common
interface description language, and that the two interfaces are compared
on the basis of that common interface description language. See section
Comparing Interface Descriptions of Different Types for a discussion."
... and then add a section 6.2.4:
6.2.4 Comparing Interface Descriptions Of Different Types
A variety of interface descriptions for services exist. Examples of well-known
types include XML-RPC, CORBA, REST, WSDL 1.1, WSDL 2.0, SNMP, and JMX.
Implementations ought to use the interface type mappings that best
preserve the semantics of the underlying exchange.
To establish a basis of comparison between two different interface definition
types, the implementation has to map one or both of the interface descriptions
to a common definition type. The implementation has to identify that
common type, and ought to keep possible conversion errors to a minimum
by eliminating spurious conversions, and selecting the form with the best
semantic relevance. For example, if one interface description type
maps to WSDL 1.1, and the other interface type is WSDL 1.1, then the SCA
implementation ought to compare on the basis of WSDL 1.1. When neither
interface type can directly convert to the other interface type in question,
and conversion to WSDL 1.1 is possible, implementations SHOULD map both
interface descriptions to WSDL 1.1.
<mje>
The question is - who defines the mapping?
If I've got <interface.x.../> and <interface.y.../>, who says
what the mapping between x and y is for some actual interfaces of each
type?
Is this to be described in either or both of the specifications for x and
y - or is it simply left to the SCA runtime to pick what it pleases?
I am somewhat concerned by the potential for lack of portability here,
if runtimes are left free to choose what they will. I think the current
formulation of the SCA spec aims to get consistency between runtime implementations.
How can we ensure this for the relaxed case?
</mje>
Justifications for the above:
The specification already allows for the use of remotable interfaces defined
using something other than WSDL 1.1. For example, a Java JMX interface
description can be marked remotable. The existing rules only reject
the notion of compatibility when the two interfaces being compared are
of different types, but don't actually reject the notion of remotability
being applied to said interface types. As a possible example, XML-RPC
can be represented by a variety of description languages.
The above change relaxes a constraint that imposes on an implementation
the need to declare incompatibility where none may exist. Specifically,
by allowing additional scenarios to interoperate, the composers will be
able to express interface definitions that more closely align to their
implementation language, and the semantics of the underlying problem, rather
than by restricting themselves to the subset of the interface description
that maps to WSDL 1.1.
Unless stated otherwise above:
IBM United Kingdom Limited - Registered in England and Wales with number
741598.
Registered office: PO Box 41, North Harbour, Portsmouth, Hampshire PO6
3AU
Unless stated otherwise above:
IBM United Kingdom Limited - Registered in England and Wales with number
741598.
Registered office: PO Box 41, North Harbour, Portsmouth, Hampshire PO6
3AU
Unless stated otherwise above:
IBM United Kingdom Limited - Registered in England and Wales with number
741598.
Registered office: PO Box 41, North Harbour, Portsmouth, Hampshire PO6
3AU
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