Explicit / implicit ? = confused.

Hello!

I have been trying different tools for OWL-S and learnt the language/syntax,
but I am missing out on a few fundamental details: 

 

How are web services supposed to be found by semantic matching
(capability-based matching) of descriptions written in OWL-S? All
descriptions describe what a web service really does implicitly, so you are
supposed to be able to infer what a service does by looking at the inputs
and outputs, right? But what happens if you have a trivial calculator
service that adds two numbers into a sum. Inputs can then be two “Integer”s
and output can also be an “Integer”. But what distinguished this service
from another calculator service that subtracts, multiplies or divides
instead? Or from a coordinate transformation service that maps from two
dimensions to one? Are preconditions and effects supposed to enable this
kind of distinguishing? Or do you also have to annotate each service
explicitly by calling it “Calculator_Add”, “Calculator_Subtract” etc? It
seems to me that somehow a service has to be distinguished by explicitly
annotating the service itself, the conditions and effects or the inputs and
outputs.

 

Confused but still grateful for an explanation :-)

 

Martin Gülich