A service interface contract is a record of a service’s functions, parameters, data schema, protocols and security controls. The Enterprise Service Bus (ESB) Service Interface Contract Template documents service ownership and version and defines the context in which it should be used.
“A service is a logical representation of a repeatable activity that has a specified outcome. It is self-contained and is a ‘black box’ to its consumers.”
A service connected to the ESB can either be a service provider, requestor or event emitter. All can be considered services.
This document is aligned with the TOGAF definition of a service, and follows a service ontology.
 SOA Ontology Technical Standard : Service, ServiceContract, and ServiceInterface