Jeff Silvis's Blog

RepoMMan, REMAP and Hydra at Hull

Towards a Repository-enabled Scholar's Workbench
D-Lib Magazine
May/June 2009
Volume 15 Number 5/6
Richard Green Chris Awre

Technology in more detail

Hydra sets

Hydra content models and disseminators <-- Only hit in google for " "Hydra sets" fedora'
Hydra sets There are two basic models for managing "Sets", our preferred name over "collections" or "folders". * Explicit set relationships in which the set object contains an explicit listing of its set members * Implicit set relationships in which the set object has no explicit listing but rather contains some rule(s) for identifying its set members In all cases there must be a single object that represents the set itself in the repository, an object that defines and describes the set (in the abstract and/or for specific UI use) and provides a reference point (a PID) for creating object associations to the set. The various models described below concern the manner in which member objects are identified and managed. There are many relationships that could be used to define a set (explicit or implicit) in RDF. Hydra will always use 'hasMember' or its converse 'isMemberOf' as appropriate (cf 'hasPart' and 'isPartOf' for aggregate objects); this does not preclude users working with other relationships. Hydra will reserve 'isMemberOfCollection' for use in the specific case of OAI-PMH harvesting sets. Expicit sets Parent object may designate members via "hasMember {childPID}" triples in RELS-EXT, or Parent object may designate members via a METS structmap or similar mechanism Explicit sets represent a useful approach when there is a one-time determination of a closed set. Implicit sets The set object for an implicit set has no itemised 'knowledge' of its set members but contains the information needed to retrieve them. This may take the form of a query against the repository Resource Index (where the members each contain an 'isMemberOf' assertion in RELS-EXT) or a more general query or search across the repository (find all photographs where the subject is Barack Obama), or some other rules-based selection. An extra datastream will be required in the set object to contain the query or rules necessary to retrieve the set membership information.