Representational state transfer is an abstraction of the architecture of the World Wide Web.
More precisely, REST is an architectural style consisting of a coordinated set of architectural
constraints applied to components, connectors, and data elements, within a distributed hypermedia
system. REST ignores the details of component implementation and protocol syntax in order
to focus on the roles of components, the constraints upon their interaction with other components,
and their interpretation of significant data elements.
The term representational state transfer was introduced and defined in 2000 by Roy Fielding
in his doctoral dissertation at UC Irvine. REST has been applied to describe desired
web architecture, to 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 used REST to design HTTP 1.1 and Uniform Resource Identifiers.
The REST architectural style is also applied to the development of web services as an alternative
to other distributed-computing specifications such as SOAP. One can characterise web services
as "RESTful" if they conform to the constraints described in the Architectural constraints
section. See the Applied to web services section if you are only interested in the application
of REST to web APIs.
History The REST architectural style was developed
by W3C Technical Architecture Group in parallel with HTTP 1.1, based on the existing design
of HTTP 1.0. The World Wide Web represents the largest implementation of a system conforming
to the REST architectural style. Software architecture
A software architecture is defined by a configuration of components, connectors, and data constrained
in their relationships in order to achieve a desired set of architectural properties.
Components A component is an abstract unit of software
instructions and internal state that provides a transformation of data via its interface.
Connectors A connector is an abstract mechanism that
mediates communication, coordination, or cooperation among components.
Data Data is an element of information that is
transferred from a component, or received by a component, via a connector.
Architectural properties The architectural properties induced by the
architectural constraints of the REST architectural style are:
Performance - component interactions can be the dominant factor in user-perceived performance
and network efficiency. Scalability to support large numbers of components
and interactions among components 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.
Simplicity of interfaces Modifiability of components to meet changing
needs Visibility of communication between components
by service agents Portability of components by moving program
code with the data Reliability is the resistance to failure at
the system level in the presence of failures within components, connectors, or data
Architectural constraints The architectural properties of REST are realized
by applying specific interaction constraints to components, connectors, and data elements.
The formal REST constraints are: Client–server
A uniform interface separates clients from servers. This separation of concerns means
that, for example, clients are not concerned with data storage, which remains internal
to each server, so that the portability of client code is improved. Servers are not concerned
with the user interface or user state, so that servers can be simpler and more scalable.
Servers and clients may also be replaced and developed independently, as long as the interface
between them is not altered. Stateless
The client–server communication is further constrained by no client context being stored
on the server between requests. Each request from any client contains all the information
necessary to service the request, and session state is held in the client. Important to
note is that the session state can be transferred by the server to another service such as a
database to maintain a persistent state for a period and allow authentication. 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. Cacheable
As on the World Wide Web, clients can cache responses. Responses must therefore, implicitly
or explicitly, define themselves as cacheable, or not, to prevent clients reusing state or
inappropriate data in response to further requests. Well-managed caching partially or
completely eliminates some client–server interactions, further improving scalability
and performance. Layered system
A client cannot ordinarily tell whether it is connected directly to the end server, or
to an intermediary along the way. Intermediary servers may improve system scalability by
enabling load-balancing and by providing shared caches. They may also enforce security policies.
Code on demand
Servers can temporarily extend or customize the functionality of a client by the transfer
of executable code. Examples of this may include compiled components such as Java applets and
client-side scripts such as JavaScript. "Code on demand" is the only optional constraint
of the REST architecture. Uniform interface
The uniform interface constraint is fundamental to the design of any REST service. The uniform
interface simplifies and decouples the architecture, which enables each part to evolve independently.
The four guiding principles of this interface are:
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.
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. 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. 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. Except for simple fixed entry points to the application, a client
does not assume that any particular action is available for any particular resources
beyond those described in representations previously received from the server.
One can characterise applications conforming to the REST constraints described in this
section as "RESTful". If a service violates any of the required constraints, it cannot
be considered RESTful. Complying with these constraints, and thus
conforming to the REST architectural-style, enables 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, the user progresses through an application by selecting links, resulting
in the next page being transferred to the user and rendered for their use.
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.
Applied to web services Web service APIs that adhere to the Architectural
constraints are called RESTful. HTTP based RESTful APIs are defined with these aspects:
base URI, such as http:example.com an Internet media type for the data. This
is often JSON but can be any other valid Internet media type
standard HTTP methods hypertext links to reference state
hypertext links to reference related resources The following table shows the HTTP methods
that are typically used to implement a RESTful API.
The PUT and DELETE methods are referred to as idempotent, meaning that the operation
will produce the same result no matter how many times it is repeated. The GET method
is a safe method, meaning that calling it produces no side-effects. In other words,
retrieving or accessing a record doesn't change it.
Unlike SOAP-based web services, there is no "official" standard for RESTful web APIs.
This is because REST is an architectural style, 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. See also
RSDL Clean URLs
Sinatra Create, read, update and delete
Resource-oriented architecture Service-oriented architecture
Resource-oriented computing Domain Application Protocol
RAML Swagger Specification for defining interfaces
References Fielding, Roy T.; Taylor, Richard N., "Principled
Design of the Modern Web Architecture", ACM Transactions on Internet Technology 2: 115–150,
doi:10.1145/514183.514185, ISSN 1533-5399 Fielding, Roy Thomas, Architectural Styles
and the Design of Network-based Software Architectures, Doctoral dissertation, University of California,
Irvine Pautasso, Cesare; Wilde, Erik; Alarcon, Rosa,
REST: Advanced Research Topics and Practical Applications
Pautasso, Cesare; Zimmermann, Olaf; Leymann, Frank, "RESTful Web Services vs. Big Web Services:
Making the Right Architectural Decision", 17th International World Wide Web Conference
Richardson, Leonard; Ruby, Sam, RESTful Web Services, O'Reilly, ISBN 978-0-596-52926-0
Ferreira, Otavio, Semantic Web Services: A RESTful Approach, IADIS, ISBN 978-972-8924-93-5
Notes