Hydra: Hypermedia-

Driven Web APIsMARIUS MÖSSMER

APRIL 30, 2014

Abstract

Hydra

is a lightweight vocabulary to create hypermedia-driven Web

APIs

it enables the creation of generic API clients

Authors

Markus Lanthaler, Graz University of Technology

Christian Gütl, Curtin University of Technology

Basic ideas of Hydra

With Hydra, a server is able to publish all possible state transitions a client

can perform on the server

Data is enriched with machine-readable semantics which enable interaction

Hydra APIs base upon

REST architectural style

HTTP

Building blocks of Hydra

Hydra consists of two fundamental parts:

JSON-LD

It’s the serialization format used in the communication between the server and its clients

Hydra Core Vocabulary

represents the shared vocabulary between server and client

JSON-LD

http://www.w3.org/TR/json-ld/

JSON-LD stands for Javascript Object Notation – Linked Data

JSON-LD is an extension of JSON

JSON-LD is a serialization-format

Use-cases:

Enables the expression of linked data

Makes data self-descriptive

JSON-LD

Simple JSON-document that represents a user-entity:

JSON-LD

Extended JSON-LD-document that represents a user-entity with meaningful

semantics:

Hydra Core Vocabulary

A small vocabulary extending RDF Schema ( http://www.w3.org/TR/rdf-

schema/ )

Hydra Core Vocabulary is used to

describe an application-domain with semantic aspects

express the behaviour of the Web-API

Hydra Core Vocabulary

Simple example: issue-tracking-system

GET http://example.com/issues/123

What‘s the model of comments

or how to add comments ?

Hydra Core

Vocabulary

GET http://example.com/api/vocab

Model of a comment-entity

Hydra Core

Vocabulary

GET http://example.com/api/vocab

Supported Operations

Hydra Core

Vocabulary

Full Overview

Hydra Project

Hydra W3C Community Group (http://www.w3.org/community/hydra/)

Mailing List

Wiki

Chat

Implementations

HydraBundle: a bundle for Symfony2 to create Web APIs based on Hydra

HydraConsole: a generic API console for Hydra-powered Web APIs

HydraClient: a PHP client library to access Hydra-powered Web APIs

Sources

http://www.hydra-cg.com/spec/latest/core/

http://www.w3.org/TR/json-ld/

http://www.w3.org/TR/rdf-schema/

http://www.markus-lanthaler.com/hydra/

M. Lanthaler and C. Gütl, “Hydra: A Vocabulary for Hypermedia-Driven

Web APIs”, 2013