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.
Conforming to the REST constraints is generally referred to as being "RESTful".Contents [hide] 1 About 2 Key goals 3 Constraints 4 Concept 4.1 Vocabulary Re-Use vs. Its Arbitrary Extension: HTTP and SOAP 5 Guiding principles of the interface 6 Central principle 7 RESTful web services 8 Outside the Web 8.1 CMIP 9 Footnotes 10 See also 10.1 Public implementations 10.2 Framework implementations 11 References 12 External links
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 off the use of nouns and verbs, and has an emphasis on readability. Unlike SOAP, REST does not require XML parsing and doesn't require a message header to and from a service provider. This ultimately uses less bandwidth. REST is also different from SOAP in that error handling is different between the two. SOAP can have user defined error messages while REST requires the use of HTTP error handling. REST also only support synchronous (in contrast to asynchronous) messaging, because of its reliance on HTTP and HTTPS infrastructure. This increases the number of threads in use by a REST web service.  Key goals
Key goals of REST include: Scalability of component interactions Generality of interfaces Independent deployment of components Intermediary components to reduce latency, enforce security and encapsulate legacy systems
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: REST's client–server separation of concerns simplifies component implementation, reduces the complexity of connector semantics, improves the effectiveness of performance tuning, and increases the scalability of pure server components. Layered system constraints allow intermediaries—proxies, gateways, and firewalls—to be introduced at various points in the communication without changing the interfaces between components, thus allowing them to assist in communication translation or improve performance via large-scale, shared caching. REST enables intermediate processing by constraining messages to be self-descriptive: interaction is stateless between requests, standard methods and media types are used to indicate semantics and exchange information, and responses explicitly indicate cacheability.  Constraints
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.  Concept
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 his 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
In addition to URIs; Internet media types; request and response codes; etc., HTTP has a rich vocabulary of verbs: GET POST PUT etc.
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.
SOAP RPC over HTTP, on the other hand, encourages each application designer to define new and arbitrary verbs that supplant HTTP verbs: getUsers() getNewUsersSince(date SinceDate) savePurchaseOrder(string CustomerID, string PurchaseOrderID) etc.
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. The neutrality of this article is disputed. Please see the discussion on the talk page. Please do not remove this message until the dispute is resolved. (April 2012)
 Guiding principles of the interface
The uniform interface that any REST interface must provide is considered fundamental to the design of any REST service. Identification of resources Individual resources are identified in requests, for example using URIs in web-based REST systems. The resources themselves are conceptually separate from the representations that are returned to the client. For example, the server does not send its database, but rather, perhaps, some HTML, XML or JSON that represents some database records expressed, for instance, in Finnish and encoded in UTF-8, depending on the details of the request and the server implementation. Manipulation of resources through these representations When a client holds a representation of a resource, including any metadata attached, it has enough information to modify or delete the resource on the server, provided it has permission to do so. Self-descriptive messages Each message includes enough information to describe how to process the message. For example, which parser to invoke may be specified by an Internet media type (previously known as a MIME type). Responses also explicitly indicate their cacheability. Hypermedia as the engine of application state Clients make state transitions only through actions that are dynamically identified within hypermedia by the server (e.g. by hyperlinks within hypertext). Except for simple fixed entry points to the application, a client does not assume that any particular actions will be available for any particular resources beyond those described in representations previously received from the server.  Central principle
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
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 base URI for the web service, such as http://example.com/resources/ the Internet media type of the data supported by the web service. This is often JSON, XML or YAML but can be any other valid Internet media type. the set of operations supported by the web service using HTTP methods (e.g., GET, PUT, POST, or DELETE). The API must be hypertext driven.
The following table shows how the HTTP methods are typically used to implement a web service. RESTful Web Service HTTP methodsResource GET PUT POST DELETE Collection URI, such as http://example.com/resources/ List the URIs and perhaps other details of the collection's members. Replace the entire collection with another collection. Create a new entry in the collection. The new entry's URL is assigned automatically and is usually returned by the operation. Delete the entire collection. Element URI, such as http://example.com/resources/item17 Retrieve a representation of the addressed member of the collection, expressed in an appropriate Internet media type. Replace the addressed member of the collection, or if it doesn't exist, create it. Treat the addressed member as a collection in its own right and create a new entry in it. Delete the addressed member of the collection.
The PUT and DELETE methods are idempotent methods. The GET method is a safe method (or nullipotent), meaning that calling it produces no side-effects.
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
Software that may interact with a number of different kinds of objects or devices can do so by virtue of a uniform, agreed interface.  CMIP
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.  Footnotes ^ http://www.ibm.com/developerworks/webservices/library/ws-restful/ IBM Developerworks page REST ^ a b Chapter 5 of Fielding's dissertation is "Representational State Transfer (REST)". ^ "Fielding discussing the definition of the REST term" ^ RFC 1945 ^ RFC 2616 ^ Richardson, Leonard; Sam Ruby (2007). "Preface". RESTful web service. O'Reilly Media. ISBN 978-0-596-52926-0. Retrieved 18 January 2011. ^ Fielding discusses the development of the REST style ^ Fielding talks about application states ^ http://www.youtube.com/watch?v=v3OMEAU_4HI SOAP vs REST - Youtube video ^ (Fielding 2000, §5.3.1) ^ Scribner, Kenn; Seely, Scott (2009), Effective REST Services via .NET, Boston: Addison-Wesley, ISBN 978-0-321-61325-7 ^ (Fielding 2000, §5.1.5) ^ REST APIs must be hypertext driven by Roy Fielding ^ Richardson, Leonard; Ruby, Sam (2007), RESTful Web Services, O'Reilly (published (May 8, 2007)), ISBN 0-596-52926-0 ^ Elkstein, M. What is REST?. Retrieved on 2009-07-04.  See also Clean URLs Create, read, update and delete (CRUD) HATEOAS (Hypermedia as the Engine of Application State) Service-oriented architecture  Public implementations
REST can be found in a number of places on the public Web: The Atom Publishing Protocol for publishing to blogs is considered a canonical RESTful protocol. Sun Microsystems' Cloud API is a good example of resource media type documentation. The Open Services for Lifecycle Collaboration (OSLC) initiative is establishing a RESTful approach to integrating software development artifacts. CouchDB is a document-oriented database written in Erlang that provides a RESTful JSON API that can be accessed from any environment that allows HTTP requests. MySQL Cluster is a write-scalable auto-sharded database also accessible through a native REST/JSON interface as an Apache module. Microsoft's Canonical REST Entity Service. Nuxeo, an open source document manager, implements a Content Automation interface via a REST API Sones GraphDB is a graph-oriented database written in C# that provides a RESTful interface  Framework implementations It has been suggested that this article or section be merged into List of web service frameworks. (Discuss) Proposed since March 2012.
This audio file was created from a revision of the "Representational state transfer" article dated 2011-11-25, and does not reflect subsequent edits to the article. (Audio help) More spoken articles
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