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Subject: Re: [soa-rm-ra] Disambiguating Action (Part I)


A nice layout of the problem.

I'll need to work on all the questions later but let me add what I meant by Capability when I contributed to and have since explained the RM, and where I thought things fit together when contributing to the RA.

There are 59 occurrences of capability (singular  or plural) in the RM.  Over half occur in section 2.1: the first is the definition of SOA:

Service Oriented Architecture (SOA) is a paradigm for organizing and utilizing distributed capabilities that may be under the control of different ownership domains.

This is immediately followed by

In general, entities (people and organizations) create capabilities to solve or support a solution for the problems they face in the course of their business.

The RM was careful to avoid using the term service to define SOA when service itself hadn't been defined, so this discussion occurs before any mention of service.  After that, service is informally defined (the formal definition is in section 3) through

These concepts emphasize a distinction between a capability and the ability to bring that capability to bear. While both needs and capabilities exist independently of SOA, in SOA, services are the mechanism by which needs and capabilities are brought together. 

This is where I sometimes use the term "underlying capability".  The capability exists outside of SOA and is part of the black box through which certain RWE can be made to happen; the service tells the capability to do (some subset of) its stuff.

Functionality is the general description of what "business service" is accomplished by using the capability or the service that accesses it.  In an earlier email, I said (for our current endeavor) I didn't care what functionality was possible from a capability; the important thing was the functionality that a service accessing the capability could deliver.  If I combined a number of underlying capabilities to form a service, it is the combined functionality with which I am concerned.

The real world effects are the specific things that happen when I use a capability or a service.  Again, I am not interested in the RWE of the capability, only those RWE accessible through the service.  For the RM, Frank introduced the concept of RWE as the accumulation of changes to shared state, and we expanded this to include an information response to something like an HTTP GET where there was no obvious state change.

As you noted, Action is not defined in the RM, but we talk about "invoking a service" or "actions being invoked against a service".  There was no intent to use the term invoke to make explicit connections with distributed computing models; again, we chose a term from an already overloaded English language.

So that's where we stand going into the RA.

Now when I come along for the RA and try to start writing about service description, I need to figure out how some of these pieces work; otherwise, I don't know what information I need to convey to actually use those pieces.  I also want to make the point that service description is not a random collection of documentation but is actually an indispensable compendium of critical information needed to use a service.  To do that, I need to connect the pieces, and that's why I draw together the leaf nodes in the artifact in Figure 20 and connect these in Figure 26 to what I saw as the unifying concept: the Action.

Now my interpretation when writing this was that Action was somewhat the same (allow me to be fuzzy here) as the WSDL operation.  An Action is initiated by receiving a message at the identified endpoint, using the identified protocol, carrying the necessary information corresponding to the the identified structure and semantics, and conforming to identified policies and contracts when realizing the identified RWE.

Is this inconsistent with the "application of intent"?  Not necessarily because Action as I used it is the bringing together of pieces that enables you to actually apply the intent.  Or at least I can look at it that way.

As for the visual model in Figure 10, it is missing a connection between Intent and Action.  I would say the Participant has a Goal (not currently in model) that is committed to through Intent, and Intent is applied through Action.  Additionally, the Participant employs an Agent to perform Action as currently shown, but I wouldn't has a connection between Intent and RWE.

I'll put off working through the various roles of Participant until later.


P.S. As a quick aside: when actually solving a problem, I am more interested in the available capabilities than I am in the service.  I want to be able to get things done, and the fact that some SOA service can provide access to the capability may have a decisive effect on how I construct my solution, but I can't do anything unless I can make use of the appropriate capabilities.  One of my problems with service registries is I think they are emphasizing the wrong part of the solution.

