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Note: The term "projection" is sometimes used as a synonym for the "federation" feature.

Limits of Federation

Federated content is accessible through the REST APi – however, some features will not work:

• Filesystem federation is currently read-only (though we plan to enable writable filesystem federation soon once a few outstanding issues are resolved).
• Access control can currently only be applied to an entire federated filesystem, not different access controls for different directories/files.
• Transactions are not available.
• Versioning is not available.
• Querying using the internal search functionality (including object counts and file size summaries) will not find federated content.

Filesystem Federation

Filesystem federation maps a node in the repository to a directory on disk.  This allows files on disk to be served and updated by Fedora 4 as though they were in the repository.  Filesystem federation avoids having to transfer files using HTTP – and with larger file sizes (or with larger numbers of files being processed), this can improve performance significantly.  If you are ingesting a large number of multi-gigabyte files, we recommend you consider filesystem federation.

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