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Application Programming Interface (API)
An Application Programming Interface (API) contains software building tools, subroutine definitions, and communication protocols that facilitate interaction between systems. An API may be for a database system, operating system, computer hardware, or a web-based system.
An API makes it simpler for programmers to use certain technologies to build applications. APIs can include specifications for data structures, variables, routines, object classes, remote calls, and more.
Types of APIs
| Type | Description | Examples |
|---|---|---|
| Operating System APIs | Interface between OS and applications | POSIX, Windows API |
| Library APIs | Access to software library functions | Standard C Library, Java API |
| Web APIs | HTTP-based interfaces for web services | REST APIs, GraphQL |
| Remote APIs | Interact with remote resources over network | RPC, Web Services |
Uses of Application Programming Interfaces
Operating Systems
The interface between an operating system and an application is specified with an API. For example, POSIX has APIs that can convert an application written for one POSIX operating system to one that can be used on another POSIX operating system.
Libraries and Frameworks
Often APIs are related to software libraries. The API describes the behavior of the system while the libraries actually implement that behavior. A single API can have multiple libraries as it can have many different implementations. Sometimes, an API can be linked to a software framework as well.
Web APIs
The application programming interfaces for web servers or web browsers are known as web APIs. These web APIs can be server-side or client-side.
Server-side web APIs have an interface that contains endpoints which lead to request-response message systems that are written in JSON or XML. Most of this is achieved using an HTTP web server. Client-side web APIs are used to extend the functionality of a web browser.
Remote APIs
The remote application programming interfaces allow programmers to manipulate remote resources. Most remote APIs are required to maintain object abstraction in object-oriented programming. This can be done by executing a method call locally which then invokes the corresponding method call on a remote object and gets the result locally as a return value.
API Release Policies
The policies for releasing APIs are private, partner, and public. Details about these are given as follows −
| Policy Type | Access Level | Use Cases |
|---|---|---|
| Private APIs | Internal company use only | Internal microservices, backend systems |
| Partner APIs | Company and business partners | B2B integrations, controlled third-party access |
| Public APIs | Freely available to all developers | Microsoft Windows API, Apple's Cocoa API |
Key Benefits
Standardization − Provides consistent interface for accessing services
Abstraction − Hides complex implementation details from developers
Reusability − Allows code reuse across different applications
Modularity − Enables building applications with independent components
Conclusion
APIs serve as crucial intermediaries that enable different software systems to communicate and interact seamlessly. They provide standardized interfaces that simplify development, promote code reuse, and enable the creation of complex applications through modular design. Understanding API types and release policies is essential for effective system integration.
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