Re: [soa-rm-ra] Groups - Modification of Policy_Contract_Business diagram (OASIS_Policy-Contract_Diagram.JPG) uploaded

[Francis McCabe <frankmccabe@mac.com>]

Michael:
  I will try to answer your questions as clearly as I can. Forgive me  
if it is not sufficiently clear.

On May 5, 2007, at 3:21 PM, michael.poulin@uk.fid-intl.com wrote:

> I think we are on a "going around".
>
> Instead of juggling with examples, lets answer two simple questions:
> 1)	what the relationship, if any, between Service Contract and  
> Policies for all possible policies that could be applied to the  
> Service or service communication?

A contract is an agreement that constrains the future behavio(u)r and  
states of the participants agreeing to the contract.

The act of agreement may be implicit (e.g., by accessing a particular  
URL you agree to the constraints on service at that location); or  
explicit (e.g., I am not doing anything until you send me a message  
that matches this pattern: *I agree *.)

Notice how difficult it can be at the level of IT to distinguish  
implicit from explicit agreement.

I take a service contract to be a contract about one or more  
services. The contract description may include references to policies  
and other contracts -- either by reference or by direct inclusion --  
depending on the language used to describe the contract.

Other than the topics mentioned in the service contract, there is no  
a priori distinction between general contracts and service contracts.

As with contracts, so with policies. A policy description is a  
document that describes a policy; and because it is a description, it  
must use a language. That language constrains the forms and types of  
policies expressible in the description.

A policy description may contain references to other policies and  
contracts; again either by a link or by inclusion. (For example, I  
may have a policy to prioritize certain contracts over others.)


> 2)	what the relationship, if any, between Service Contract and SLA  
> (for all possible cases of SLA)?
>

I would say that the only significant conceptual difference between a  
service contract and an SLA that is possible is the topics mentioned  
in the contract. However, personally, I would need some convincing to  
distinguish these other than informally.

An SLA would seem to be focused on the run-time performance of a  
service; but that is only one view of SLAs.

We deliberately do *not* follow the WSDL approach of identifying a  
service with a single operation interface.  A service has one  
interface that includes all the actions that you may perform against  
the service and also includes any behavioral models associated with  
those actions (a.k.a. choreographies).

As for who will use the RA, we cannot be certain. But it is targeted  
as architects as well as others who are trying to understand what it  
takes to have an SOA.

Frank



>
> I am looking for your opinion while in my opinion (until I am  
> convinced in anything else), the answers are:
> to 1) - Service Contract may either include Policy or refer to the  
> Policy (equally true for multiple Policies); opposite is incorrect;
> to 2) - Service Contract may either include SLA or refer to the SLA  
> (equally true for multiple SLA); opposite is incorrect.
>
> The answers are based on the following assumptions:
> a)	if a client uses a service, client agrees with service  
> constraints that may include Policies among others
> b)	there are cases where explicit agreement between service client  
> and service provider is needed (i.e. explicit Service Contract) as  
> well as there are cases where agreement is implicit, i.e. the  
> client accepts/agrees with the service constraints without  
> additional negotiation and explicit agreement; the service  
> constraints may include Policies among others
> c)	SLA may include as all content of a Service Contract as only  
> some parts of it. If Service offers several interfaces, there may  
> be no SLA, one SLA for all interfaces or SLA per interface; the  
> Service Contract includes all related cases. ( NOTE: A service  
> interface is not just an operation, it is a means of service  
> contact in the communication with the service). For example, a  
> service can offer WSDL, IIOP/EJB, HTTP and JCA interfaces  
> simultaneously while a Service Contract with particular client may  
> include WSDL and IIOP/EJB interfaces only.)
>
> BTW, I have thought that SOA is not only a service oriented type of  
> business organisation but also is the business-centric type of IT  
> organisation which includes IT infrastructure... Will IT architects  
> be the users of SOA RA standard?
>
>
> - Michael