Note to Users

In distributed and mobile environments, the connections among the hosts on which a software system is running are often unstable. As a result of connectivity losses, the overall availability of the system decreases. The distribution of software components onto hardware nodes (i.e., deployment architecture) may be ill-suited for the given target hardware environment and may need to be altered to improve the software system's availability. The critical difficulty in achieving this task lies in the fact that determining a software system's deployment that will maximize its availability is an exponentially complex problem. In this dissertation, we motivate, present, and evaluate an automated, flexible, software architecture-based solution for disconnected operation that increases the availability of the system during disconnection. We provide a set of models, algorithms, techniques, and tools for improving a distributed, mobile system's availability via redeployment, by enabling the system to (1) monitor its operation; (2) estimate its deployment architecture; and (3) effect that architecture automatically. While the focus of this dissertation research is on improving system availability, our methodology is extensible to support other non-functional properties that may be relevant in a given distributed system.