What are Fedora Digital Objects?

The definition of a data object, as per the Fedora official documentation, is as follows:

A data object in a Fedora repository describes content (data and metadata) and a set of associated behaviors or services that can be applied to that content. Data objects comprise the bulk of a repository.

The figure below shows the basic data model of a Fedora Digital Object. The Fedora documentation describes the object model as a "compound digital object" design wherein multiple content items can be aggregated into a single digital object. Ofcourse, the contents themselves could be stored locally on the server running Fedora, or remotely (accessed using external URLs).

In addition, a data object in Fedora is defined using a customized XML schema language called Fedora Object XML (or FOXML for short).

As shown in the figure above, a Fedora digital object essentially comprises of 3 parts:

1. Digital Object Identifier: A unique, persistent identifier for the object.
2. System Properties: A set of system-defined descriptive properties that is necessary to manage and track the object in the repository.'
3. Datastream(s): The element in a Fedora digital object that represents a content item. These datastreams represent the digital content that is the essence of the digital object (e.g., digital images, encoded texts, audio recordings). All sorts of metadata, except system metadata, are also treated as content, and are therefore represented as datastreams in the object. Additionally, a datastream can reference any type of content, and that content can be stored either locally or remotely to the repository system.

In addition, the Fedora documentation makes the following observation about metadata associated with a digital object:

The FOXML metadata for a digital object is the metadata that must be recorded with every digital object to facilitate the management of that object. FOXML metadata is distinct from other metadata that is stored in the digital object as content. This type of metadata is the metadata that is required by the Fedora repository architecture. All other metadata (e.g., descriptive metadata, technical metadata) is considered optional from the repository standpoint, and is treated as a Datastream in a digital object.

(to be continued)