Since such a component does
not have to even be a bus configuration (there are other possible
configurations, such as a star), I think "infrastructure communications
component" (or similar) may be more abstract than using the term
"bus".
Joe
Kind Regards,
Joseph Chiusano
Booz Allen Hamilton
Visit
us online@ http://www.boozallen.com
From: Christopher Bashioum
[mailto:]
Sent: Mon 4/11/2005 11:14
AM
To: 'Ken Laskey'; 'Hamid Ben Malek'
Cc: 'Smith, Martin';
Subject: RE: [soa-rm] Architectural Scope
of Reference Model
Ken,
i don't have any problem staying away from the term
ESB. However, in light of one of your other messages (which I agree
with very much) that we capture the idea and then figure out what to call that
idea later, I would suggest that the idea of some kind of a communications "bus"
is inherent in an SOA. In other words, services
should plug into something to be a service in an SOA. The
bus defines the boundaries of the SOA. If you are on the bus,
you are "in", if you are not on the bus, you are "out". This
may be crossing into the concrete too much, but I think the RM should
probably reference something that is an abstract of a bus.
From: Ken Laskey [mailto:]
Sent: Sunday, April 10, 2005 4:29 PM
To: Hamid Ben
Malek
Cc: Smith, Martin;
Subject: Re: [soa-rm] Architectural
Scope of Reference Model
I would strongly suggest we stay away from the term ESB. It has
become an ill-defined product offering from many vendors and it is not at all
clear what needs to be present in such a component. An ESB (or some vendor's
notion of an ESB) could be an implementation mechanism but such a
conglomeration is show be the output of design, not the conceptual
reference.
Ken
On Apr 4, 2005, at 7:03 PM, Hamid Ben Malek
wrote:
[Vikas]: However the point that is lost in this discussion is
the one the original email author made i.e. we need to have an architectural
element which discusses the “communication infrastructure” in a
SOA-RM.
[Hamid] Viaks, I agree with your last sentence
above. What you call “communication infrastructure” in your above sentence,
I call it ESB. Some people misunderstand the term ESB when they look at it
literally: the word “bus” suggests to them many connotations that does not
necessary exist in an ESB. The term ESB should be understood in an abstract
way. It is a technical term that should not be analyzed through the words
that makes it.
Martin,
ESB is not exactly legacy
adapter. It is true that most implementations of an ESB incorporate data
transformations and ESBs are used mostly for EAI. However, this is only the
current implementation of the concept of ESB. Independently of the way an
ESB may be implemented, the fact still remains that there are profound
concepts in the term ESB. Concerning the peer-to-peer topology, that could
be possible with an ESB, but to assume that every transaction or call is
peer-to-peer would be a very restrictive design of what SOA is about. For
example, a client application that is connected to an ESB should be possible
to invoke a service that it does not even know about. The ESB finds the
right service, based on various criteria (that could also include the fees
to pay for invoking such a service), and the bus (ESB) makes the call on
behalf of the application. Or sometimes, the service invocation itself may
involve multiple invocations among a group of other services, orchestrated
by some important components within the
ESB.
Hamid.
From:
Smith, Martin [mailto:]
Sent: Monday, April
04, 2005 2:44 PM
To: Hamid Ben Malek
Cc:
Subject: RE: [soa-rm] Architectural
Scope of Reference Model
Hamid -
-
OK, this brings me out of my cave . .
.
What I hear people call an ESB seems to be a “legacy
adapter” (EAI - - protocol and data transform) plus various other functions
I would model as independent components, including BPM, reliable messaging,
and services location.
I think it’s essential to
separate out the “legacy adapter” functionality from the rest. And I
would prefer to model the separate functions as separate entities/whatevers
in our RM. The fact that the functions are marketed in various
combinations should not overly influence our analytical
decisions.
I’m very concerned that the use of the term
ESB suggests that every transaction in the system (meaning the relevant
collection of services and consumers) passes through the “bus.”
