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Subject: Re: [soa-rm-ra] RE: updated service description

Title: Re: [soa-rm-ra] RE: updated service description
SLA can only encompass externally visible facets of a services operations, otherwise it is more or less moot.  Why would someone even contemplate saying “your service request will be treated with priority over al others” if there is no way to verify or authenticate from an external standpoint?  SLA’s should really just stick to things like timeouts, error reporting and other externally visible behaviors.

My $0.02.


On 2/25/07 2:21 PM, "Ken Laskey" <klaskey@mitre.org> wrote:


I started to respond to this hours ago, then printed out your paper, and finally make it past numerous distractions (including a unexpected 3 inches of snow to shovel) to finally collect my thoughts.

On your first point, I think of the service description as being the executive summary and table of contents.  It gives you the critical overview and tells you where to find more details.  So while Interaction Policies & Contracts in the description may explicitly lay out such things, these are more likely to be fully defined elsewhere and referenced from the description.  Of course, one benefit of this is that the policy, for example, becomes reusable.

As for the personal nature of policy agreements, if it is a one-time agreement,  I see it residing in the execution context (whose concrete manifestation is still to be discussed).  If the agreement is intended to be reused, it should be catalogued somewhere.  The idea of a general purpose somewhere also needs to be tackled, perhaps (definitely?) as part of the RA.

I then read your paper and if you went through the TC emails, you could find discussions touching on but never resolving many of these issues.  So here are some general questions and some specifics ones relating to your paper.

- What is a service component?  If we have a composite service, i.e. one that shows a single interface but is actually a combination of other services, do you consider the constituent services to be service components?  In the RM, we distinguish between the capability and the service that provides access to the capability.  Is an implementation of the capability also a service component?  Personally, I think I'd say yes to both where changes to either can affect the client experience.

- Are "service functions" the same as RM actions?

- One of my favorites: what belongs in a SLA?  Some views have it so complete that it basically becomes the service description, i.e. it describes functionality, constraints, interface details, and the birthdays of anyone who ever used it.  Personally, I take a more minimalist approach and think of SLA as being strictly a set of well defined metrics against which compliance can be measured.  I agree with with your line that "a SOA service ... is invoked ... when the client is fully aware of the service behavior and conditions."  (We could quibble over "fully".)  To accomplish this, I rely on an adequate service description, of which a metrics-laden SLA is a part.  However, another part is an indication of how one can obtain metrics collected against the service.  It is then up to the client to compare the collected metrics with the SLA and determine fitness for use.  For example, if I have a service that says I will relieve 80% of world hunger and the metrics show me only relieving 70%, does my service provide value?

Enough for now.


On Feb 25, 2007, at 10:00 AM, michael.poulin@uk.fid-intl.com wrote:

Hi Ken,
 I have two notes to the update (actually, to the doc as it is with the update):

1) There is an entity in the Service Description diagram named "Interaction Policies & Contracts". I think that Contract belongs to another area than service description because it is 'personalized' based on consumer/provider agreement. Yes, logically, a Contract is a special type of description but it would be more comprehensive if we put it into Interacting with Services Model  section. 

2) You have mentioned <A discussion of how version designation/value should be impacted by change of version of any of its components (or any descriptions?) still needs to be discussed.> To me, a version of the service is one of very important characteristics of the service description (and, respectively, of the service contract). I would propose placing version as an entity in the Service Description diagram either under Identity or at the level of Service Description entity because version affects Service Reachability, Service Functionality, Interaction Policies, and Service Interface entities. I have published a few thoughts about SOA service versioning in SOA-WebServices Journal (http://java.sys-con.com/read/250503.htm ).

- Michael

Ken Laskey
MITRE Corporation, M/S H305     phone:  703-983-7934
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