Object Creation Service
When one or more new bytestreams (generally the contents of files and also known as blobs) are added to DuraCloud storage, the Object Creation Service (OCS) creates a Fedora Digital Object (FDO) that acts as a logical container for them. FDOs are able to record information identifying one or more closely related bytestreams and additional information about them. It does this by creating small XML document, for this project, using the FOXML schema. In this way, the FDO (as FOXML) can represent related information in a way that a bytestream store cannot easily do. This is a very flexible approach because it exploits a convenient, well supported separation of concerns found between bytestreams and organizations of related bytestreams.
The Object Creation Service may use any information to make a FDO (as FOXML) for the newly added bytestreams. This includes information obtained by introspecting on the bytestreams, DuraCloud functionality, DfR-related functionality or outside information. Simple FDOs can be created at first and later extended as more information is made available, possibly through applications acting a front-end to DfR functionality such as Islandora.
For this implementation, the FDOs created by the OCS will be ingested into a Fedora Repository hosted as part of the DfR. A Fedora Repository is a kind of flexible middleware that supports the use of many front-end applications, permits the integration of additional services and acts as a mediator for storage. For DfR, the storage will be provided by DuraCloud. It is also an integrated family of services that permits ingest, discovery, access and other functionality over a body of content both "conceptually" stored within it or references by it. Since the bytestreams will already be stored in DuraCloud when the OCS is called, it needs only to create the FDO, referencing the existing bytestreams by their DuraCloud identifiers, and ingest the newly created FDO. This means the FDO (actually an XML bytestream) is stored back into DuraCloud. Indeed all the content is stored in DuraCloud. DfR's approach to storage permits a number of benefits that will be explained in a separate section.
The Fedora Repository Service (and related services) provides ways to access the content (stored in DuraCloud) including information the content that is beyond the native capabilities of DuraCloud. In particular, you can discover relationships between content items and access them within the context of understanding the relationships. You can still access DuraCloud content directly but access through Fedora provides a richer experience. The Object Creation Service is the starting place for enriching DfR content deposited directly via DuraCloud by creating the FDOs to contain the information needed to provide an enriched experience.
