A Service: It has the methods with the defined contracts and the implementation of the business logic to connect the DB or other service.
A Service Repository: The service repository provides a home for the services and the service bus provides an industry-standard mechanism for connecting to and interacting with the services. SOA is thinking, it's an architectural concept and web service is one of the technical approach to complete it.
WCF is a runtime and a set of APIs for creating systems that sends messages between services and clients.
Operation Contract Attribute: It can only be applied on methods.
It is used to declare methods which belong to a Service Contract.
It also shows the formal agreements between client and service to define a platform-neutral and standard for describing that what the service does.
Service Contract: A service contract defines the operations which are exposed by the service to the outside world.
We must say that it defines the operations that a service will perform when executed.
It tells more things about a service, like message data types, operation locations, the protocols the client will need in order to communicate with the service.But WCF services are accessible with different protocols like http, tcp, msmq, etc.A few sample scenarios include: For more details visit the following link: Answer Windows Communication Foundation (WCF) is a framework for building service-oriented applications by which we can send asynchronous message/data from one service endpoint to another service endpoint.It controls the service description and message formats.For more details visit the following link: Answer: The main use of contracts is to allow the client and services agree as to the types of operations and structures they will use during the communication process.To create a service contract you define an interface with related methods representative of a collection of service operations, and then decorate the interface/class with the Service Contract Attribute to indicate it is a service contract.