This seems very wrong to me.
The unifying
element in an SOA environment is the services catalog, which allows any
consumer or service to find and bind to others. After that, it’s
peer-to-peer unless “helper” or QOS services are
needed.
Whew - - I feel
better.
Martin
-----Original
Message-----
From: Hamid Ben Malek
[mailto:]
Sent: Monday, April 04, 2005 2:58
PM
To: ; 'Duane Nickull'; 'Schuldt, Ron
L'
Cc: 'Thomas Erl';
Subject: RE: [soa-rm] Architectural
Scope of Reference Model
Hi all,
I
have not been following the discussion on this mailing list as I have not
read all the messages yet (or should I say I have read only two or three
emails). But it just happened that I have read this one, and I felt
compelled to give my input to it. What Duane is calling “binding mechanism”
(namely the component(s) responsible for receiving/sending and handling of
messages) is actually part of a system called “Enterprise Service Bus”. SOA
Reference Model should try to define the general principles of an ESB in a
way that is independent of any specific implementation of the ESB. The
question whether a given service by itself is an SOA service, does not make
lot of sense. Any service could become an SOA service if it is hooked up to
an ESB. The real questions are how to define an ESB in an abstract way, and
how to define the adapters that can hook up a given service to an ESB? The
best analogy would be to compare the ESB to the internet, a service to a
computer, and the adapters to the network cable and its accessories that
allow a given computer to hookup to the internet (to get connected). In
regards to the feasibility of defining a “ping” specification to SOA-test a
service, I think that is possible, but it will be defined within the
specification of an
ESB.
Hamid.
-----Original
Message-----
From: Vikas Deolaliker
[mailto:]
Sent: Monday, April 04, 2005
11:27 AM
To: 'Duane Nickull'; 'Schuldt, Ron L'
Cc:
'Thomas Erl';
Subject: RE: [soa-rm]
Architectural Scope of Reference
Model
The
binding mechanism is transport related and IMHO would not
completely
specify the communication mechanisms need for
SOA-RM. We would still need to
have some "Hello Packets or
Ping" type specification which allows us to
answer the
question "Is that service
SOA?"
Vikas
-----Original
Message-----
From: Duane Nickull
[mailto:]
Sent: Wednesday, March 30, 2005
4:21 PM
To: Schuldt, Ron L
Cc: Thomas Erl;
Subject: Re: [soa-rm]
Architectural Scope of Reference
Model
Ron:
I
will attempt to answer your question. If designing a service
oriented
architecture for an infratructure, yes - probably
none would exist
without messaging or messages. If you
use SOA principles to design a
single component (for example
- some sort of specialized services
server), it, by itself,
may not have any "messages" or mesage generation
software,
only a component of the service that recevies messages
from
other components (which I have been calling a "binding
mechanism"). So
if one were to ask the question " is
that services server SOA?", the
answer would be yes if it
had all the elements (which we have not yet
defined) of
SOA.
I hope this makes some
sense?
Duane
Schuldt,
Ron L
wrote:
>Team,
>
>I
agree in principle with Thomas and Duane. For the reference model,
I
agree that we should not be defining messages. Message
design is clearly an
implementation architecture
artifact.
>
>However, is any SOA
possible if there are no communications? I can't think
of
any example and I'm not saying one doesn't exist. If no example
exists,
then don't we need a communications element in the
reference model? If so,
then there would be a need for an
artifact called a communications
specification - although
the reference model would not define the content of
a
communications
specification.
>
>Ron
>
>
>-----Original
Message-----
>From: Duane Nickull
[mailto:]
>Sent: Wednesday, March 30,
2005 7:45 AM
>To: Thomas Erl
>Cc:
>Subject: Re: [soa-rm]
Architectural Scope of Reference
Model
>
>
>Thomas:
>
>Thank
you for this very elegant
summary!
