Even if I disagree,
This is the first step.
So now a few more questions:
·
How is mediator differ from composite service, which actively
controls complex interactions between services?
·
What about fairly simple mediators for request routing, data
transformations and security?
·
What about mediators that are put in place just to
control/monitor usage?
From: James Odell
[mailto:email@jamesodell.com]
Sent: Thursday, December 16, 2010 10:24 AM
To: soa-rm-ra@lists.oasis-open.org
Subject: Re: [soa-rm-ra] Re: Further Note on Mediator
Have used word service to define a
mediator, because I use the mediator as a kind of service — as such, it is a
subclass of service, because it is a specialized form.
What differentiates it from a general service is that it provides a
specialized functionality: i.e., a Mediator [actively] controls complex interactions
based on complex relationship.
-Jim
On
12/16/10 3:41 AM, "Lublinsky, Boris" indited:
With all these alphabet puns and money exchanges my questions
remains unanswered. Here is the list:
· Is
mediator a service (Jim used the word service to define a mediator)
· If it
is, why are we using both words – mediator and a service. What distinguishes
mediator services from other services?
· If it
is not, then what distinguishes it from the service? Size? Specific
functionality?
I think those are the base questions that we need to answer to
lift this discussion from hand waiving to specifics.
From: James Odell [mailto:email@jamesodell.com]
Sent: Wednesday, December 15, 2010 4:46 PM
To: soa-rm-ra@lists.oasis-open.org
Subject: Re: [soa-rm-ra] Re: Further Note on Mediator
Glad you
appreciate alphabet puns. :-)
Maybe, I should have said “control”, instead of “manage.”
“Participate” has passive overtones, whereas “control” for a mediator would
yield:
[actively] control complex interactions based on complex relationship.
But, it’s not work splitting too many hairs. That’s what got SOA RM into
trouble a few times.
-Jim
On 12/15/10 5:33 PM, "mpoulin@usa.com"
indited:
I value your humor, Jim: you say 'manage' + I say 'does not manage'
I say '1 p. (i.e. pence)' +you say 'Ruble' (where P is Russial 'R')
- Michael
-----Original
Message-----
From: James Odell <email@jamesodell.com>
To: soa-rm-ra@lists.oasis-open.org
Sent: Wed, Dec 15, 2010 10:10 pm
Subject: Re: [soa-rm-ra] Re: Further Note on Mediator
Michael,
Your definition looks similar enough to mine, so it works for me.
My 1/2 Ruble.
-Jim
On 12/15/10 3:17 PM, "mpoulin@usa.com"
indited:
From the time of GoF, mediator was never an managing entity, it always was a
supporter of complex relationships between those who managed these
relationships (and made them complex). I would strongly oppose an idea that a
third party were managed my relationships until I hire this party for managing
purposes.
So,
mediator, to me, is the one who realizes, provides complex interactions based
on complex relationship, and nothing more. This is why I criticizes ESB system
vendors for are crossing the line and taking over management.
My 1p.
- Michael
-----Original
Message-----
From: James Odell <email@jamesodell.com>
To: soa-rm-ra@lists.oasis-open.org
<soa-rm-ra@lists.oasis-open.org>
Sent: Wed, Dec 15, 2010 7:23 pm
Subject: Re: [soa-rm-ra] Re: Further Note on Mediator
Boris,
For SOA and non-SOA implementations of agents:
A Mediator can be thought of as a service that offers functionalities that manage
collaboration/interactions and act as an intermediary between entities.
With this definition, a mediator does not have to be software. If it
does, then it would be a “software-based mediator.”
My 2 cents.
-Jim
On 12/15/10 1:42 PM, "Lublinsky, Boris" indited:
Thanks Jim.
The question then is where we should draw the line between services and
mediators?
At which point a service becomes a mediator? Or in your mind they are the same?
From: James Odell [mailto:email@jamesodell.com]
Sent: Wednesday, December 15, 2010 11:20 AM
To: soa-rm-ra@lists.oasis-open.org
Subject: Re: [soa-rm-ra] Re: Further Note on Mediator
Boris,
In my experience, using agent-based software, mediators are not necessarily “light
weight” -- and they can be composite services, as well. In event-driven
systems within SOA, this is particularly true. In large SOA systems,
mediators are often employed as complex in service selection; for example,
employing mediators as auction-based mechanisms (e.g., British auction, Dutch
auction, Japanese auction, etc.).
