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Hydra Community Group

Building Web APIs seems still more an art than a science. How can we build APIs such that generic clients can easily use them? And how do we build those clients? Current APIs heavily rely on out-of-band information such as human-readable documentation and API-specific SDKs. However, this only allows for very simple and brittle clients that are hardcoded against specific APIs. Hydra, in contrast, is a set of technologies that allow to design APIs in a different manner, in a way that enables smarter clients. The foundation is laid by the Hydra Core Vocabulary. It defines a number of fundamental concepts, such as hypermedia controls and collections, which allow machines to understand how to interact with an API. Since all information about the API is available in a machine-readable form, completely generic clients become possible. The Core Vocabulary is complemented by Linked Data Fragments, a set of specifications that enable advanced yet efficient client-side querying of Web APIs. More information about these technologies can be found on our homepage:


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Hydra Core Vocabulary

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Hydra welcomes Linked Data Fragments

Hydra enables us to build better APIs, and in particular, APIs that are accessible by generic clients. One part of this is to capture the fundamental building blocks of APIs, such as hypermedia controls and collections. This is what the Hydra Core Vocabulary does. So far, the effort of the Hydra Community Group has focused on the development of this vocabulary, and with great success: the many discussions on the Hydra mailing list show the interest and engagement of a lot of people.

Today, the Hydra project welcomes a second part: Linked Data Fragments, a set of technologies for advanced and efficient client-side querying of APIs. The Linked Data Fragments specification describes a uniform vision on all kinds of APIs that offer Linked Data representations, like JSON-LD or Turtle. By defining specific kinds of fragments, such as Triple Pattern Fragments, clients can efficiently execute complex queries. The Hydra Core Vocabulary is an enabler for these technologies.

What do Linked Data Fragments look like?
See a Linked Data Fragments API in action on, and try a Linked Data Fragments client at The complete source code is available on GitHub.

What does this mean for the Hydra project?
As of today, Hydra will be the home of three specifications:

How to discuss and participate?
If you haven’t done so yet, join the Hydra Community Group (you need a free W3C account). If you have questions, send a mail to our mailing list.

We look forward to your feedback!

Hydra Community Group Launched

I’m happy to announce the launch of the Hydra Community Group and would like to thank everyone who made it possible.

The goal of this group is to simplify developer’s lives by creating a set of technologies and tools supporting the creation of truly RESTful Web APIs and generic clients. As the name of the group already suggests, Hydra will be taken as the starting point towards this ambitious goal. However, the group may decide to change or extend Hydra in various ways or move into a different direction altogether. I’m pretty excited about the role the Hydra Community Group will play in solving this challenging problem.

This is an open group which means that you can join at any time by a simple click—all you need is a W3C account. If you are not sure yet whether to join the group, you may find the archives of our mailing list of interest.