Revised Data Model

the data model has evolved slightly.

changes:
- added 'resource:parentid' to capture whether resource is original or
modified version
- added 'contributor:sponsorid' to track number of new contributors
registered by an existing contributor
- added 'log:contenttype' to capture whether content is object,
resource, subject or contributor
- reversed one-to-many direction of the contributor-subject relation
(original was a mistake)
- hilighted 'log' to denote it as entity rather than relation

explanations:
- possible 'action' data in log:
create,modify,copy,delete,view,login,logout

questions:
- should we allow unit content to be exposed in project view on a
per-unit basis? (this question previously noted)
- should we allow resource to be displayed inline in unit view on a
per-resource basis (where possible, given the type of resource, ie:
image, URL, etc)?
- should we allow a unit to be tied to a project as EITHER original
(only original creator can modify, therefore it might change/disappear)
OR copy (you gain control of further mods on it)?

notes:
- i'm thinking about collapsing 'resource' into 'object' and just
making it another type. if you have any thoughts about this, please
bring them up at our next meeting.

revised data model attached (please disregard previous version).