| So,how do we respond to this?
The wiki may help on this but I think one of the topics at the editors' mtg may be how to glean key thoughts from an overactive email list, using the service definition as a first challenge.
Ken Begin forwarded message: Date: August 10, 2005 3:50:32 PM EDT Subject: Re: [soa-rm] Definition(s) of "service"
Ken:
Thank you for owning this! Good luck next week.
May I suggest that the Editors use the WIKI page during their meeting?
Duane
Ken Laskey wrote:
Duane,
I hate to say this (and my fellow co-editors may disagree) but I think the task needs to be taken on by the editing team as a whole. My SOA mailbox has over 2300 messages with many threads having a bearing on this, and even a cursory scan will be a significant effort. Also, as the current designated editor for the service section, I don't see a good way of just dumping it onto someone else.
I would be willing to be talked out of this position.
Ken
At 12:25 PM 8/9/2005, Duane Nickull wrote:
I would like to request a volunteer or volunteers to own this issue and ensure that none of the depth of this conversation is lost. We have passed around heaps of good thoughts. The owner would essentially be responsible for capturing the views / opposing views and keeping documentation up to date as this gets discussed. The owner would not be entitled to simply gloss over with their own point of view but would act much like an editor - reflecting the consensus or the TC or noting the lack thereof.
Anyone interested in owning this? Duane
Frank McCabe wrote:
I strongly resist the tendency of equating service with the 'back end capability' (or whatever). This is a dangerous and non-scalable direction to go in:
1. The implementation of a service is none of the service consumer's business. 2. The service consumer should not even be able to figure out how a service is delivered. If it can, then you will get security risks and/ or scalability issues 3. A given capability may not be fully exposed in a given service 4. A given service provider agent may not *have* the capability offered in its service -- it may know someone who knows ... it may not be possible to characterize the capabilities of a service provider. 5. From the point of view of the service consumer, fundamentally, it cannot (normally) distinguish the surface aspects of interacting with a service and the deeper aspects that rely on the service's realization (e.g. this is an Oracle database so be careful with your SQL)
On the other hand, the service consumer interacts with a service in order to achieve an effect. In most interesting cases this is a 'real- world effect'. The consumer is interested in the fact that the bank account has been credited.
Interestingly, these real world effects can *also* be expressed in public semantic terms -- without relying on representing the internal state of the resource. For example, a bank customer wants to know that his or her account has a certain balance. This is a fact that is warranted by the bank; not simply by the database resource that the bank happened to use to store the account information. I.e., there is a public 'on-the-wire' assertion that the bank attests whenever a authorized request (again, note the on-the-wire nature of this) is made to the appropriate bank service.
Frank
On Aug 8, 2005, at 3:02 PM, Chiusano Joseph wrote:
-----Original Message----- Sent: Monday, August 08, 2005 5:50 PM Subject: RE: [soa-rm] Definition(s) of "service"
As appeared earlier in this thread, there are contexts in which it is not necessary to discriminate between the capability and the service that accesses it,
Ken, are you equating capability with resource? I recall a reference to resource that fits the above description, but not one to capability.
Joe
Joseph Chiusano Booz Allen Hamilton O: 703-902-6923 C: 202-251-0731
and our discussion of service can make this clear. However, I think this thread has also shown ample examples of where the service and the capability are clearly separate concepts and where it may be useful to allow that difference to be captured. For example, it is likely for someone to ask if two services are the same. While we do not address that particular question, it is far simpler to handle if we know whether the underlying capability is the same than if we obscure that difference at first principles.
Ken
At 05:03 PM 8/8/2005, Chiusano Joseph wrote:
-----Original Message----- Sent: Monday, August 08, 2005 12:10 PM To: Ken Laskey Subject: Re: [soa-rm] Definition(s) of "service"
This is going in a weird direction. I believed that there was significant consensus that the
notion of
service that we are interested in *is* the interface/boundary/offering.
The capability behind the service -- that which makes the service possible -- is private and out of bounds. That capability
is, by the
way, best described using agent terminology.
Respectful non-concur. IMHO, the service *is* the
capability, and the
service *has* an interface through which interaction with that capability may be possible.
Joe
Joseph Chiusano Booz Allen Hamilton O: 703-902-6923 C: 202-251-0731
Frank
On Aug 8, 2005, at 8:50 AM, Ken Laskey wrote:
This is good because it highlights the bits of
confusion we have
to explain our way around.