On May 23, 2008, at 2:03 PM, Jeffrey A. Estefan wrote:

OK Folks,
The hot topic of the day is "Action."  Here is my initial (Part I) attempt based on interpretation of the content described in the RM v1.0 Std and the RA v1.0 PRD1 and mapped to one of the simplest examples of a service offering, the classic temperature conversion service.  I do not propose to have all the answers here.  Where there are open questions, I will note them with the hope that these questions will spur conversation from the RA editors and SC members who have been actively engaged in discussion surrounding this topic.  I encourage you to read through the entire note before responding to the individual open questions summarized below.
So let's get started...
Believe it or not, in the RM, we use the word "action" ten times and the plural "actions" twenty-seven times, yet we never actually defined what action is.  We introduced the notion of an Action Model and defined it to be "the characterization of permissible actions that may be invoked against the service," but never action.  We were very careful about distinguishing between "private action" from "public action," but again, we did not define action.  This is why it was important for us to do so in the RA.  Indeed, Frank did so on lines 754-755 of the RA PRD1.  Here, Action is defined as "the application of intent by a participant (or agent) to achieve a real world effect."  We'll come back to this definition and its associated models in a bit, but first, let's elaborate more on the Action Model.
For a simple temperature conversion service that has the capability of converting degree expressed in Fahrenheit units to degree expressed in Celsius (centigrade) and vice versa.  The service's functions are two: 1) given a numeric value that represents degree Fahrenheit, return a numeric value that represents degree Celsius, 2) given a number value that represents degree Celsius, return a numeric value that represents degree Fahrenheit.  Simple enough, right?  So what is the Action Model for this service?  From a implementation technology point of view, this service could be implemented using a distributed object computing model, which exposes two operations that represent the two functions described above.  For the sake of this discussion, it does not matter whether that technology is Java RMI, CORBA, Jini, .NET, COM+, DCOM, Openwings, XML Web services, or some other distributed object computing technology.  It's just that in order to realize this service, at least in today's world, it's likely to a variant of a distributed object computing model that exposes remote operations (functions) that the consumer can invoke.
So again I ask, what is the Action Model for this service?  Well, it has to be a description of those two functions, right?  The reason I am making this point is because of the operative word "invoke" in our definition of Action Model.  This leads to the question of functions versus "characterization of the permissible actions that may be invoked against the service," which, of course, defines the Action Model.  We don't spend a lot of time talking about functions in the RM with the exception of Service Functionality, which is part of the Service Description artifact.  On lines 602-603 of the RM, the sentence reads "A service description SHOULD unambiguously express the function(s) of the service and the real world effects (see Section 3.2.3) that result from it being invoked."  But that also sounds like Capability.  So as you can see, we've already introduced some ambiguity in our model that we need to resolve.  How do we distinguish between functions (or functionality) and capabilities (or capability) and permissible actions (or Action Model)?  Do the permissible actions correspond to operations?  Or is that an implementation detail?  I suspect the latter, and why the RM was wise in using "action" instead of "operation."
Now let's return to the RA in which Action is finally defined.  For this discussion, I am referencing the material described in Section 3.5.1 Actions, Real World Effects and Events.  As noted earlier, this is the Section in which I feel Frank has done a fairly nice job in defining what Action really is, which is "the application of intent by a participant (or agent) to achieve a real world effect."  That seems reasonable enough.  Now, let's explore the visual model shown in Fig. 10 (line 766).  This model depicts the relationships between key concepts such as Action, Intent, Event, and Real World Effect.  Well, we know from the RM that the Real World Effect (RWE) is the actual result of using a service (as opposed to the capability being offered).  On lines 767-769 of the RA PRD1, Frank introduces yet another definition of RWE and to be honest, I don't think we should do that.  In fact, in the RA, we should not create new definitions of core RM concepts at all.  We should only define terms like Action that were not specified in the RM.  But I digress.  We should capture this point in our issues spreadsheet.  What is more important here is to disambiguate the model depicted in Fig. 10.
