A RESTful API is an interface used by two computer systems to securely exchange information over the Internet. Most business applications need to communicate with other internal and third-party applications to perform various tasks. For example, to generate monthly payroll, your internal accounting system must communicate with your client’s banking system to automate billing and interact with your internal timekeeping application. RESTful APIs support this information exchange because they follow secure, reliable, and efficient standards for programmatic communication.
What is an API?
An application programming interface (API) defines the rules that must be followed to communicate with other software systems. Developers implement or create APIs so that other applications can programmatically interact with their applications. For example, a timesheet application contains an API that requests the employee’s full name and date range. Upon receiving this information, the interface internally processes the employee’s timesheet and returns the number of hours worked during the specified period.
In this way, the network API functions as a gateway between clients and resources on the Internet.
Clients
Clients are users who want to access information on the Internet. A client can be a person or a software system that uses an API. For example, developers can create programs that access weather data from a weather system. You can also access this data from a browser by visiting a website with weather information.
Resources
Resources are the information that different applications provide to their clients. Resources can be images, videos, text, numbers, or any type of data. A computer that provides resources to a client is also called a server. APIs allow organizations to share resources and provide web services by providing security, control, and authentication. In addition, APIs help determine which clients can access certain internal resources.
What is REST?
Representational State Transfer (REST) is a software architecture that defines the environment in which an API operates. REST was originally created as a guideline for managing interactions on a complex network such as the Internet. A REST-based architecture can be used to support high-performance and reliable communication at the scale required. It can be easily implemented and modified, providing transparency and cross-platform portability to any API system.
Developers can create APIs using multiple architectures. APIs that conform to the REST architectural style are called REST APIs. Web services that implement the REST architecture are called RESTful web services. Generally, the term RESTful APIs refers to network-based RESTful APIs. However, REST API and RESTful API are interchangeable terms.
The following are some principles of the REST architectural style:
Unified Interface
A unified interface is the structural foundation of any RESTful web service. It indicates that the server communicates information in a standardized format. The formatted resource in REST is called a representation. This format may differ from the internal representation of the resource in the server application. For example, a server may store data as text but send it in an HTML representation format.
A single interface imposes four architectural constraints:
- Queries must identify resources. This is accomplished through a single resource identifier.
- Clients have enough information in the resource representation to modify or delete the resource if desired. The server fulfills this condition by sending metadata that further describes the resource.
- Clients receive information about further processing of the views. The server implements this by sending descriptive messages that contain metadata about how the client can make optimal use of them.
- Clients receive information about all related resources needed to accomplish the task. The server implements this by sending hyperlinks in the view so that clients can dynamically discover more resources.
Lack of state persistence
In the REST architecture, no state persistence refers to a communication method in which the server executes each client request independently of all previous requests. Clients can request resources in any order, and each request is either isolated from other requests or its state is not preserved. This design limitation of the REST API implies that the server can fully understand and fulfill the request each time.
Tiered system
In a tiered system architecture, a client can connect to other authorized intermediaries between the client and server and still receive responses from the server. Servers can also pass requests to other servers. You can design your RESTful Web service to run on multiple servers with multiple layers (security, application, and business logic) sharing client requests. These layers remain invisible to the client.
Cache Capacity
RESTful web services support caching, which is the process of storing some responses on the client or on an intermediary to reduce server response time. For example, you visit a Web site with generic header and footer images on each page. Each time you visit a new page of the website, the server must resend the same images. To avoid this, the client caches or stores these images after the first response and then uses the images from the cache. RESTful web services manage caching by using API responses that define themselves as cacheable or non-cacheable.
Code on Demand
In an architectural style, REST servers can temporarily extend or customize client functionality by passing software code. For example, when you fill out a registration form on a website, your browser will immediately highlight any errors made (such as incorrect phone numbers). This happens thanks to the code sent by the server.