Hydra is based on four major components:
- the Fedora Commons software providing a robust, durable repository layer for persisting and managing digital objects.
- Solr indexes, providing fast access to information about the institution’s resources. Solr can be used as a lingua franca: content from any source that can generate a Solr index (perhaps an OPAC, or repository metadata records with different schema) can potentially be brought into a Hydra discovery environment.
- Blacklight, a Ruby on Rails plugin that sits above Solr and provides faceted searching, browsing and tailored views on objects
- HydraHead, a Ruby on Rails gem that works with ActiveFedora, another gem, to provide create, update and delete actions against objects in the repository, as well as to support various content management actions (e.g., upload file, edit metadata, change permissions).
There are a number of other gems that Hydra has written and that are maintained by the community. With all these building blocks it is possible to create a wide range of repository solutions. Indeed, it is not necessary to implement full Hydra solutions: a number of institutions have made use of some of our software components and/or design principles in conjunction with other systems.
The Hydra technical framework and its parts are more fully explained on the Hydra wiki.