The user interface is the facade through which the user
interacts with
a service (i.e. inputting information/requests, viewing results) but there may be delivery capabilities that
are invoked
through relevant services and the delivery capabilities are the mechanisms through which results are packaged and sent to the requester/consumer. For example, if I make a request for
an image and
as part of that request, information about my connectivity is provided, logic (capability) can be executed (possibly
invoked through
a service) to decide which delivery mechanism is most
appropriate
(e.g. high res or low res, what kind of compression, ...).
Ken
At 11:18 AM 8/8/2005, Michael Stiefel wrote:
Actually, I think two things are being confused here.
There is one service being used by several different
applications.
The user interface (i.e. the actually delivery mechanism)
is not part
of the service, or strictly speaking part of the SOA.
Michael
At 10:43 AM 8/8/2005, Ken Laskey wrote:
I'd have to think about this further but in general I
would say yes.
The underlying capability is making pizza and offering
the product
for sale. The mechanisms for accessing the capability are in person, by phone, online. Note, the capability existed
before there
was online ordering and this is just another
mechanism to access
a capability that already existed. Interestingly from an orchestration/choreography sense,
the delivery
of the pizza (in person pickup, delivery service from
pizza place,
third-party delivery (e.g. Takeout Taxi around here)) constitutes another set of capabilities that can
have service
interfaces and can be combined in response to invoking
the ordering
service. All of these can be used for delivery of things
other than
pizza (even the pizza place might also deliver sandwiches).
I think part of the confusion is that a *physical*
delivery service
is a millennia-old, longstanding capability that has
nothing to do
with SOA and is *not* the service in the SOA sense
but it uses a
different aspect of the S word.
Ken
Does this imply that if I order a pizza online vs. order a pizza over the phone vs. order a pizza by walking into the store, that these are all separate services?
--JJP
-----Original Message----- Sent: Thursday, August 04, 2005 12:35 PM Subject: RE: [soa-rm] Definition(s) of "service"
This gets back to the previous discussion when we
talked about
resources, i.e to what extent the service is the
mechanism to
access (possibly coordinate) capability vs. when is it
considered
the capability itself.
I think any consideration of the service as the
capability/resource
should be very limited.
Ken
At 11:07 AM 8/4/2005, Chiusano Joseph wrote:
-----Original Message----- Sent: Thursday, August 04, 2005 11:04 AM Subject: RE: [soa-rm] Definition(s) of "service"
Somehow saying service *provides* capabilities
misses the SOA
motivation to provide an effective way to bring together the
parts I
need to solve a problem. Integration is often
of disparate
parts
that exist for their own purposes. Service can help
coordinate but
the challenge is to make use of the tools/resources/
capabilities
that already exist, not to create new stovepipes.
Saying the
service provides all this is a tempting
simplification but
I
fear it
will trivialize the concepts most in need of
clarification.
Agree - and I should clarify that I was merely saying that a
service
provides capabilities (in general). Combining a
capability here, a
capability there, here a capability, there a capability,
everywhere a
capability (oops sorry - that's the EIEIO song), we
have composite
capabilities.
Joe
Joseph Chiusano Booz Allen Hamilton O: 703-902-6923 C: 202-251-0731
Ken
At 10:35 AM 8/4/2005, Chiusano Joseph wrote:
-----Original Message----- Sent: Thursday, August 04, 2005 10:18 AM Subject: RE: [soa-rm] Definition(s) of "service"
I'd still like to emphasize service as the access to capabilities for which there are extra-service
motivations for
their existence and requirements for use of the
capabilities
that must be
navigated
by the service. Thus,
"A service is a mechanism to enable access
to a set of
capabilities,
I would say that access control mechanisms enable such
access, and that
the service *provides* the capabilities. Note: Use of
"access control"
is too concrete for our RM - I stated it only to illustrate
the point.
Joe
Joseph Chiusano Booz Allen Hamilton O: 703-902-6923 C: 202-251-0731
where the access is provided using a prescribed
interface and is
exercised consistent with constraints and policies as
specified by
the service description."
