Simon,
You're perfectly entitled (as is anyone
else) to take the view that a new issue is not valid for
any reason. That's the thinking
behind the process whereby anyone can raise an issue but
it has to go through a vote before it
gets opened.
Anyhow, to the merits of the current
issue...
let me try to provide some motivation
for the issue, even though I'm not the raiser of the original
issue, but I do see the thinking behind
it.
One of the ideas within SCA is the simplification
of the assembly task - simplifying the connection
of some reference to some service. Binding.sca
is one of the tools used to bring simplification.
It basically says "look, I want
to connect THIS to THAT and I don't particularly care how it is done
- just make the connection and satisfy
any intents I've specified"
Dave Booz has always taken the view
(which I agree with) that this is the 80% case when doing
Assembly. Only when you're really
dealing with the "outside world" is there a strong need to
get into concrete bindings and the associated
specialized endpoint addresses and other
paraphernalia.
Now there are cases where you can end
up with mixtures of bindings. So, we may have at the
domain level a component A with service
S1 that needs to be available externally over the
Web Services binding. So S1 is
configured that way. Along comes component B with
reference R1 - and the assembler decides
to connect that reference to S1 as well.
Currently, for R1, we would have to
configure it with a Web Services binding, with an endpoint
URL pointing to the web service endpoint
of A/S1. This is a lot more complex than simply
stating @target="A/S1" on
R1. It is also harder to parse after the fact.
So, that's the real world case, I think.
The argument is being made that it is a great simplification
for the Assembler NOT to have to go
deal with the complexities of the web service binding.
Stating binding.sca and the SCA target
address should be enough. The SCA runtime can
work out the rest - yes, it would probably
use web services under the covers (at least, if the
components lived on different machines).
Another way of stating this might be
to say "binding.sca is ALWAYS present", except that makes
me uncomfortable for the cases where
intents are used to force the use of particular bindings
where the component code is written
using binding-specific APIs. I prefer to go along with the
idea that it is possible for binding.sca
to be "coerced" to the binding of the other end of the wire.
So, I think the issue is based on:
a) current spec is more complex than
it needs to be
b) there is a simpler apporach for the
assembler - and the proposal states it
Yours, Mike.
Strategist - Emerging Technologies, SCA & SDO.
Co Chair OASIS SCA Assembly TC.
IBM Hursley Park, Mail Point 146, Winchester, SO21 2JN, Great Britain.
Phone & FAX: +44-1962-818014 Mobile: +44-7802-467431
Email:
Simon Nash/UK/IBM@IBMGB
28/11/2007 08:35
To
"OASIS Assembly" <>
cc
Subject
Re: [sca-assembly] [NEW ISSUE] Wiring
from a reference with no binding to a service with a binding
This issue raises a general point about what justification
is needed in
order to open an issue.
In general an issue should say that something is wrong and describe what
the problem is. It may also give a proposal for a change to resolve
the
problem. The "something is wrong" could be an error or
inconsistency in
the spec, or it could be a real world use case that the spec does not
address adequately. I don't think an issue should be raised based
on an
opinion that says "I don't like spec rule X and I prefer rule Y instead."
With this issue I don't see any clear description of what is wrong with
the current spec rules. The spec appears to be clear and consistent
as it
stands. All I see is an assertion that the rule in the current spec
imposes an "unreasonable requirement".
Why is this spec rule unreasonable? What real world use case has
a
problem because of this rule? IMO the rule is fine as it stands,
and no
change is needed. However, I'm prepared to be educated on this, and
if
the rule is causing a problem, then we we should look at the problem and
see what spec change needs to be made to resolve the problem. The
solution could be the one proposed, or there could be a different
solution. Without a clear problem statement and use case to drive
the
discussion, the debate will come down to one person's technical opinion
against another's, which is unlikely to be productive.
Simon
Simon C. Nash, IBM Distinguished Engineer
Member of the IBM Academy of Technology
Tel. +44-1962-815156 Fax +44-1962-818999
Mike Edwards/UK/IBM@IBMGB
27/11/2007 15:42
To
"OASIS Assembly" <>
cc
Subject
[sca-assembly] [NEW ISSUE] Wiring from a reference with no binding to a
service with a binding
<This issue is transferred from the SCA Policy TC where it was dubbed
POLICY-34>
RAISER Michael Rowley (original)
TARGET: SCA Assembly Specification
DESCRIPTION:
The algorithm in the policy spec says that it is _not_ possible to wire
from a reference that does not declare a binding (i.e. uses binding.sca)
to a service that declares one or more bindings. However, I think this
should be possible.
It is an unreasonable requirement to say that a service with a binding
can
only be the target of a reference that has that same binding. The default
binding (binding.sca) should be treated as the "I don't care"
binding, and
should work with any binding available within the domain. Or, more
precisely, any binding that can satisfy the required intents.
Section 4.8.1 of the Policy frmework spec states:
The wiring compatibility algorithm below determines the compatibility of
a
wire by a pairwise choice of a binding instance and the corresponding
policySets on each side of the wire.
This should be changed to the following:
If either side of a wire does not specify a binding (or explicitly
specifies binding.sca) the wire is considered to be valid for the purposes
of policy processing. If both sides of the wire use binding.sca then the
policies will be determined by the union of the required intents of both
sides (policy sets aren't used with binding.sca). Otherwise, the bindings
and policies used for the wire will be determined by adding the intents
that are required by the binding.sca end of the wire to the other end of
the wire and then following the section 4.10 algorithm in the Polcy
Framework.
If neither side of the wire uses binding.sca, then the wiring compatibilty
algorithm below is used for determining compatibility. Note that there
may
be many binding instances present at each side of the wire. This algorithm
determines the compatibility of a wire by a pairwise choice of a binding
instance and the corresponding policySets on each side of the wire.
PROPOSAL:
The following should be added to the Wires section of the Assembly
specification:
If either end of a wire does not specify a binding (or explicitly
specifies binding.sca) the wire is regarded as valid. In other words,
binding.sca is regarded as being compatible with
any other type of binding. Where other types of binding are applied
to
each end of a wire, compatibility of the two bindings is determined by
the
specifications for the two bindings
involved, allied to the intent and policies attached at each end. In
general, a wire which has two different binding types at each end (non
binding.sca) is likely not to be valid.
If both ends of the wire use binding.sca then the policies will be
determined by the union of the required intents of both ends (policy sets
aren't used with binding.sca).
Otherwise, where one end of the wire uses binding.sca, the bindings and
policies used for the wire will be determined by adding the intents that
are required by the binding.sca end of the wire to the other end of the
wire and then following the algorithm defined in the Policy Framework
specification section 4.10.
If neither end of the wire uses binding.sca, then the wiring compatibilty
algorithm described in section 4.10 of the Policy Framework specification
is used for determining compatibility. Note that there may be many binding
instances present at each side of the wire. This algorithm determines the
compatibility of a wire by a pairwise choice of a binding instance and
the
corresponding policySets on each side of the wire.
Yours, Mike.
Strategist - Emerging Technologies, SCA & SDO.
Co Chair OASIS SCA Assembly TC.
IBM Hursley Park, Mail Point 146, Winchester, SO21 2JN, Great Britain.
Phone & FAX: +44-1962-818014 Mobile: +44-7802-467431
Email:
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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