HATEOAS

Last updated

Hypermedia as the engine of application state (HATEOAS) is a constraint of the REST software architectural style that distinguishes it from other network architectural styles. [1]

Contents

With HATEOAS, a client interacts with a network application whose application servers provide information dynamically through hypermedia. A REST client needs little to no prior knowledge about how to interact with an application or server beyond a generic understanding of hypermedia.

By contrast, clients and servers in Common Object Request Broker Architecture (CORBA) interact through a fixed interface shared through documentation or an interface description language (IDL).

The restrictions imposed by HATEOAS decouple client and server. This enables server functionality to evolve independently.

The term was coined in 2000 by Roy Fielding in his doctoral dissertation. [2]

Example

A user-agent makes an HTTP request to a REST API through an entry point URL. All subsequent requests the user-agent may make are discovered inside the response to each request. The media types used for these representations, and the link relations they may contain, are part of the API. The client transitions through application states by selecting from the links within a representation or by manipulating the representation in other ways afforded by its media type. In this way, RESTful interaction is driven by hypermedia, rather than out-of-band information. [3]

For example, this GET request fetches an account resource, requesting details in a JSON representation: [4] 

GET/accounts/12345HTTP/1.1Host:bank.example.com

The response is:

HTTP/1.1200OK  {     "account": {         "account_number": 12345,         "balance": {             "currency": "usd",             "value": 100.00         },         "links": {             "deposits": "/accounts/12345/deposits",             "withdrawals": "/accounts/12345/withdrawals",             "transfers": "/accounts/12345/transfers",             "close-requests": "/accounts/12345/close-requests"         }     } }

The response contains these possible follow-up links: POST a deposit, withdrawal, transfer, or close request (to close the account).

As an example, later, after the account has been overdrawn, there is a different set of available links, because the account is overdrawn.

HTTP/1.1200OK  {     "account": {         "account_number": 12345,         "balance": {             "currency": "usd",             "value": -25.00         },         "links": {             "deposits": "/accounts/12345/deposits"         }     } }

Now only one link is available: to deposit more money (by POSTing to deposits). In its current state, the other links are not available. Hence the term Engine of Application State. What actions are possible varies as the state of the resource varies.

A client does not need to understand every media type and communication mechanism offered by the server. The ability to understand new media types may be acquired at run-time through "code-on-demand" provided to the client by the server. [2]

Origins

The HATEOAS constraint is an essential part of the "uniform interface" feature of REST, as defined in Roy Fielding's doctoral dissertation. [2] Fielding has further described the concept on his blog. [3]

The purpose of some of the strictness of this and other REST constraints, Fielding explains, is "software design on the scale of decades: every detail is intended to promote software longevity and independent evolution. Many of the constraints are directly opposed to short-term efficiency. Unfortunately, people are fairly good at short-term design, and usually awful at long-term design". [3]

Implementations

See also

Related Research Articles

In distributed computing, a remote procedure call (RPC) is when a computer program causes a procedure (subroutine) to execute in a different address space, which is written as if it were a normal (local) procedure call, without the programmer explicitly writing the details for the remote interaction. That is, the programmer writes essentially the same code whether the subroutine is local to the executing program, or remote. This is a form of client–server interaction, typically implemented via a request–response message passing system. In the object-oriented programming paradigm, RPCs are represented by remote method invocation (RMI). The RPC model implies a level of location transparency, namely that calling procedures are largely the same whether they are local or remote, but usually, they are not identical, so local calls can be distinguished from remote calls. Remote calls are usually orders of magnitude slower and less reliable than local calls, so distinguishing them is important.

<span class="mw-page-title-main">Jakarta EE</span> Set of specifications extending Java SE

Jakarta EE, formerly Java Platform, Enterprise Edition and Java 2 Platform, Enterprise Edition (J2EE), is a set of specifications, extending Java SE with specifications for enterprise features such as distributed computing and web services. Jakarta EE applications are run on reference runtimes, which can be microservices or application servers, which handle transactions, security, scalability, concurrency and management of the components they are deploying.

A web service (WS) is either:

Hypermedia, an extension of hypertext, is a nonlinear medium of information that includes graphics, audio, video, plain text and hyperlinks. This designation contrasts with the broader term multimedia, which may include non-interactive linear presentations as well as hypermedia. The term was first used in a 1965 article written by Ted Nelson. Hypermedia is a type of multimedia that features interactive elements, such as hypertext, buttons, or interactive images and videos, allowing users to navigate and engage with content in a non-linear manner.

REST is a software architectural style that was created to guide the design and development of the architecture for the World Wide Web. REST defines a set of constraints for how the architecture of a distributed, Internet-scale hypermedia system, such as the Web, should behave. The REST architectural style emphasises uniform interfaces, independent deployment of components, the scalability of interactions between them, and creating a layered architecture to promote caching to reduce user-perceived latency, enforce security, and encapsulate legacy systems.

In computing, Web-Based Enterprise Management (WBEM) comprises a set of systems-management technologies developed to unify the management of distributed computing environments. The WBEM initiative, initially sponsored in 1996 by BMC Software, Cisco Systems, Compaq Computer, Intel, and Microsoft, is now widely adopted. WBEM is based on Internet standards and Distributed Management Task Force (DMTF) open standards:

<span class="mw-page-title-main">Dynamic web page</span> Type of web page

A dynamic web page is a web page constructed at runtime, as opposed to a static web page, delivered as it is stored.