Ken
Just trying to sort through this; some common themes
that seem to
be acceptable:
A service provides capabilities. A service is accessible. (If this is true, then service
cannot be a
verb.) A service has an interface. (If this is true,
then a
service has
a boundary.) A service interface is
prescribed. (Then
a
service and its
interface are distinct, and the interface has
associated rules.
I'm not sure this is true, the interface may
describe the
rules,
but Im not
sure it has rules. In fact, I'm inclined to
suggest that
the interface
defines the rules for accessing the service. Which
would lead me
to suggest that the service interface is more than a
specification of the
data model, but also of the policies
associated with
the
service.)
A service is a set of behaviors. (Not sure I'm on board
with this,
something about behaviors doesn't sit well.)
Given this, perhaps something like:
"A service is a bounded set of capabilities that are
accessible through
a prescribed interface."
-- JJP
P.S. I think this definition might just be
flexible enough
to navigate
the service offer/contract discussion also.
-----Original Message----- Sent: Thursday, July 28, 2005 12:32 PM To: Frank McCabe; SOA-RM Subject: RE: [soa-rm] Definition(s) of "service"
Frank,
While I believe that the previously proposed
definition is
sufficient,
I offer the following as a compromise.
Hopefully, the
notion of
"capabilities" addresses your issue of
needing to get
things done.
"A service is a set of behaviors to provide capabilities
accessible via
a prescribed interface."
Ron
-----Original Message----- From: Frank McCabe Sent: Thursday, July 28, 2005 10:10 AM To: SOA-RM Subject: Re: [soa-rm] Definition(s) of "service"
I hesitate to spoil this party ... but I'm
going to :)
1. There is a distinction between action and result.
(Just ask any
roboticist) Behaviour sounds a child
misbehaving with no
discernible effect. Computer Scientists have a tendency
to focus on
the purely technical aspects of their work: bytes
shuffling around
at random within hopefully enormous memories. 2. Also, we have to bear in mind that nobody invests
millions of $s (or
even 100's of them) in systems that
contemplate their
navels
or have no
business payoff. I think that we have to directly
address the
reason that services are deployed. 3. One of the
movitating
best practice aspects of SOAs is
that clarity
and 'separation' between the providers of
services and the
consumers of
services leads to more scalable and robust
architectures.
All of the above is fuzzy language; but, at the
same time,
"A service
is a set of behaviors accessible via a prescribed
interface."
sounds a lot like bureauspeak.
I believe that there is strong consensus on the
following
characteristics: a. The concept of service is 'at the
boundary' between
service
providers and consumers. b. The service is
'there' to get
things done; but doesn't
itself denote
the engine that performs the tasks. c. There is a reason for using a service. d. There is a lot of extra metalogical information about
services that
make it possible for third parties to
develop partners
for services.
I, for one, would prefer a strongly anglo-saxon
phrasing of the
definition of service that speaks to these points.
Frank ti
--
--------------------------------------------------------------
------------------- / Ken Laskey \ | MITRE Corporation, M/S H305 phone:
703-983-7934 |
| 7515 Colshire Drive fax: 703-983-1379 | \ McLean VA 22102-7508 /
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--------------------
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--------------------------------------------------------------
------------------- / Ken Laskey \ | MITRE Corporation, M/S H305 phone:
703-983-7934 |
| 7515 Colshire Drive fax: 703-983-1379 | \ McLean VA 22102-7508 /
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--------------------
--
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-------------- / Ken Laskey
\ | MITRE Corporation, M/S H305 phone:
703-983-7934 |
| 7515 Colshire Drive fax: 703-983-1379 | \ McLean VA 22102-7508 /
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\ | MITRE Corporation, M/S H305 phone: 703-983-7934 | | 7515 Colshire Drive fax: 703-983-1379 | \ McLean VA 22102-7508 /
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\ | MITRE Corporation, M/S H305 phone: 703-983-7934 | | 7515 Colshire Drive fax: 703-983-1379 | \ McLean VA 22102-7508 /
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-- --------------------------------------------------------------------------------- / Ken Laskey \ | MITRE Corporation, M/S H305 phone: 703-983-7934 | | 7515 Colshire Drive fax: 703-983-1379 | \ McLean VA 22102-7508 / ----------------------------------------------------------------------------------
Ken Laskey MITRE Corporation, M/S H305 phone: 703-983-7934 7515 Colshire Drive fax: 703-983-1379 McLean VA 22102-7508
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