Accord: Middleware Support for Contextual, Ubiquitous Data Management on User Devices

Abstract

People increasingly use a diverse array of computational devices, including desktop PCs, one or more laptops, a cell phone, a PDA, tablet PCs, digital music players, automobile computers, and so on. We present Accord, a middleware system we have implemented to manage user data across all of these devices. Accord emulates an ideal abstraction we call a user data-space: a virtual space in which user files exist independent of any particular physical device. Users put files into the space with whatever device is convenient, and later access those files using any of their devices. This abstraction is difficult to implement, and requires Accord to predict when a file will be needed and on which device. We describe two mechanisms the middleware uses to support such predictions: an object graph, which records contextual and statistical information about file objects, and a file transfer planner, which uses predictions to determine how to efficiently move files between devices despite connectivity, bandwidth and storage constraints. Predictions can be constructed using simple usage statistics, or from more complex machinelearned models of user activities. We also present experimental results demonstrating the effectiveness of our system.