Thin vs Thick

[Francis McCabe <frankmccabe@mac.com>]

The RM defines service as:

A service is a mechanism to enable access to one or more capabilities,  
where the access is
provided using a prescribed interface and is exercised consistent with  
constraints and policies as
specified by the service description.

The RM does not define the concept of participant, and is explicitly  
vague about service consumers and service providers.

(In fact, one could argue that the correct title for the RM should  
have been "Reference Model for Service"; rather than Service Oriented  
Architecture.)

We have a different job, in particular, we have to gain clarity on the  
relationship between participants and services. This is one of the key  
responsibilities of the Service as Ecosystem view.

In the service (sic) of that clarity, we introduce the concepts  
involved in capturing the fact that participants are acting in the  
context of a SOA.

Looked at from the perspective of a participant, it seems clear to me  
at any rate, the key idea is that a SOA presents the participant with  
a bunch of levers that can be manipulated in order to 'get things  
done'. More specifically, most of the levers involve (business)  
relationships that I may have with other participants and transactions  
that I wish to execute with those participants.

There is some uniformity to those levers: they have descriptions and  
mode of operation of those levers is based on communication. This is  
like saying that all the active elements of a UI are presented as  
buttons, and each button has a label and a tooltip. The uniformity is  
key to *realizing* and *using* a SOA-based system but does not  
materially affect *what* participants are trying to do.

So, again from the perspective of a participant, the participant can  
be seen as *using* the SOA-based system to get things done. Using a  
SOA-based system means *acting* against services or *providing*  
services (or some other combination such as *mediating* services).

I believe that if you start from this perspective, then you have to  
explain a couple of things: what does it mean to *act* against a  
service, and how do you use communication to do so. This is quite  
difficult to disentangle, especially when you consider the fractal  
nature of everything; and even sending a message can be viewed as a  
kind of action.

We must also remember to capture the relationship aspect as well as  
the transactional aspect. This is where the *social structure*,  
*role*, *right* and *responsibility* show up.

One way of doing all of this is to take a foundational approach: we  
build up layers that each address different aspects.

One such stack within the Ecosystem viewpoint could look like this:

Layer 0.a: Action, Actor, RWE

Layer 0.b: Participant, Agent, Stakeholder

Layer 1.a: Joint Action, Communicative Action

Layer 1.b: Social Structure, Social Action, Social Fact,  
Ownership(Resource)

Layer 2: Service Action, Transaction

Layer 3: Role, Rights, Responsibilities, Governance

(This stack is offered as a guide: I have no special investment in it.)

So, to address the thick vs thin question. I am arguing that the  
question of whether service is thick or thin depends on your  
viewpoint. From the perspective of a participant, it seems pretty thin  
- it is a means by which the participant's actions are mediated. From  
the perspective of realizing, offering and discovery it seems pretty  
thick.

This is one reason why we have multiple viewpoints :)

Frank

smime.p7s