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Application programming interface

(also API)

Application programming interface definition

An application programming interface (API) is a set of rules and protocols that allows different software applications to communicate, interact, and share data. With API, developers can use the functionality of existing software components or services without having to build everything from scratch.

See also: interface message processor

Four main types of web APIs

  • Public APIs. Public APIs are open-source and can be used by any developers and businesses. They typically have moderate authorization and authentication.
  • Partner APIs. Partner APIs are only available to selected and authenticated outside developers and consumers. These APIs are typically used to facilitate business-to-business (B2B) activities.
  • Internal APIs. Internal APIs are also known as private APIs. These APIs are only used within a specific organization to connect data and systems. For example, an internal API may connect an organization’s HR and payroll systems.
  • Composite APIs. Composite APIs typically combine the data and functionalities from several APIs into a single interface. These APIs bring together various functionalities to provide a more unified experience for developers.

How an API works

APIs work by defining a set of rules and protocols that regulate how different software systems can communicate and interact with each other. Let’s briefly review the steps involved:

  • A client application talks to an API by sending a request that includes specific instructions and information.
  • The API verifies the request and checks that it has the correct permissions.
  • The API can connect to other systems to get or change information as needed.
  • After the API finishes processing the request, it sends a message back to the client application.
  • The response is organized in a specific way, like putting it in a box with a clear label, so the client application knows how to understand it.
  • If something goes wrong, the API will inform the client application by sending an error message or signal that something didn't work properly.