Using policy to control data synchronisation in middleware for an ad-hoc mobile network

Many devices are now using wireless communication, either by using base stations or by forming adhoc networks, but this style of mobile platform increases the probability of disconnection because of loss of network access. Replication of shared data is one way to increase data availability in a mobile environment, but leads to the problem of inconsistent copies of data after periods of disconnection, and so requires some means of data synchronisation. Therefore, there is a need for an approach that can provide synchronisation support for various types of wireless application. This thesis investigates how policy can be used to resolve problems of data conflict in a way that can be tailored to meet the needs of different types of application in different situations. A middleware has been created to investigate the problem. This middleware supports the sharing of data in a wireless environment using a tuple-space paradigm. It provides data caching which will enable individual devices sharing data to work with a single virtual space. This method does not guarantee that data in a local device will always be up-to-date but it does provide some level of information for applications that need the data for decision making while disconnected from other devices. A set of policies is maintained within the middleware, and these policies are used to express a wide range of synchronisation options to restore the consistency of the data after periods of disconnected operation. This thesis tests several policies in a number of scenarios based on different wireless applications. These involve a range of context information to support the policies in decision making. The thesis also includes an investigation into how policy can be defined independently for each device and the implementing of a synchronisation process that can support the process. Such environments require a more complex synchronisation process that can detect and resolve any policy conflict. The performance of the system has been measured and analysed in term of costs and benefits offered to applications. It shows that it is possible for such a system to have performance sufficient for applications that are not especially time sensitive in environments where the periods of connection are long enough for the system to progress its synchronisation.