Relationship of Semantic Web Services

Today I was reading a paper on Semantic Web Services titled "Semantic Web Services Composition Using AI planning of Description Logic" by Lirong Qiu, Fen Lin, Changlin Wan and Zhongzhi Shi. This paper explained in detail as how a Semantic Web Service works and also their composition using First Order Logic language. Below is some of the useful thing I found in that paper.

Relationship of Semantic Web Services:
There exists relationships between different Web Services when considered Service Composition. The Assumption is being made that Si and Sj is the sub-service of Services S. Both Si and Sj provide different kind of services. In light of that the relationship between Si and Sj can be identified as:

1. Independent Relationship: Si + Sj = Sj + Si which means each sub-service is independent of other and the order of execution of these two sub-services do not affect composition services.
2. Identical Relationship: Si = Sj, which means the two services seems to be doing the same thing but they have few differences in terms of their attributes.
3. Conditionally Identical Service: Si =~ Sj, this means Si can provide the same function as Sj in Some situations.
4. Substitute Relationship: Si (less than sign) Sj, which means Si and Sj can be substituted for each other or they can swap their roles anytime without affecting the overall functionality.
   
5. Conditionally Substitute Relationship: Si <= Sj, Which means Si and Sj can be substituted upon fulfilling some conditions.
6. Overlapping Relationship: Si (X) Sj, which means there is some commonality between the two services. While composing this overlapping or common part must be excluded.
7. Pre-Requisite Relationship: Si -> Sj, which means that one service has to finish before the other starts or in other words, the execution of Sj depends on successful completion of Si.

I am still working on how to make the Semantic Web Services automatic discoverable, while it is not easy but I guess it is not impossible too. With the advent of OWL-S it should be easy. I am yet to dig deep into it though.

Until Next Time.... :)