>
>I think the answer
may be in the definition of a "reference model"
vs.
>"architecture". I think case studies will help
clear up this
>confusion. A reference model will
normally not contain "messages" as
a
>component.
>
>1.
Please look at the OSI Reference model. This is a
communication
>stack yet it does not contain
messages:
>http://www.scit.wlv.ac.uk/~jphb/comms/std.7layer.html
>
>This
does not contain any "message" although messages will occur
in
>implementations using the reference
model
>
>2. The ITA Reference
Model likewise does not have
"messages":
>http://www.ewita.com/earlywork/itarefr.htm
>
>3.
RCS Reference
Model
>http://www.isd.mel.nist.gov/documents/messina/euro_cast.pdf
>
>Again
- no messages even though there is an element
marked
>"Communications" in figure
one.
>
>The reference
Model should not contain "messages" as a component.
That
>belongs in architecture or implementations based on
the reference
>model. I have never encountered one
reference model with concrete terms
>in it. If it
had such, it would not be
abstract.
>
>We must think
abstract, not concrete.
>
>Duane
Nickull
>
>
>
>
>
>Thomas
Erl
wrote:
>
>
>
>>Some
thoughts regarding the on-going discussion of whether a
message
>>element should be part of our reference
model:
>>
>>As per our chosen
definition of architecture, in order to
describe
>>service-oriented architecture we need
to:
>>1. Define elements that comprise the structure
of a system.
>>2. Define external properties of these
elements.
>>3. Define relationships between these
elements.
>>4. Define the overall structure of the
system.
>>(not necessarily in this
order)
>>
>>Starting with the
first point, different element collections have
been
>>proposed in the two position papers submitted
so far. As has been
>>discussed, the MacKenzie/Nickull
paper does not identify a message
>>element, whereas
Kohring's does.
>>
>>A related
difference I noticed when reviewing these papers is
that
>>Kohring's establishes a broader range of SOA
elements. Specifically,
>>both service provider and
requestor (consumer) roles are separately
>>identified
and described. As mentioned in item #3 above, we
are
>>required to define the relationship between the
elements we define.
>>Therefore, it makes sense that
this paper includes a separate element
>>(message)
that can be used to help describe the relationship between
a
>>service and its
requestor.
>>
>>The elements
identified in the MacKenzie/Nickull paper are:
>>-
Service
>>- Service
Description
>>- A form of advertisement to facilitate
discoverability.
>>- Service
Contract
>>- Data Model
>>These
elements form a narrower architectural scope, leading to
a
>>proposed architecture that revolves primarily
around the service (or a
>>service assuming the
provider role). Because a service requestor is
>>not
explicitly identified as a separate element, it makes sense
that
>>an element representing some unit of
communication (message or
>>otherwise) is also not
identified. Within this model's scope,
the
>>definition of a relationship between a service
and its requestor
>>(beyond details implied by
description, contract, data model, and
>>advertisement
elements) is not a
requirement.
>>
>>I believe that
in order to address the issue of whether a message is
a
>>legitimate element within the reference model, we
should begin
>>by clearly defining the scope of our
abstract architecture. Given that
>>we are
establishing core elements that are expected to be present
in
>>all forms of SOA, this raises the question: Does
an architecture
>>require the presence of both a
service provider and a service
>>requestor (the coffee
shop and the patron) in order to be
classified
>>"service-oriented"? If yes, we must
define this relationship. To
>>properly do so, we very
well may need to further identify and define
a
>>separate element to represent an abstract unit of
communication passed
>>between
them.
>>
>>Thomas
>>
>>
>>
>>
>
>
>
>
--
***********
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Standards Strategist - Adobe Systems, Inc. -
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Vice Chair - UN/CEFACT Bureau Plenary -
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Adobe Enterprise Developer
Resources
-
http://www.adobe.com/enterprise/developer/main.html
***********
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Laskey
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