This paper describes an extended role-based access control (RBAC) model, which makes RBAC sensitive to the
context
of an attempted operation. Traditional RBAC does not specify whether the permissions associated with a role enable access to a
particular
object, or to some
subset
of objects belonging to a class. We extend the model by introducing the notions of role context and context filters. Context filters are Boolean expressions based on the context of the user attempting the operation, as well as the context of the object upon which the operation is attempted. By supplying context filters during the definition of a role, a security administrator can easily limit the applicability of users' role memberships to particular subsets of the target objects. We also describe our implementation of the model in a web-services platform, to illustrate how this technique is particularly valuable when the data is hierarchically structured.
The problem of tooth discoloration is emerging in our society because of the poor oral hygiene, physical agents, environmental chemicals, mouth rinses, some dental procedures, general systemic conditions, and drugs. Other common causes of tooth discoloration include excessive use of tea, coffee, tobacco smoking and chewing, chewing of betel morsel (piper betel, paan), and so on. Drug-induced tooth discoloration can be prevented by avoiding prescriptions of well-known offender drugs known to cause tooth discoloration during pregnancy and in young children. This review describes some important groups of drugs that cause tooth discoloration.
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