RE: OWL-S Composition using Multiple Partners

 

> -----Original Message-----
> From: public-sws-ig-request@w3.org 
> [mailto:public-sws-ig-request@w3.org] On Behalf Of rajesh k
> Sent: 14 March 2006 18:27
> To: public-sws-ig@w3.org
> Cc: rajk_cs@hotmail.com
> Subject: OWL-S Composition using Multiple Partners
> 
> 
> Hi,
> 
> I am trying to work on an example to compose services using 
> OWL-S. I am using the OWL-S editor of SRI for OWL-S services 
> creation. I have a few clarifications regarding the 
> composition that can be done with OWL-S.
>

There has always been disagreement in the community about exactly what
kind of composition OWL-S describes. I'm sure that everyone that replies
to this message will have a different opinion. It is precisely because
OWL-S lacks a formal semantics (something that SWSF
http://www.w3.org/Submission/2005/07/ looks at) that this continues to
be a problem.

> I understand that OWL-S is an orchestration language like 
> BPEL and it cannot support choreography [1]. 

One difficulty here is that the word 'choreography' is used in many
ways. The view from the W3C is that a choreography describes a
multi-party interaction, as distinct from an orchestration which defines
the way one party invokes other services. From this perspective OWL-S
does not describe choreography in general. It really only describes the
conversation between a client and a single service. I regard a
conversation as a special case of choreography where interactions with
other parties have been elided.

But neither does OWL-S fully describe an orchestration, at least not in
the sense that you can execute it in the way you can execute BPEL. OWL-S
allows partial (ie. non-algorithmic) description of a conversation, and
can be viewed as describing a set of process constraints (that a BPEL or
some other executable should conform to). 

> But in the case 
> of BPEL the services are combined from partner services to 
> form a composition, but I am not sure how this could be done 
> with OWL-S. 

Here I agree with [1] that OWL-S (at least the process model) does not
describe service composition, but process composition. Of course it's
possible to describe a process composition where each operation happens
to have a different end-point (as defined in the grounding of each
atomic process) and that these end-points just happen to belong to
different service providers. This may be good enough to invoke the
operations in the correct order. My argument with this is, does this
adequately describe the _service_ composition? For example, where in the
process model can we describe which service each atomic process is
associated with? And where is the composition of the services (as
opposed to the processes) themselves described?

...

> Please also let me know about composition examples involving 
> multiple providers and if possible please provide me the 
> pointers for them.
>

"Semi-automatic Composition of Web Services using Semantic Descriptions"
by Evren Sirin, James Hendler and Bijan Parsia is well worth a read.

Steve.


> [1] Barry Norton, Experiences with OWL-S, Directions for Service
> Composition: The Cashew Position, In OWL: Experiences and 
> Directions Workshop (OWLED 2005), co-located with ISWC 2005.
> 
> [2] Biplav Srivastava and J. Koehler, Planning with Workflows 
> - An Emerging Paradigm for Web Services Composition,  In 
> ICAPS 2004 Workshop on Planning and Scheduling for Grid and 
> Web Services, Whistler, British Columbia, Canada, June 2004.

Received on Wednesday, 15 March 2006 15:12:30 UTC