Scott,
I think that you are right about actions wrt RWE. We have not
'unpacked' the RWE a great deal in terms of actions; but yes, the
atomic components of RWE are going to be from actions.
However, I am not sure that there is much need to fully elaborate
this in the RA. I am willing to be persuaded either way.
Frank
On Oct 8, 2007, at 9:39 AM, Scott Came wrote:
> I have some questions regarding draft 0.2 of the RA, in the area of
> the action model. I scanned the list archives for answers, and
> none were readily apparent, so…
>
> Regarding lines 1011-1015, there is a statement that real world
> effects (note the plural) are defined for a service, not the
> individual actions on a service. Similarly, policies are
> associated with the service and not individual actions.
>
> I am struggling with the practical implications of this.
>
> It seems if you allow a service to produce multiple real world
> effects, and the plurality of effects is of significance to
> consumers, then at least in some cases I would think you’d want to
> provide independent access to those. (Otherwise, you may as well
> just roll them all up into one macro “effect”.) So, if you accept
> that a consumer may choose to achieve some of a service’s effects
> and not others during a particular interaction, how would the
> consumer do so other than by invoking specific actions? And, if
> the consumer is to invoke specific actions to achieve particular
> effects, wouldn’t the service provider necessarily need (per
> awareness) to tell the consumer which actions produce which
> effects? Otherwise what distinguishes the actions?
>
> An example may help… A corporate accounting department provides a
> service for business units to use in managing employee timesheets.
> (The corporation is large and diverse enough that business units
> may build their own time accounting systems, but by policy everyone
> must access the central corporate capability for some basic
> functions.) The time accounting service provides access to basic
> CRUD capabilities for employee time: add time records, read (view)
> them, update existing ones, and (perhaps) delete records under
> certain circumstances. If you are willing to grant that these four
> actions (create, read, update, delete) are appropriate within a
> single service action model, then clearly they produce distinct
> (though related) real-world effects (underneath the “umbrella”
> effect of “manage employee time records”), and certainly will have
> different policies associated with them (there may well be tighter
> access control on changing data than viewing data, for example).
>
> A possible objection to this characterization of the service is
> that it tightly couples each of the four C/R/U/D operations in a
> single service. The problem with this objection is that there is
> no universal benchmark for tight-coupling. Coupling and cohesion
> are competing forces that need to be balanced in any design
> decision. Achieving that balance is an engineering problem solved
> based on the particulars of the situation. In an SOA, since one of
> the primary objectives is agility and resiliency, I would hope the
> architect would make that decision primarily on the basis of
> whether the four actions are likely to change at the same time, or
> not at all. But certainly other factors may come into play.
>
> It seems you would want to give the architect the freedom to
> achieve the right balance there, rather than force his or her hand
> by saying services must be designed such that the actions do not
> achieve distinct objectives and do not have distinct policy
> requirements.
>
> This line of reasoning may be completely out in left field;
> however, if it is, I would urge some more thorough discussion in
> section 4.2.2 of how service design principles should impact the
> scoping of services, their RWEs, and their action models.
>
> I also have one more specific follow-up question, not addressed in
> section 4.4.1.2: In an RA-conformant concrete architecture (as
> such is envisioned now), can the actions in a single service’s
> action model use different MEPs? Can one action use request/
> response and another use event notification?
>
> Thanks for your help!
>
> --Scott
>
> Scott Came
>
> Director, Systems and Technology
>
> SEARCH--The National Consortium for Justice Information and Statistics
>
> (916) 212-5978
>
> (916) 392-2550 x311
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>