<span class="mw-page-title-main">Roy Fielding</span> American computer scientist

Roy Thomas Fielding is an American computer scientist, one of the principal authors of the HTTP specification and the originator of the Representational State Transfer (REST) architectural style. He is an authority on computer network architecture and co-founded the Apache HTTP Server project.

<span class="mw-page-title-main">Web API</span> HTTP-based application programming interface on the web

A web API is an application programming interface (API) for either a web server or a web browser. As a web development concept, it can be related to a web application's client side. A server-side web API consists of one or more publicly exposed endpoints to a defined request–response message system, typically expressed in JSON or XML by means of an HTTP-based web server. A server API (SAPI) is not considered a server-side web API, unless it is publicly accessible by a remote web application.

Web-oriented architecture (WOA) was coined in 2006 by Nick Gall of Gartner. It is a software architecture style that extends service-oriented architecture (SOA) to web-based applications. WOA was originally created by many web applications and sites, such as social websites and personal websites.

Jakarta RESTful Web Services, is a Jakarta EE API specification that provides support in creating web services according to the Representational State Transfer (REST) architectural pattern. JAX-RS uses annotations, introduced in Java SE 5, to simplify the development and deployment of web service clients and endpoints.

In computing, Open Data Protocol (OData) is an open protocol that allows the creation and consumption of queryable and interoperable Web service APIs in a standard way. Microsoft initiated OData in 2007. Versions 1.0, 2.0, and 3.0 are released under the Microsoft Open Specification Promise. Version 4.0 was standardized at OASIS, with a release in March 2014. In April 2015 OASIS submitted OData v4 and OData JSON Format v4 to ISO/IEC JTC 1 for approval as an international standard. In December 2016, ISO/IEC published OData 4.0 Core as ISO/IEC 20802-1:2016 and the OData JSON Format as ISO/IEC 20802-2:2016.

An application programming interface (API) is a connection between computers or between computer programs. It is a type of software interface, offering a service to other pieces of software. A document or standard that describes how to build such a connection or interface is called an API specification. A computer system that meets this standard is said to implement or expose an API. The term API may refer either to the specification or to the implementation.

JSON-WSP is a web service protocol that uses JSON for service description, requests and responses. It is inspired from JSON-RPC, but the lack of a service description specification with documentation in JSON-RPC sparked the design of JSON-WSP.

Cloud Infrastructure Management Interface (CIMI) is an open standard API specification for managing cloud infrastructure.

RESTful API Modeling Language (RAML) is a YAML-based language for describing static APIs. It provides all the information necessary to describe APIs on the level 2 of the Richardson Maturity Model. Although designed with RESTful APIs in mind, RAML is not capable of describing APIs that obey all constraints of REST. It encourages reuse, enables discovery and pattern-sharing and aims for merit-based emergence of best practices.

Hypertext Application Language (HAL) is a convention for defining hypermedia such as links to external resources within JSON or XML code. It is documented in an Internet Draft, with the latest version 11 published the 10th of October 2023. The standard was initially proposed in June 2012, specifically for use with JSON, and has since become available in two variations, JSON and XML. The two associated MIME types are application/hal+xml and application/hal+json.

RESTfulAPIDLs are formal languages designed to provide a structured description of a RESTful web API that is useful both to a human and for automated machine processing. API description languages are sometimes called interface description languages (IDLs). The structured description might be used to generate documentation for human programmers; such documentation may be easier to read than free-form documentation, since all documentation generated by the same tool follows the same formatting conventions. Additionally, the description language is usually precise enough to allow automated generation of various software artifacts, like libraries, to access the API from various programming languages, which takes the burden of manually creating them off the programmers.

The Richardson Maturity Model (RMM) is a maturity model suggested in 2008 by Leonard Richardson which classifies Web APIs based on their adherence and conformity to each of the model's four levels. The aim of the research of the model as stated by the author was to find out the relationship between the constraints of REST and other forms of web services.

htmx is an open-source front-end JavaScript library that extends HTML with custom attributes that enable the use of AJAX directly in HTML and with a hypermedia-driven approach. These attributes allow for the dynamic definition of a web page directly in HTML and CSS, without the need for writing additional JavaScript. These attributes allows tasks that traditionally required writing JavaScript to be done completely with HTML. The library was created by Carson Gross as a new version of intercooler.js.

References

  1. ↑ M. Kelly (21 April 2024). "Internet Draft : JSON Hypertext Application Language". datatracker.ietf.org.
  2. 1 2 3 Fielding, Roy Thomas (2000). "Rizwan.Ali 03014821766 State Transfer (REST)". Architectural Styles and the Design of Network-based Software Architectures (PhD). University of California, Irvine. p. 82. ISBN   0599871180.
  3. 1 2 3 4 Fielding, Roy T. (20 Oct 2008). "REST APIs must be hypertext-driven" . Retrieved 20 May 2010.
  4. ↑ Thijssen, Joshua (2016-10-29). "What is HATEOAS and why is it important for my REST API?". REST CookBook. Retrieved 2020-02-05.
  5. ↑ Gross, Carson. "HATEOAS". htmx.org. This, despite the fact that neither XML nor JSON was a natural hypermedia in the same manner as HTML.
  6. ↑ Siren: a hypermedia specification for representing entities on GitHub
  7. ↑ "Collection+JSON - Hypermedia Type" . Retrieved 2021-10-25.
  8. ↑ "JSON API: Latest Specification" . Retrieved 2021-10-25.
  9. ↑ "Hydra: Hypermedia-Driven Web APIs" . Retrieved 2021-10-27.
This page is based on this Wikipedia article
Text is available under the CC BY-SA 4.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.