An Introduction to Services From This Coder's Perspective

First, there is the question of “what is a Service?”  

W3C defines a web service as:
a software system designed to support interoperable machine-to-machine interaction over a network.”[1]

They go on to specify some specific technologies mandated by this particular standard and the role a service plays:
“The purpose of a Web service is to provide some functionality on behalf of its owner -- a person or organization."
This definition describes the infrastructure, focusing on how we deploy services and what purpose they serve right now to MBAs.  It is as though they are defining a program as "a sequence of machine instructions that perform mathematical or logical operations on behalf of a computer operator”.  I want a definition that tells me how to address the technical questions that emerge and provides guidance on how we will be writing and employing services going forward.  My current personal definition is:
A Service is an Object bound at run-time by a networking protocol.

Note that I mean “object” here under Alan Kay’s definition [2] and not in the particular sense that the word is used any specific language like Java or C++.  Despite varying dynamics, all service frameworks encapsulate some combination of data and behavior (not necessarily *well*, of course, but when they fail it is usually clear from the pain that follows.)  They hide implementation details while fulfilling either implicit or explicit contracts in response to messages sent by other services.[3]

The interesting change from current Object-Oriented programming paradigms is that they also encapsulate the location they are executing and the provider of the object.  Because we bind to the specific implementation at runtime using a networking protocol of some kind, the object can be running on any machine, virtual or physical, anywhere reachable by that protocol.  I don’t think this fundamentally changes the paradigm any more than dynamically linked libraries did, but it is really, really cool.