It is well recognized that context plays a significant role in all human endeavors. All decisions are based on information which has to be interpreted in context. By making information systems context-aware we can have systems that significantly enhance human capabilities to make critical decisions.

A major challenge of context-aware systems is to balance usability with generality and extensibility. The relevant context changes depending on the particular application. The model used to represent the context and its relationship to entities must be general

enough to allow additions of context categories without redesign while remaining usable across many applications. Also, while efforts are put in by application designers and developers to make applications context-aware, these efforts are customized to specific

needs of the target application, and only certain common contexts like location and time are taken into account. Therefore, a general framework is called for that can (i) efficiently maintain, represent and integrate contextual information, (ii) act as an integration platform

where different applications can share contexts and (iii) provide relevant services to make efficient use of the contextual information. This dissertation presents:

• a generic and effective context model - Rover Context Model (RoCoM) that is structured around four primitives: entities, events, relationships, and activities; and practically usable through the concept of templates,

• a flexible, extensible and generic ontology - Rover Context Model Ontology (RoCoMO) supporting the model, that addresses the shortcomings of existing ontologies,

• an effective mechanism of modeling the context of a situation, through the concept of relevant context, with the help of situation graph, efficiently handling and making best use of context information,

• a context middleware - Rover-II, which serves as a framework for contextual information integration, that could be used not just to store and compile the contextual information, but also integrate relevant services to enhance the context information; and more importantly, enable sharing of context among the applications subscribed

to it,

• the initial design and implementation of a distributed architecture for Rover-II, following a P2P arrangement inspired from Tapestry,

The above concepts are illustrated through M-Urgency, a context-aware public safety system that has been deployed at the University of Maryland Police Department.