Here, Participant is used.  But we know from the Stakeholders and Participants Model of the RA (Section 3.1) that a Participant can be a Service Consumer, Mediator (third party), or Service Consumer.  If we were to replace Participant with say Service Provider in Fig. 10, does the model still work?  And where does the Service itself fit into the model?  If indeed Participant were Service Provider, one could envision the Agent to be the Service.  Is this a fair assumption Frank?  Open question.  And what would this mean in terms of Event?  Would a Service Provider care about events?  The only scenario I see that happening is in a V&V scenario.  In other words, the Service Provider or some entity (person or organization) working on behalf of the Service Provider is engaged in testing the Service prior to exposing its capabilities to the world.  Here, the Service Provider or supporting entity would actually be acting in the role of Service Consumer (for testing purposes) and Events could be relevant.  Again, open question to Frank.
Now, if we were to assume the Participant is a Service Consumer (or Mediator), does the model still work?   Kind of.  Where I think it breaks down is, again, on Action.  What action does the Service Consumer perform?  Is it sending a message?  Well, we don't get into that here.  And does just sending a message (which can certainly be consider an action initiated by the Consumer) cause the RWE to occur?  Certainly just sending a message cannot.  It is the actions performed by the Service Provider Agent (i.e., the Service) that are invoked as a result of the Service Consumer Agent sending the appropriate message that leads to a RWE.  So now the argument for Joint Action starts to become clearer (we think!).  But I will defer the discussion surrounding Joint Action until next time.  For now, let's see if we can resolve some of the potential ambiguities w.r.t. the Fig. 10 visual model I just described.
Summary of open questions and gut responses (looking for yours!):
1) How do we distinguish between Capability (or Capabilities), Functionality (or Functions), and Action Model (permissible Actions)?
For me, at least, it seems that Capability is at a higher level of abstraction than Functionality.  Capability could be described in natural language text that is part of summary description of the service, contained, of course, in its Service Description artifact, which could be included as a service registry-repository entry.  In terms of the simple temperature conversion service described above, Capability could be a simple brief description of what the service does without getting into the specifics of the underlying functions.  As with Capability, Functionality could be described in natural language text that is part of the Service Description artifact.   In terms of the simple temperature conversion service described above,  Functionality would be a bit more granular and would describe the two functions that the service offers; one from degree Fahrenheit to degree Celsius and the other from degree Celsius to degree Fahrenheit.
The Action Model (permissible actions) is very similar to Functionality (functions) except that the description of the permissible actions is intended for consumption by humans and non-human agents as part of the Service Interface, which is a critical component required at design time.  An example of a design time scenario is the following:  A human(s) uses the Action Model described in the Service Interface to construct code that would invoke the actions exposed by the Service.  From an implementation perspective, these actions would likely correspond to invocations on remote operations.  We do not make the connection between Action Model and Service Interface very clear in the RM with the exception of drawing a simple directed line from Behavior Model to Service Interface in Fig.  9 (line 565).  I did not see evidence of any text in the RM that supports this linkage, which is OK except that it leaves open some ambiguity.
What is not yet clear, is what role the Action Model has at run time (Interaction).  Perhaps none!  Maybe this is the point Frank is trying to make in distinguishing Action (which is not the same thing as Action Model) from Joint Action and Communicative Action, described in Sects 3.5.3 and 3.5.4 of the RA PRD1.  That said, I'd prefer we defer that discussion until Part II if we can.
2) Does the visual model depicted in Fig. 10 of the RA PRD1 (line 766) hold up for different types of Participants, i.e., Service Consumer, Mediator, and Service Provider?  How does Event play out in a Service Provider Participant role?
I do not have a gut response to this open question.  Please see my earlier discussion notes around this topic.
3) What is the role of the Service, currently not depicted in the model of Fig. 10. nor described in the supporting text?  From the Service Provider perspective, is it the Service Provider Agent that represents the Service?
I do not have a gut response to this open question.  Please see my earlier discussion notes around this topic.
Next time, I'd like to focus on Joint Action and how it relates to Interaction.  And the role of messages and message exchange to Action.  Maybe the latter will be a Part III discussion, we'll see.
Hoping for a spirited discussion that will hopefully converge on disambiguating Action for not only us but for our readers at-large!
 - Jeff E., JPL

Ken Laskey
MITRE Corporation, M/S H305      phone: 703-983-7934
7515 Colshire Drive                         fax:       703-983-1379
McLean VA 22102-7508


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