Service-oriented architecture (SOA) is a software development model that makes services reusable and lets them communicate across different platforms and languages to form new applications. It is an architectural style that focuses on discrete services instead of a monolithic design. In SOA, services use protocols that describe how they pass and parse messages using description metadata. This metadata describes both the functional characteristics of the service and quality-of-service characteristics.

SOA creates interoperability between apps and services, ensuring that existing applications can be easily scaled while simultaneously reducing costs related to the development of business service solutions. The defining concepts of SOA are business value, strategic goals, basic interoperability, shared services, and continuous improvement.

The basic principles of SOA include having a single business function per service, using multiple services to create a composite service for performing complex operations, and making functional building-blocks accessible over standard Internet protocols that are independent of platforms and programming languages.

SOA can be implemented with web services or microservices, which are used to make the functional building-blocks accessible over standard Internet protocols that are independent of platforms and programming languages.

The main components of SOA include services, service interfaces, service consumers, and service providers. Services are the basic building blocks of SOA, and they can be private or public. Service interfaces provide loose coupling, meaning they can be called with little or no knowledge of how the service is implemented underneath, reducing the dependencies between applications. Service consumers request information and send input data to the service, which processes the data, performs the task, and sends back a response. Service providers create web services and provide them to a service registry.

In summary, SOA is a software development model that makes services reusable and lets them communicate across different platforms and languages to form new applications. It creates interoperability between apps and services, ensuring that existing applications can be easily scaled while simultaneously reducing costs related to the development of business service solutions. SOA can be implemented with web services or microservices, and its main components include services, service interfaces, service consumers, and service providers.