Collections

Those trained by the academic tradition of the western world like to think in terms of categories and collections. Categories in Fedora are modelled by the Content Models, but there is no system in place for Collections. But Fedora allows for RDF relations between objects, and with that we can easily model collections.

There is no inherent semantic meaning attached to collections. They are a way to group objects, pertaining to some criteria.

Content Models are also part of collections, preferably the collections containing objects that use them. Template objects are also part of collections.

A special collection doms:DOMS_Base_Collection contains the base objects of the DOMS system, described in DataModel. This collection will always be present.

The Collection Hierarchy

In the doms-relations namespace (see DomsNameSpacesAndSchemas) we define a reserved relation "isPartOfCollection". All objects must have at least one such relation to a Collection object (ie. an object of doms:ContentModel_Collection). This includes the collection objects themselves, and as such there is a hierarchy of collections.

At the top, we have defined a special collection object, called doms:Root_Collection. This collection contains itself. Collections can contain other collections, but cycles in the graph is explictly forbidden. The only accepted cycle is the root collection that contain itself.

Aside from forbidding cycles, there are no requirements for the structure of the graph. We envisage two ways to use collections

1. As a strict hierarchy, modelled on the organisational structure and the areas of responsibility. Few collections, and objects are not part of many collections.
2. As a way of adding tags (subjects) to the objects. There will be many collection objects, and objects will be part of many collections.