Our Informal Definition of Service

A Service has a provider (or server) role and at least one consumer (or client) role where provider and consumer mean instantiations of these roles in the following specification:

• the service has a request signal, possibly containing some inputs, that should be made to a provider by a consumer,
• there is a way for the two parties (or agents) to have at least an implicit agreement prior to performance of the service,
• the agreement is that a provider, upon receipt of the request, performs or causes to be performed an action
• that changes the condition (or state) of
• something or someone designated by the consumer in the customer's request.