REpresentational State Transfer (REST) is a style of software architecture for distributed systems such as the World Wide Web. REST has emerged over the past few years as a predominant Web service design model. REST has increasingly displaced other design models such as SOAP and WSDL due to its simpler style.
The term representational state transfer was introduced and defined in 2000 by Roy Fielding in his doctoral dissertation. Fielding is one of the principal authors of the Hypertext Transfer Protocol (HTTP) specification versions 1.0 and 1.1.
The REST architectural style was developed in parallel with HTTP/1.1, based on the existing design of HTTP/1.0. The largest implementation of a system conforming to the REST architectural style is the World Wide Web. REST exemplifies how the Web's architecture emerged by characterizing and constraining the macro-interactions of the four components of the Web, namely origin servers, gateways, proxies and clients, without imposing limitations on the individual participants. As such, REST essentially governs the proper behavior of participants.
REST-style architectures consist of clients and servers. Clients initiate requests to servers; servers process requests and return appropriate responses. Requests and responses are built around the transfer of representations of resources. A resource can be essentially any coherent and meaningful concept that may be addressed. A representation of a resource is typically a document that captures the current or intended state of a resource.
The client begins sending requests when it is ready to make the transition to a new state. While one or more requests are outstanding, the client is considered to be in transition. The representation of each application state contains links that may be used the next time the client chooses to initiate a new state transition.
REST facilitates the transaction between web servers by allowing loose coupling between different services. REST is less strongly typed than its counterpart, SOAP. The REST language is based on the use of nouns and verbs, and has an emphasis on readability. Unlike SOAP, REST does not require XML parsing and does not require a message header to and from a service provider. This ultimately uses less bandwidth. REST error handling is also different from that used by SOAP. SOAP can have user defined error messages while REST requires the use of HTTP error handling.
Key goals Edit
Key goals of REST include:
REST has been applied to describe the desired web architecture, to help identify existing problems, to compare alternative solutions, and to ensure that protocol extensions would not violate the core constraints that make the Web successful.
Fielding describes REST's effect on scalability thus: Suleras:Quote
The REST architectural style describes the following six constraints applied to the architecture, while leaving the implementation of the individual components free to design:
The only optional constraint of REST architecture is code on demand. If a service violates any other constraint, it cannot strictly be considered RESTful.
Complying with these constraints, and thus conforming to the REST architectural style, will enable any kind of distributed hypermedia system to have desirable emergent properties, such as performance, scalability, simplicity, modifiability, visibility, portability and reliability.
Representational State Transfer is intended to evoke an image of how a well-designed Web application behaves: Presented with a network of Web pages (a virtual state-machine), the user progresses through an application by selecting links (state transitions), resulting in the next page (representing the next state of the application) being transferred to the user and rendered for their use. Fielding's PhD thesis, section 6.1
REST was initially described in the context of HTTP, but it is not limited to that protocol. RESTful architectures may be based on other Application Layer protocols if they already provide a rich and uniform vocabulary for applications based on the transfer of meaningful representational state. RESTful applications maximize the use of the existing, well-defined interface and other built-in capabilities provided by the chosen network protocol, and minimize the addition of new application-specific features on top of it.
Vocabulary re-use vs. its arbitrary extension: HTTP and SOAP Edit
REST utilizes these verbs and other existing features of the well-known, well-defined HTTP protocol. For example, layered proxy and gateway components perform additional functions on the network, such as HTTP caching and security enforcement.
This additive, "re-invention of the wheel" vocabulary — defined on the spot and subject to individual judgment or preference — disregards many of HTTP's existing capabilities, such as authentication, caching, and content-type negotiation. The advantage of SOAP over REST comes from this same limitation: Since it does not take advantage of HTTP conventions, SOAP works equally well over raw TCP, named pipes, message queues, etc.
Guiding principles of the interface Suleras:Anchor Edit
The uniform interface that any REST interface must provide is considered fundamental to the design of any REST service.
Central principle Edit
An important concept in REST is the existence of resources (sources of specific information), each of which is referenced with a global identifier (e.g., a URI in HTTP). In order to manipulate these resources, components of the network (user agents and origin servers) communicate via a standardized interface (e.g., HTTP) and exchange representations of these resources (the actual documents conveying the information). For example, a resource that represents a circle (as a logical object) may accept and return a representation that specifies a center point and radius, formatted in SVG, but may also accept and return a representation that specifies any three distinct points along the curve (since this also uniquely identifies a circle) as a comma-separated list.
Any number of connectors (e.g., clients, servers, caches, tunnels, etc.) can mediate the request, but each does so without "seeing past" its own request (referred to as "layering," another constraint of REST and a common principle in many other parts of information and networking architecture). Thus, an application can interact with a resource by knowing two things: the identifier of the resource and the action required—it does not need to know whether there are caches, proxies, gateways, firewalls, tunnels, or anything else between it and the server actually holding the information. The application does, however, need to understand the format of the information (representation) returned, which is typically an HTML, XML or JSON document of some kind, although it may be an image, plain text, or any other content.
RESTful web services Edit
A RESTful web service (also called a RESTful web API) is a web service implemented using HTTP and the principles of REST. It is a collection of resources, with four defined aspects:
The following table shows how the HTTP methods are typically used to implement a web service.
Unlike SOAP-based web services, there is no "official" standard for RESTful web services. This is because REST is an architecture, unlike SOAP, which is a protocol. Even though REST is not a standard, a RESTful implementation such as the Web can use standards like HTTP, URI, XML, etc.
Outside the Web Edit
Software that may interact with a number of different kinds of objects or devices can do so by virtue of a uniform, agreed interface.
The Common Management Information Protocol (CMIP) was designed to allow the control of network resources by presenting their manageable characteristics as object attributes. The objects have parent-child relationships that are identified using distinguished names and attributes, which are read and modified by a set of CRUD operations. The notable non-restful aspect of CMIP is the M_ACTION operation although, wherever possible, designers of management information bases (MIBs) would typically endeavour to represent controllable and stateful aspects of network equipment through attributes.
REST can be found in a number of places on the public Web:
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