The service contract could be thought of as the go-between for the logic and the consumers of a given service. Thus, the service contract is an apt focal point for coupling a service since the service contract is what unites the different parts of a system. Without the service contract, the consumers and the logic will have a hard time communicating with one another.
The service contract typically creates a standard. It establishes a criteria to which other services must adhere to function in the system. While some might think a standardized system would present obstacles to an agile and mobile system, the opposite happens. A standardized system puts in place elements that make the various services adjustable, agile, and mobile. It’s almost like the service contract produces a living, breathing constitution that can seamlessly change with developing needs.
In business terms, adaptable service is referred to as “loose coupling.” As the name implies, “loose coupling” permits flexibility between the logic of a given system and the service contract. The breathing room lets outdated or glitching logic be replaced and improved without adversely impacting the people (“consumers”) who use the service.
If the consumer service was affected every time the logic was altered, the consumer experience would not be such a great one. However, with the service contract as the focal point, logic doesn’t need to determine or restrict the services, since the contract allows for the logic to be coupled to the contact so that the contract can lead the way.