Title: Re: [soa-rm-ra] Questions on action model
Duane wrote: "In an ecosystem of services,
there could potentially be many service
descriptions for a service. The
service description a consumer uses may be dependent on the entity the consumer interacts with when
they use the service, or it could be
dependent on the particular context the
service description is provided.
Because of unforeseen possibilities for a
service to have multiple service descriptions, I do not think the OASIS SOA RA can qualify one
service to one service
description."
I have a lot
of concerns about underlined statements.
1) Service
description gets used as the service definition now. I agree that in an
ecosystem not all information about the service is in the Service Descriptor.
However, in this case, I prefer to recognise that I have different 'domains' in
the ecosystem of services (voice, signs, UDDI, etc.) where the Service
Description is the single unique one.
2) To me,
the "service description a consumer uses may be dependent on the entity the consumer interacts with when
they use the service" looks much
more like an execution context and related Service Contract than a service
description. Again, "be dependent on the
particular context the service description is provided" is either services ecosystem domain
specific Description or the EC and Service
Contract.
3) as I mentioned
before, SOA RM states that EC is not a context of service interaction only (
though in many places it says so ) but also the context of service execution per
se. If we allow "a service to have
multiple service descriptions" (w/o defining concrete conditions where it is
possible), we have to clearly distinguish it from a service to have multiple service descriptions
in multiple service execution contexts - interaction and execution
ones.
4) I, personally,
dislike the idea of "a service to have
multiple service descriptions", at least, in the same Service Description
Repository. Though this is a lower level technical implementation detail,
it is VERY important for practical use of SOA and quoted statement above can
easily screw it, which I hate.
-
Michael
Important: Fidelity Investments International
(Reg. No.1448245), Fidelity Investment Services Limited (Reg. No. 2016555),
Fidelity Pensions Management (Reg. No. 2015142) and Financial Administration
Services Limited (Reg. No. 1629709, a Fidelity Group company) are all registered
in England and Wales, are authorised and regulated in the UK by the Financial
Services Authority and have their registered offices at Oakhill House, 130
Tonbridge Road, Hildenborough, Tonbridge, Kent TN11 9DZ. Tel 01732 361144.
Fidelity only gives information on products and does not give investment advice
to private clients based on individual circumstances. Any comments or statements
made are not necessarily those of Fidelity. The information transmitted is
intended only for the person or entity to which it is addressed and may contain
confidential and/or privileged material. If you received this in error, please
contact the sender and delete the material from any computer. All e-mails sent
from or to Fidelity may be subject to our monitoring procedures. Direct link to
Fidelity’s website - http://www.fidelity-international.com/world/index.html
From: Duane Nickull
[mailto:]
Sent: 12 October 2007
16:49
To: Ken Laskey; Scott Came
Cc:
Subject: Re: [soa-rm-ra] Questions on
action model
Concur. Look at the cardinality of WSDL. Not
everything is mandatory either. On a purely logical level, consumers can
use only that which they require. It is unlikley that any one service
description artifact would in fact contain *all* the information
required.
At least some info is known via alternative mechanisms
(voice, signs, UDDI, etc.)
Duane
On 10/11/07 6:22 PM, "Ken
Laskey" <> wrote:
The RM says
The service description represents
the information needed in order to use a service. In most cases, there is no
one “right” description but rather the elements of description required
depend on the context and the needs of the parties using the associated
entity.
Thus, the implication is there may be overlapping descriptions
relevant to different contexts.
Ken
On Oct 11, 2007, at 8:08
PM, Scott Came wrote:
Danny:
I don't personally have a strong feeling
one way or the other on this
issue. I did sense the "one
description" position as the subcommittee
consensus, however...mostly
from reading the RA 0.2 draft.
Thanks.
--Scott
-----Original
Message-----
From: Danny Thornton [mailto:]
Sent:
Thursday, October 11, 2007 3:55 PM
To: Scott Came;
Subject: RE: [soa-rm-ra] Questions on
action model
Scott,
Thank you for the summarization.
The only statement I
have an exception with is 3, A service has
one
description.
In an ecosystem of services, there could
potentially
be many service descriptions for a service.
The
service description a consumer uses may be dependent
on the
entity the consumer interacts with when they
use the service, or it
could be dependent on the
particular context the service description
is
provided. Because of unforeseen possibilities for a
service
to have multiple service descriptions, I do
not think the OASIS SOA RA
can qualify one service to
one service
description.
Danny
--- Scott Came
<> wrote:
Subcommittee:
I'd like to take
attempt a summarization of this
thread. Note the
word
"attempt"...please let me know if I've misconstrued
anything
said so
far.