-Jim
On 12/15/10 11:37 AM, "Lublinsky, Boris" indited:
Rex,
I am sorry, but this does not make sense. If we will continue this line of
thought then every service is a mediator.
Mediator is typically a light weight component that doing on or more of
following:
· Data
transformation to align data models mismatch
· Versioning
support
· Routing
based on external registry
· SLAs
support, for example authorization
· Additional
monitoring and load balancing
Mediator is NOT a composite service implementation, which means
that it does NOT:
· Implement
additional business functionality
· Orchestrate
service execution
From: Rex Brooks [mailto:rex.brooks@ncoic.org]
Sent: Wednesday, December 15, 2010 9:57 AM
To: rex.brooks@ncoic.org
Cc: mpoulin@usa.com; danny_thornton2@yahoo.com; soa-rm-ra@lists.oasis-open.org
Subject: [soa-rm-ra] Re: Further Note on Mediator
Hi again,
I wanted to add one last clarificationof my opinion to the discussion on
Mediator. I would support adding "orchestration conductor-controller
software" as another example of a mediator. I only object to restricting
the definition to such software.
Cheers,
Rex
On 12/13/10 9:31 AM, Rex Brooks wrote:
I think we are talking about different things when we use the word mediator.
Let's discuss further.
Cheers,
Rex
On 12/9/10 11:57 AM, mpoulin@usa.com wrote:
Well, Rex, I
also fail some times in convincing people in things that are obvious to me.
This is
not about voting because I also haven't quit yet. The time with judge. Four
years ago, when I said that Web Services were not services, people looked at me
like I was crazy; now, many look at people who still take WS as services like
they are crazy...
As you
know, one fact can break any perfect theory; I am looking for such fact for you
-
Michael
-----Original Message-----
From: Rex Brooks <rexb@starbourne.com>
<mailto:rexb@starbourne.com>
To: mpoulin@usa.com
Cc: danny_thornton2@yahoo.com; soa-rm-ra@lists.oasis-open.org
Sent: Thu, Dec 9, 2010 3:58 pm
Subject: Re: [soa-rm-ra] Strawman of outstanding issues
You
haven't convinced me, Michael,
So perhaps we'll have to just have a vote.
BTW, I have never understood the tendency to insist on unanimous consensus.
It's nice, yes, but not necessary. I lose a lot of votes across the spectrum of
committees and organizations in which I participate, but I haven't quit yet. I
believe we can survive some votes and if I'm on the losing side, I will be
happy to accept it.
Cheers,
Rex
On 12/8/10 3:39 PM, mpoulin@usa.com wrote:
I understand that you had just a quick look at the article.
Facade
and Mediator are referred in different parts of the article and the only common
things among them noted in the article is that both of them used incorrectly in
the SOA Design Patterns book as well as in practice.
Particularly,
ESB as a Mediator has no rights to add any business functionality on the top of
mediation agreed between consumer and service. If no mediation is explicitly
agreed, no additions beside message routing are allowed in the ESB (according
to RAF). Facade is "recommended" to be placed between service
interface and the service, which is not only violates the definition of Facade
as interface-interface transformation means but it makes no sense at all for
SOA service (being in the mentioned position).
"mediated
awareness"
is a quality of the entities that are aware; awareness cannot belong to a 3rd
party while 'awareness _about_ 3rd party' is a regular use of the term
awareness.
Registry-Repository
cannot
be a Mediator because, as you said, "Mediator is a behavioral pattern " and Registry-Repository doesn't have
its own behavior regarding entities that use it, i.e. it cannot mediate between
them.
-
Michael
-----Original
Message-----
From: Danny Thornton <danny_thornton2@yahoo.com>
<mailto:danny_thornton2@yahoo.com>
To: soa-rm-ra@lists.oasis-open.org;
mpoulin@usa.com
Sent: Wed, Dec 8, 2010 10:17 pm
Subject: Re: [soa-rm-ra] Strawman of outstanding issues
The text is using a third party Registry-Repository as
one example of mediated awareness - there can be many ways to provide
awareness. Mediator is a behavioral pattern and in this example the behavior is
mediated awareness. As chair Ken mediates SC meetings, MatchMaker.com
mediates people meeting each other, etc.
