REST has been employed throughout the software industry to create stateless, reliable web-based applications. An application that adheres to the REST architectural constraints may be informally described as RESTful, although this term is more commonly associated with the design of HTTP-based APIs and what are widely considered best practices regarding the "verbs" (HTTP methods) a resource responds to while having little to do with REST as originally formulated—and is often even at odds with the concept.[2]
The term representational state transfer was introduced and defined in 2000 by computer scientist Roy Fielding in his doctoral dissertation. It means that a server will respond with the representation of a resource (today, it will most often be an HTML, XMLorJSON document) and that resource will contain hypermedia links that can be followed to make the state of the system change. Any such request will in turn receive the representation of a resource, and so on.
An important consequence is that the only identifier that needs to be known is the identifier of the first resource requested, and all other identifiers will be discovered. This means that those identifiers can change without the need to inform the client beforehand and that there can be only loose coupling between client and server.
The Web began to enter everyday use in 1993–1994, when websites for general use started to become available.[3] At the time, there was only a fragmented description of the Web's architecture, and there was pressure in the industry to agree on some standard for the Web interface protocols. For instance, several experimental extensions had been added to the communication protocol (HTTP) to support proxies, and more extensions were being proposed, but there was a need for a formal Web architecture with which to evaluate the impact of these changes.[4]
The W3C and IETFworking groups together started work on creating formal descriptions of the Web's three primary standards: URI, HTTP, and HTML. Roy Fielding was involved in the creation of these standards (specifically HTTP 1.0 and 1.1, and URI), and during the next six years he created the REST architectural style, testing its constraints on the Web's protocol standards and using it as a means to define architectural improvements — and to identify architectural mismatches. Fielding defined REST in his 2000 PhD dissertation "Architectural Styles and the Design of Network-based Software Architectures"[1][5]atUC Irvine.
To create the REST architectural style, Fielding identified the requirements that apply when creating a world-wide network-based application, such as the need for a low entry barrier to enable global adoption. He also surveyed many existing architectural styles for network-based applications, identifying which features are shared with other styles, such as caching and client–server features, and those which are unique to REST, such as the concept of resources. Fielding was trying to both categorise the existing architecture of the current implementation and identify which aspects should be considered central to the behavioural and performance requirements of the Web.
By their nature, architectural styles are independent of any specific implementation, and while REST was created as part of the development of the Web standards, the implementation of the Web does not obey every constraint in the REST architectural style. Mismatches can occur due to ignorance or oversight, but the existence of the REST architectural style means that they can be identified before they become standardised. For example, Fielding identified the embedding of session information in URIs as a violation of the constraints of REST which can negatively affect shared caching and server scalability. HTTP cookies also violated REST constraints because they can become out of sync with the browser's application state, making them unreliable; they also contain opaque data that can be a concern for privacy and security.
The REST architectural style is designed for network-based applications, specifically client-server applications. But more than that, it is designed for Internet-scale usage, so the coupling between the user agent (client) and the origin server must be as loose as possible to facilitate large-scale adoption.
The strong decoupling of client and server together with the text-based transfer of information using a uniform addressing protocol provided the basis for meeting the requirements of the Web: extensibility, anarchic scalability and independent deployment of components, large-grain data transfer, and a low entry-barrier for content readers, content authors and developers alike.
The REST architectural style defines six guiding constraints.[6][8] When these constraints are applied to the system architecture, it gains desirable non-functional properties, such as performance, scalability, simplicity, modifiability, visibility, portability, and reliability.[1]
Client/Server - Client are separated from servers by a well-defined interface
Stateless - A specific client does not consume server storage when it is "at rest"
Cache - Responses indicate their own cacheability
Uniform Interface
Layered System - A client cannot ordinarily tell whether it is connected directly to the end server, or to an intermediary along the way
Code on Demand (optional) - Servers are able to temporarily extend or customize the functionality of a client by transferring logic to the client that can be executed within a standard virtual machine
The uniform interface constraint is fundamental to the design of any RESTful system.[1] It simplifies and decouples the architecture, which enables each part to evolve independently. The four constraints for this uniform interface are:
Resource identification in requests: Individual resources are identified in requests using URIs. The resources themselves are conceptually separate from the representations that are returned to the client. For example, the server could send data from its database as HTML, XML or as JSON—none of which are the server's internal representation.
Resource manipulation through representations: When a client holds a representation of a resource, including any metadata attached, it has enough information to modify or delete the resource's state.
Self-descriptive messages: Each message includes enough information to describe how to process the message. For example, which parser to invoke can be specified by a media type.[1]
Hypermedia as the engine of application state (HATEOAS) - Having accessed an initial URI for the REST application—analogous to a human Web user accessing the home page of a website—a REST client should then be able to use server-provided links dynamically to discover all the available resources it needs. As access proceeds, the server responds with text that includes hyperlinks to other resources that are currently available. There is no need for the client to be hard-coded with information regarding the structure of the server.[10]
^ abcdefFielding, Roy Thomas (2000). "Chapter 5: Representational State Transfer (REST)". Architectural Styles and the Design of Network-based Software Architectures (Ph.D.). University of California, Irvine. Archived from the original on 2021-05-13. Retrieved 2004-08-17.
^Fielding, Roy Thomas (2000). "Chapter 6: Experience and Evaluation". Architectural Styles and the Design of Network-based Software Architectures (Ph.D.). University of California, Irvine. Archived from the original on 2023-03-26. Retrieved 2023-06-21.
^ abErl, Thomas; Carlyle, Benjamin; Pautasso, Cesare; Balasubramanian, Raj (2012). "5.1". SOA with REST: Principles, Patterns & Constraints for Building Enterprise Solutions with REST. Upper Saddle River, New Jersey: Prentice Hall. ISBN978-0-13-701251-0.
^ abFielding, Roy Thomas (2000). "Chapter 2: Network-based Application Architectures". Architectural Styles and the Design of Network-based Software Architectures (Ph.D.). University of California, Irvine. Archived from the original on 2014-12-16. Retrieved 2014-04-12.
^Ivan Salvadori, Frank Siqueira (June 2015). "A Maturity Model for Semantic RESTful Web APIs". Conference: Web Services (ICWS), 2015 IEEE International Conference OnAt. New York. Archived from the original on 2024-02-27. Retrieved 2020-12-14 – via Researchgate.