1. The action model of a service may
contain
multiple actions
2. The actions in a given service's
action model may
produce
distinct real-world effects, meaning that
a consumer
may choose to
interact with (invoke?) some subset of
actions and
not others
3. A service has one description, but that
one
description may make
specific reference to particular actions
in order to
describe their
individual effects, and it also may
specify specific
policies for
individual actions, though those
specific individual
policies can be
viewed as part of one whole
policy for the service.
4. The process model of a service shows how
a
consumer may interact
with (invoke?) specific actions in
sequence to
accomplish some business
function aligned with the
service's RWE
5. There may be multiple processes in the
process
model, involving
different sequences and different
functions
6. A consumer may interact with (invoke?) a
single
action to
achieve a particular effect (whether that is
a
process with one step, or
no process, is an issue I
suppose)
7. The mechanism by which a consumer interacts with
a
service is by
invoking an action through message exchange;
that
is, the consumer and
service exchange information (in the
form of a
message) to achieve some
effect
8. Interaction with
different actions can be by
different MEPs
9. The decision about
service boundaries-which of
all possible
actions should be in a
given service's action
model-can be productively
guided by a set
of design principles, which the RA
may include at some
future
time. Principles should be carefully and
precisely
defined.
The example again is an Employee Time
Management
service. The action
model of this service might
consist of four actions:
add time records,
update existing
time records, delete time records,
and view time
records. A
process model for this service may, for
example, indicate
that it
makes sense to view time records prior to
updating them.
But,
it is also possible to add time records
in
isolation...without any of
the other actions being
involved. The overall RWE
of this service is
management of
employee time, but each action has a
separate effect
of
independent value to a consumer. There is no
absolute
rule regarding
whether it makes sense to include all four of
these
actions in one
service-without more analysis, it is not
clear
whether this is a "good"
service model or not.
However, there are some
design principles that an
architect
(creator of a concrete architecture) can
apply in making
this
determination: loose coupling, statelessness,
autonomy,
abstraction,
etc.
Thanks.
--Scott
________________________________
From:
Ken Laskey [mailto:]
Sent:
Thursday, October 11, 2007 11:09 AM
To: Scott Came
Cc:
Subject: Re: [soa-rm-ra] Questions on
action model
Scott,
Indeed I do not expect
we (and anyone else) will
provide a definitive
cookbook for
defining services. However, it is
exactly those
guiding
principles that I think will be valuable and with
which
the RA should be
consistent. Thomas Erl's book may provide a
good
starting point. If
anyone can summarize between now and
when I
eventually make it to a book
store (or log into Amazon), we
can begin considering
those.
Note when we mention
principles, we have to do much
more than use terms
which are
familiar but overused and never really
defined. The
RM
specifically took shots at loose-coupling
and
coarse-grained. I also
put agility into that
category. When we state the
principles (assuming
we can),
those SHOULD be phrases that convey enough
meaning that
they
cannot be automatically misconstrued (by accident or
on
purpose) and
then crisply elaborated.
Again, I'm
energized to revise the service
description model but have a
long
list of household chores to catch up on first.
Keep sending
ideas.
Alternately, you can come over and fix the
lawn
mower.
Ken
On Oct 11, 2007, at
1:35 PM, Scott Came
wrote:
Ken:
Regarding your
#1...
I think this kind of specific guidance is
best
reflected in a set of
principles. I don't believe there
will be a "one
size fits all" set of
rules that tell you, in every
situation, how to
design a service
properly. The best you
can do is identify the
principal forces at
play-those factors
that, at a minimum, the designer
should at least
consider when
setting service boundaries. Those
forces are represented
in
principles that say what should characterize a
proper
service.
Proper application of these principles (selecting
among
the sometimes
competing forces) requires the skill of a
designer,
but well-stated
principles accelerate the design process
and bound
the designer's
discretion somewhat, in pursuit of an
overall design
objective.
And not just any old set of
principles will do. SOA
has an overall
purpose-to increase
agility, adaptiveness,
responsiveness to
change-so
=== message
truncated
===
________________________________________________________________________
____________
Boardwalk
for $500? In 2007? Ha! Play Monopoly Here and Now (it's
updated for
today's economy) at Yahoo! Games.
http://get.games.yahoo.com/proddesc?gamekey=monopolyherenow
-----------------------------------------------------------------------------
Ken
Laskey
MITRE Corporation, M/S H305 phone:
703-983-7934
7151 Colshire Drive
fax:
703-983-1379
McLean VA
22102-7508
--
**********************************************************************
"Speaking
only for myself"
Blog - http://technoracle.blogspot.com
Community
Music - http://www.mix2r.com
My Band -
http://www.myspace.com/22ndcentury
MAX
2007 - http://technoracle.blogspot.com/2007/07/adobe-max-2007.html
**********************************************************************
