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Subject: Re: [soa-rm-ra] Questions on action model
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 > > scott.came@search.org > > >
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