Overview
Within Fedora 4, snapshots of the current state of an object may be saved into the version history either through explicit user requests or during each update to that object. The properties or content of a node saved in these version checkpoints may be accessed later to serve as a historical record of the object. Future feature development may allow for easy reversion to prior versions, export of the entire history or other useful actions.Creating versions
Explicit version creation
When you wish to save a snapshot of the current version of a node to the version history you can use the REST API. When saving these versions you can optionally provide a label that both serves to easily differentiate a version from another and allows easy retrieval of that version.
Duplicate Version Labels
Version creation is a relatively costly operation. With the ability to create versions whenever you wish, you can develop workflows that maximize the utility of the version history.
Possible strategies include:
- For batch operations, only create version checkpoints once nodes have been ingested, verified and tested.
- For high value but small data such as descriptive metadata entered by subject experts, set a versioning policy to store every modification to capture the entirety of the curatorial endeavor.
- Create snapshot versions that correspond to released versions of content (ie, version X of a shared dataset, controlled vocabulary or collection)
Implicit version creation
If you wish to save a full history of a node by having versions created every time the node is updated, you can set the property "fedoraconfig:versioningPolicy" to "auto-version". This can be achieved using the sparql update form on the HTML view of the object or by using some other HTTP client software to invoke REST endpoints.
PREFIX fedoraconfig: <http://fedora.info/definitions/v4/rest-api#>
INSERT DATA { <> fedora:versioningPolicy "auto-version" }
If your needs for digital preservation are highest and you're willing to sacrifice a little bit of performance, you can set up repository-wide automatic versioning.
Viewing old Versions
From the HTML view (or by issuing HTTP GET methods in an HTTP client program) you can get the version history of a node by appending "/fcr:versions" to it's base URL. The root version will always be listed and represents the object at inception. Following the root version will be any other versions created. When labels have been specified, those labels will be displayed, otherwise the version will be identified by the modification date.
Previewing historic properties
By clicking on the box for a version you can expand and collapse a view of the version properties.
Navigating to the full view of an historic version
By clicking on the label of a version in the version listing you will be taken to the stored version of that resource. Because it's part of the historic record, you cannot edit it and certain properties have been stored in different property names (mixin types, uuid) but you can export that snapshot or view any content.
Feature Note
Future versions of fedora will allow reversion to previous versions.
Turn off Node Versioning
The fedora repository can operate with unversionable nodes as well as versionable nodes. By default, the "mix:versionable" mixin is applied to newly created fedora nodes. This enables versioning (though does not necessarily result in the creation of versions) for that node. Version-related operations will not work against unversionable nodes, an the presence of the "versioning-policy" will have no effect.
See how to make fedora nodes unversionable here.
