Hypermedia on the Web: A Definition

The value of "Connection-First" designs

Below is an excerpt from my book "RESTful Web API Patterns and Practices Cookbook" from O'Reilly Media

Ted Nelson is credited with coining the terms hypertext and hypermedia as early as the 1950s. He used these terms in his 1965 ACM paper “Complex Information Processing: A File Structure for the Complex, the Changing and the Indeterminate”. In its initial design, according to Tomas Isakowitz (in 2008), a hypertext system “consists of nodes that contain information, and of links, that represent relationships between the nodes.” Hypermedia systems focus on the connections between elements of a system.

Essentially, hypermedia provides the ability to link separate nodes, also called resources, such as documents, images, services, even snippets of text within a document, to each other. On the network, this connection is made using universal resource identifiers (URIs). When the connection includes the option of passing some data along, these links are expressed as forms that can prompt human users or scripted machines to supply inputs, too. HTML, for example, supports links and forms through tags such as <A>, <IMG>, <FORM>, and others. There are several formats that support hypermedia links and forms.

These hypermedia elements can also be returned as part of the request results. The ability to provide links and forms in responses gives client applications the option of selecting and activating those hypermedia elements in order to progress the application along a path. This makes it possible to create a network-based solution that is composed entirely of a series of links and forms (along with returned data) that, when followed, provide a solution to the designed problem (e.g., compute results; retrieve, update, and store data at a remote location; etc.).

The most common Web-based solutions focus on the resources (RESTful), the data (GraphQL), or the events (Asynchronous APIs). Hypermedia-based designs focus, instead, on the connections themselves. 

Links and forms provide a generality of interfaces (use of hypermedia documents over HTTP, for example) that powers hypermedia-based applications. Hypermedia-based client applications, like the HTML browser, and a command-line application like HyperCLI, can take advantage of this generality to support a wide range of new applications without ever having their source code modified or updated. We simply browse from one solution to the next by following (or manually typing) links, and use the same installed client application to read the news, update our to-do list, play an online game, etc.

Web-based applications can take advantage of hypermedia-based designs in order to power not just human-driven client applications like HTML browsers, but also machine-drive applications. This is especially helpful for clients that rely on APIs to access services on the network; even services that can be enlisted in a complete solution even though they know nothing about each other. That's the real value of hypermedia designs and implementations.