What is SOA? – Service-Oriented Architecture Explained – AWS

Services are the basic building blocks of SOA. They can be private—available only to internal users of an organization—or public—accessible over the internet to all. Individually, each service has three main features.

Service implementation
The service implementation is the code that builds the logic for performing the specific service function, such as user authentication or bill calculation.

Service contract

The service contract defines the nature of the service and its associated terms and conditions, such as the prerequisites for using the service, service cost, and quality of service provided.

Service interface

In SOA, other services or systems communicate with a service through its service interface. The interface defines how you can invoke the service to perform activities or exchange data. It reduces dependencies between services and the service requester. For example, even users with little or no understanding of the underlying code logic can use a service through its interface.