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Subject: RE: [soa-rm-ra] Please re-read Sect 4.3.4 of soa-ra-cd-02
Jeff, A useful analogy that comes to
mind is when we built an addition on our house. We hired an architect and
a general contractor, and the general contractor was responsible for hiring plumbers,
carpenters, carpet installers, etc. The general contractor had the role
of the composite service. I sometimes saw the plumber when plumbing work
was being done (often didn’t) but didn’t usually know the details
of what the plumber was doing or when. (The general contractor did
mention at some point that the plumber was two days late and there would be
some workarounds.) Same for the other subcontractors. I knew there
were dependencies but I knew nothing of the details and assumed these would be
handled adequately by the general contractor as part of his service. If
there were independent policies on the part of the subcontractors, I was
unaware of these and only dealt with the policies of the general
contractor. For example, there was a payment schedule and I assume the
general contractor took into account the need to pay the subcontractors, but I
only dealt with the policies as specified by the general contractor (my
composite service). I look at the provider of a
composite service as the consumer of all its components, and the general
contractor dealing with each of his subcontractors is no different in general
from me dealing with him. Also, the general contractor coordinating among
the subcontractors was similar to me coordinating with the general contractor
and the architect. One place where I may not
understand your perspective and have trouble relating to my home addition
example is lines 2338-2346 when you talk about a Service Management
Service. You say this service needs visibility into the composition so it
can manage dependencies, but I see managing dependencies as the job of the
composite service. Now the composite service may make use of tools to
monitor the components (or the ecosystem, in general) and may make use of
operation research tools to balance complex tradeoffs among requirements.
However, these are tools (possibly services) used by the composite to manage
its requirements and dependencies. I do not think of there being some
independent management entity unless the full management function was
subcontracted by the composite. Quick other points: -
Description information
is never complete but various subsets of “complete” description
should contain consistent information -
A given service may
have more than one endpoint but I would expect a single information model and, possibly,
a single process model. Imagine the difficulty in writing a clear, machine-processible
description if this is not the case. -
No service operates
in a vacuum, and trying to convince people that anything infrastructure is not
a service will be a very hard sell. Enough for now. Ken --------------------------------------------------------------------------- Dr. Kenneth Laskey MITRE Corporation, M/S
H305
phone: 703-983-7934 7515 Colshire
Drive
fax: 703-983-1379 McLean VA 22102-7508 From: Estefan, Jeff A (3100)
[mailto:jeffrey.a.estefan@jpl.nasa.gov] RAF Colleagues, A very interesting discussion
ensured today on the topic of atomic vs composite services. I’d
like to encourage everybody who participated in the discussion to re-read Sect
4.3.4 in its entirety prior to next week’s meeting and proposed (via
e-mail in the interim if you like) some wording changes to the formal
definitions captured in this section. The reference document is
soa-ra-cd-02 lines 2311 to 2350. Remember that the original issue
resolved around multiplicity of interfaces and descriptions and we did not even
discuss that point today and for the atomic service case, the issue around the
language of interacting with other services (which is accepted to change to use
or rely on other services). Indeed the importance of this
distinction depends on one’s perspective but I ask that you imagine the
challenges from a management point of view for a highly composed service in
terms of management of policies and contracts of each of the services that make
up the composite service. I think this has some real practical
implications and they are not trivial. Thanks! - Jeff |
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