I strongly feel that RDF should be the foundation of Sutra, but it is not an easy fit. RDF's triplets of subject, predicate, and object do not fit well in a DB since the object may be a triplet or a container (bag, sequence, or alternative). I've been reading about RDF Schema, ontologies and OWL to learn how to restrict RDF's mutability to keep it compatible with a relational database. A well defined universe of creators (people), artifacts (files), locations, and events may keep RDF manageable so it can safely be mapped to and XML schema that itself can be mapped to a DB.
I think there are really three key tables, object, attribute, and link. Object but include some concept of type, creators, artifacts, locations and events being the foundation types. The attribute table only needs to handle strings; dates and numbers will be comparable if they are encoded right. The link table will be used to construct a graph of the objects.