Security on sergments (Framework Manager model)

[cognosgem]

We have created a master model with a Physical Layer and Imported Metadata data(Query Subjects) in it. The physical layer is segmented, so that, any other projects can link their models to Physical layer and inherit Query subjects from Physical layer of master model. Whenever a query subject is added or deleted in master model physical layer, the changes are also reflected in other models that are linked to master model (it is pretty obviuos functionality). The problem is whenever an object is added or deleted in other models, that is also impacting physical layer of master model i.e.the objects are also added or deleted physical layer of master model. We want to enforce some security on Physical layer of master model and centralized control, so that, any modifications to Physical layer in master model should reflect in other models and not vice versa i.e. any additions or deletion by other model developers should not impact master model physical layer.

We have given the following a try, but do not cater to our needs :

1. Including master model in version control software like visual source safe, so that, we can keep track of any changes to master model physical layerÃ,  by other model developers.Ã,  This is not serving actual purpose, since the developers of other models still can delete or add objects to Physical layer in master model.

2. File based security. Giving read only permission on master model.xml should prevent others to modify, but we are not successful in this also.

Any expert advice on this?