Because no common model exists which is adequate for our PBX device we will have to create an extension schema. This will inherit from the core and common models but will be specific to our device. Before we launch into our schema, it is worth considering the ways in which we may modify and extend the core and common models. We could:
Add (or delete) a property to (from) an existing class or subclass
Add (or delete) classes
Turn an existing class into an Association
Add or delete qualifiers
Add (or delete) a method to (from) a class
Some of these activities will cause problems to other management systems. Deleting the CIM_OperatingSystem class, for example, or moving it other than downwards in its own hierarchy may not matter for your management system because it will know where to find it. If, however, your customer decides to manage your PBX with the same management system that he is using for your competitor's product, then it may not expect the class other than in CIM_EnabledLogicalElement's subtree .
We will therefore try to avoid deleting properties or classes from the core and common models.