The article in the link seems to use facade and mediator synonymously.
Facade is structural. I have created many a facade for business logic
and underlying data access. Facade tells me about an architectural
structure. It may be that my facade is just a wrapper on entity beans to access
DB tables in which case I would not denote it as a mediator in the
architectural description.
Danny
--- On Wed, 12/8/10, mpoulin@usa.com <mpoulin@usa.com> wrote:
From: mpoulin@usa.com <mpoulin@usa.com>
Subject: Re: [soa-rm-ra] Strawman of outstanding issues
To: danny_thornton2@yahoo.com, boris.lublinsky@navteq.com, soa-rm-ra@lists.oasis-open.org, peter@peterfbrown.com
Date: Wednesday, December 8, 2010, 1:15 PM Danny,
I am really interested in reading your comments on my article "Patterns In The Context of SOA
Business Services <http://www.infoq.com/articles/patterns-soa-business-services>
" (http://www.infoq.com/articles/patterns-soa-business-services)
A
mediator MAY be known to service consumers and services/providers. Yes, you put
this Mediator into the Service Description and, respectively, into the Services
Contract, no problems. However, awareness and registry-repository have NOTHING to do with each other IMO while
I have the same understanding of registry and repository as you describe.
I
believe that the statement "Mediated
awareness promotes loose coupling by keeping the consumers and services from
explicitly referring to each other and the descriptions" and "Mediation lets interaction vary
independently"
contradicts 90% of current RAF. In SOA, not in Web Services, consumer and
service/provider MUST know each other ( as in Business ) to agree on the
service use, to sign the Service Contract.
Interaction
between consumer and service MAY NOT be independent from them, it is not
service orientation. Service registry/repository STORES information and nothing
more. Consumers can use them or ignore them, it is up to them, we have no
controls over them to enforce usage of registry/repository.
Saying that re-direction via registry/repository is a good thing may be
possible in only one case: participants of the consumer-service interaction are
aware about such indirection. This is why I am saying that ESB pattern has been
incorrectly represented in the form of ESB products. ESB may not hide
interacting actors, it has only simplify this interaction.
- Michael
-----Original
Message-----
From: Danny Thornton <danny_thornton2@yahoo.com>
To: BorisLublinsky <boris.lublinsky@navteq.com>;
soa-rm-ra@lists.oasis-open.org
<soa-rm-ra@lists.oasis-open.org>;
Peter F Brown at work <peter@peterfbrown.com>
Sent: Wed, Dec 8, 2010 8:27 pm
Subject: RE: [soa-rm-ra] Strawman of outstanding issues
Within the context of the SOA RAF, Section 4.2:
Service
consumers <http://us.mc556.mail.yahoo.com/mc/welcome?.gx=1&.tm=1291827748&.rand=er2um5167fcag#ServiceConsumer>
and service providers may have direct awareness or mediated awareness
where mediated awareness is achieved through some third party.
A common mechanism
for mediated awareness is a registry-repository. The registry stores links or
pointers to service description artifacts. The repository in this example is
the storage location for the service description artifacts.
Mediated awareness
promotes loose coupling by keeping the consumers and services from explicitly
referring to each other and the descriptions. Mediation lets interaction vary
independently.
--- On Wed, 12/8/10, Peter F Brown at work <peter@peterfbrown.com <http://us.mc556.mail.yahoo.com/mc/compose?to=peter@peterfbrown.com>
> wrote:
From: Peter F Brown at work <peter@peterfbrown.com
<http://us.mc556.mail.yahoo.com/mc/compose?to=peter@peterfbrown.com>
>
Subject: RE: [soa-rm-ra] Strawman of outstanding issues
To: "Lublinsky, Boris" <boris.lublinsky@navteq.com
<http://us.mc556.mail.yahoo.com/mc/compose?to=boris.lublinsky@navteq.com>
>, "soa-rm-ra@lists.oasis-open.org
<http://us.mc556.mail.yahoo.com/mc/compose?to=soa-rm-ra@lists.oasis-open.org>
" <soa-rm-ra@lists.oasis-open.org
<http://us.mc556.mail.yahoo.com/mc/compose?to=soa-rm-ra@lists.oasis-open.org>
>
Date: Wednesday, December 8, 2010, 12:09 PM So registry is also a service but
not part of 'the' service that is playing the role of provider? Is it a service
performing a different role? It's capability offering being rather specialized
(eg service discovery)? Going back to the model, is it simply another (of
potentially many) role played by a participant in the ecosystem?
