difference between data contract and the service contract

As a programmer, I sometimes am at a loss of words trying to articulate the concept of this "thingy" on the Internets that accepts some junk and does something with the junk and the junk flows through different thingies until it hits the end and ...

Just to be clear, my above line was used to accentuate how difficult it is to describe a web service to a business person.  Recently, I was reading up on WCF on the microsoft site and came across a very helpful paragraph that describes the difference between service and data contracts.

http://msdn.microsoft.com/en-us/library/aa480190.aspx

From microsoft:
The split between the data contract and the service contract is important. Service contracts typically define a logically and semantically related set of operations grouped on an interface and are about how a service behaves. The data contract defined information items that you flow across service boundaries and that are handled with additional logic on the provider and consumer side. If you were looking at it from a (English language) grammar perspective, you could consider operations to be the predicates and the data that flows are the objects, while the caller is the subject. Subjects can do a lot with objects. Every "do" is an operation.