Use case: Support Fedora 3-style object classes (content models)

We want to implement a Fedora repository using our own client. Since we are not using Islandora or Hydra frameworks to manage object classes, therefore the solution in Fedora 3 would be to set up content models that can be attached via "hasModel" relationships to objects.

If we decide to use F4 for our repository, we need a similar facility to rely on at repository level.

Specific F3-style use cases:

1. Attach a "published for web" content model to an object on the fly (through API or admin GUI). This CM is tied to a set of SDefs and SDeps that allow generation of, and access to, "web large" and "web small" derivatives. If the relationship is broken (also via API or admin GUI) those derivatives are not available any more.
2. Enforce datastream presence in an object. If we want to attach an "image resource" content model to an object, we want to make it mandatory for that object to have a MASTER datastream with mimetype image/tiff, image/png etc.
3. Enforce access policies and other relationships. Objects attached to "image resource" content model MAY NOT be attached to "text resource" or "multimedia resource" content models and MAY have a "isResourceOf" relationship with an object with "manufact" content model. DC properties of objects with "published for web" content model are readable by all.

These goals are determining for whether we may be able to implement F4.