Peter F Brown
Independent Consultant
www.peterfbrown.com <http://www.peterfbrown.com>
<http://www.peterfbrown.com/>
@pensivepeter
+1.310.694.2278
Sent from my Windows Phone - Apologies for typos, levity and brevity -
it's hard to type on a moving planet
From:
Lublinsky,
Boris
Sent: Wednesday, 08 December, 2010 6:48
To: peter@peterfbrown.com <http://us.mc556.mail.yahoo.com/mc/compose?to=peter@peterfbrown.com>
; soa-rm-ra@lists.oasis-open.org
<http://us.mc556.mail.yahoo.com/mc/compose?to=soa-rm-ra@lists.oasis-open.org>
Subject: RE: [soa-rm-ra] Strawman of outstanding issues
> Peter,
> This is a good deck.
> A couple of comments:
>
>
>
> Mediator
>
>
>
> -? is a registry a good example? Do we have better ones? Is it more
than mediator?
> I do not consider a registry to be a mediator. A registry is a
specialized entity in his own right with its own set of goals.
> Typically a mediator is an entity that is invoking service on behalf
as a consumer and is seen by consumer as a service (compare to proxy in a
distributed system). The difference between mediator and a simple proxy is
significant - mediator is more like an interpreter in a conversation between
people speaking different languages. Typical mediators do the following -
transport transformation (for example MOM to HTTP), semantic alignment (data
transformation), dynamic routing, often leveraging registry (version-based
routing, etc)
>
> I am not sure how Skill is relevant for SOA
>
> I have a real issue with introducing resources into SOA. The problem
is Resources are orthogonal to services - it is a completely different model of
the world - see REST vs SOA. A service implementation internally does depend on
resources, but this is opaque to the service consumer.
> The issue here is that SOA is based on the functional decomposition,
where functions can cross resource boundaries, where Resource decomposition is
based on identifying resources, regardless of services they provide. A system
can be build either way, but those will be 2 different systems. The
relationship is similar to entity beans (resource) vs session beans (services).
>
> Semantics is a really hard one. The issue is that in SOA semantics
is defined by service provider. It is NOT specific to a consumer/provider pair.
A service consumer can have his own semantics, but he typically has to use a
mediator for resolving semantic differences
>
>
> From: Peter F Brown [mailto:peter@peterfbrown.com
<http://us.mc556.mail.yahoo.com/mc/compose?to=peter@peterfbrown.com&>
]
> Sent: Tuesday, December 07, 2010 8:09 PM
> To: soa-rm-ra@lists.oasis-open.org
<http://us.mc556.mail.yahoo.com/mc/compose?to=soa-rm-ra@lists.oasis-open.org>
> Subject: [soa-rm-ra] Strawman of outstanding issues
>
> Hi:
> We have worked through the entirety of outstanding issues, questions
and concerns for section 3 (along the way, examining also sections 1 & 2).
We have, inevitably many, many, edits to propose!
>
> However, and as promised on last week's call, we now present a
"Strawman", in the form of the attached slide deck which we think
touches on all the main issues and provides a narrative for addressing them.
>
> We stress this is not an editing exercise but an attempt to gain
consensus on the main issues, definitions and relationships between terms
before the proceeding with presenting detailed dispositions of textual changes,
in line with said consensus.
>
> As previously announced, I will not be able to join the call
tomorrow as I'll be some 30,000 feet over Kansas at the time of the call. Chris
Bashioum will lead off as your Maître d'
>
> Regards,
> Peter
>
> Peter F Brown
> Independent Consultant
> [cid:image001.png@01CB96AC.EA7AD190
<http://us.mc556.mail.yahoo.com/mc/compose?to=image001.png@01CB96AC.EA7AD190>
]
> Transforming our Relationships with Information Technologies
> www.peterfbrown.com <http://www.peterfbrown.com>
<http://www.peterfbrown.com/>
> @pensivepeter<" target=_blank rel=nofollowhttp://twitter.com/#!/@pensivepeter>
<http://twitter.com/#%21/@pensivepeter>
;
> P.O. Box 49719, Los Angeles, CA 90049, USA
> Tel: +1.310.694.2278
>
>
>
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