Re: Compositions Types:Static and Dynamic

On Apr 12, 2006, at 4:03 AM, Daniela CLARO wrote:

>
> Hi all,
>  I want to hear from you about composition types. Actually, I 
> classified
> the composition of sws in two categories: static compositions and
> dynamic compositions.
> From static composition I mean the compositions that know iin advance
> all services that will belong to the composition, for example, the use
> of workflows, that we decide before which services will participate to
> the compostion. Do you have other examples from static compositions?

I tend to call this a fully grounded composition. That is, a workflow 
where all the service invocations are bound to particular concrete 
services. I don't think this is *static* because it's pretty easy to 
imagine replacing one of the concrete services with an equivalent on at 
execution time (say, due to the unavailability of the original 
service). That is, a system with a robust recovery (or aggressive 
optimizing) function could treat the grounded composition rather 
dynamically.

> About dynamic composition, it is the use of dynamic workflow, the use 
> of
> planning to compose,

Does it have to be planning? What about my replacement with equivalents 
above? (Or better, imagine something roughly equivalent to dynamic 
dispatch...I don't change the *workflow*, but I resolve the endpoint at 
run time. Is this really planning?)

>  the use of graphs. I mean that we don't know in
> advance which services will participate to the composition.

But that's true in the above case, at least in principle.

Also, in advance of *what*. The main point of a planning system is to 
decide what operators to use (in what order) *before* execution (i.e., 
off line). So, in a sense, after planning we DO know which services (we 
intend) to execute (in advance of execution).

What about contingent planning? E.g., if I have a conditional in my 
plan that's sensitive to some run time sensing. I can't say, in 
advance, which path will be taken, so I don't know what services will 
actually be executed. Contrariwise, if my planning domain has only a 
fixed set of operators (and I'm not allowed to change them), then I 
know what services could possibly be executed.

>  Moreover, if
> I have a service s1 that need another service s2 in order to be
> executed, so the dynamic composition should find this other service s2
> and put s2 in the composition. Isn't that? Do you have other examples 
> of
> dynamic compositions?

I'm not sure what purpose this distinction is to serve. So it's hard to 
figure out what falls on which side of the divide.

> So I want to hear from you what do you think about this classification
> and examples of static and dynamic compositions.

See above :)

Cheers,
Bijan.

Received on Wednesday, 12 April 2006 15:57:24 UTC