For example, all the PCs in a company have serial numbers. When managers create policies, they have the physical resources in mind and may organize them hierarchically for various purposes. A department manager may label the PCs in his/her dept according to some hierarchical structure in the dept organization and assign policies accordingly. At the same time these PCs are company property and may be labeled independently by the IT dept in terms of who is responsible for maintenance on them.

If someone wants to take one of these PCs out of the building, maybe there is a policy that says even if the employee's manager says it is ok, the facilities manager must also approve before permission is granted. This can be modeled with a dept hierarchy and a facilities hierarchy, and there are rules within the hierarchy producing a result and policy combining between the 2 hierarchies that can resolve conflicts such as described above.

In the above example the /a1/b1/c1 might be the dept hierarchy and / a2/b2/c2 might be the facilities hierarchy.

It is also uniquely defined by a URI if a URI scheme has been applied to the same resources, since all the ancestors are readily identifiable within the URI.

Within the policies themselves, there would generally be no need to include this attribute except possibly for reporting purposes.