The model has been implemented in SQL Server 2000/2005, but requires no special features of that product.

Essentially, the model presents to the user a set of records from a single table that's generated by the union of a set of filters, and which is maintained by triggers. So changes to the underlying data (which affects each filter's output), or even changing the set of filters, is automatically witnessed by each user in a way that depends on what filters they've been assigned by way of their roles.

A similar thing could be written for intersections, so the model's core idea may be useful elsewhere.