Role-based access control (RBAC) models have generated a great interest in the security community as a powerful and generalized approach to security management. In many practical scenarios, users may be restricted to assume roles only at predefined time periods. Furthermore, roles may only be invoked on prespecified intervals of time depending upon when certain actions are permitted. To capture such dynamic aspects of a role, a temporal RBAC (TRBAC) model has been recently proposed. However, the TRBAC model addresses the role enabling constraints only. In this paper, we propose a Generalized Temporal RoleBased Access Control (GTRBAC) model capable of expressing a wider range of temporal constraints. In particular, the model allows expressing periodic as well as duration constraints on roles, user-role assignments, and role-permission assignments. In an interval, activation of a role can further be restricted as a result of numerous activation constraints including cardinality constraints and maximum active duration constraints. The GTRBAC model extends the syntactic structure of the TRBAC model and its event and trigger expressions subsume those of TRBAC. Furthermore, GTRBAC allows expressing role hierarchies and separation of duty (SoD) constraints for specifying fine-grained temporal semantics.

Multimedia computer systems are required to store, retrieve, and communicate objects comprised of mixed data types including images, text and voice. An important aspect of multimedia systems is the integration of elements retrieved from databases distributed across a network. Integration of object components requires consideration of the temporal characteristics of multimedia elements. We propose a technique for the formal specification and modeling of multimedia composition with respect to intermedia timing. The proposed model is based on the logic of temporal intervals, and Timed Petri Nets. A strategy is evinced for constructing a database schema to facilitate data storage and retrieval of media elements based on the temporal relationships established by the proposed modeling tool. We present an algorithm which allows the retrieval of media elements from the constructed database in a manner which preserves the temporal requirements of the initial specification. Through the proposed model, the synchronization requirements of complex structures of temporally related objects can be easily specified.

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Abstract-Multimedia data often have time dependencies that must be satisfied at presentation time. To support a general-purpose multimedia information system, these timing relationships must be managed to provide utility to both the data presentation system and the multimedia author.In this paper we propose new conceptual models for capturing these timing relationships and managing them as part of a database. Specifically, we introduce and define n-ary and reverse temporal relations along with their temporal constraints. These new relations are a generalization of our earlier temporal models and establish the basis for conceptual database structures and temporal access control algorithms to facilitate forward, reverse, and partial-interval evaluation during multimedia object playout. The proposed relations are defined to ensure a property of monotonically increasing playout deadlines to facilitate both real-time deadline-driven playout scheduling or optimistic interval-based process playout.Furthermore, we show a translation of the conceptual models to a structure suitable for a relational database.