How does GRA define a service interface?

GRA defines a service interface as "the means for interacting with a service." It includes the specific protocols, commands, and information exchange by which actions are initiated on the service. A service interface is what a system designer or implementer (programmer) uses to design or build executable software that interacts with the service. Since the service interface is the physical manifestation of the service, best practices call for a service interface which can be described in an open-standard, referenced format.