A primary goal of context-aware systems is delivering the right information at the

right place and right time to users in order to enable them to make effective decisions and improve their quality of life. There are three key requirements for achieving this goal:

determining what information is relevant, personalizing it based on the users’ context (location, preferences, behavioral history etc.), and delivering it to them in a timely manner without an explicit request from them. These requirements create a paradigm that we term as “Proactive Context-aware Computing”.

Most of the existing context-aware systems fulfill only a subset of these requirements.

Many of these systems focus only on personalization of the requested information

based on users’ current context. Moreover, they are often designed for specific domains.

In addition, most of the existing systems are reactive - the users request for some information and the system delivers it to them. These systems are not proactive i.e. they cannot anticipate users’ intent and behavior and act proactively without an explicit request from them. In order to overcome these limitations, we need to conduct a deeper analysis and enhance our understanding of context-aware systems that are generic, universal, proactive and applicable to a wide variety of domains.

To support this dissertation, we explore several directions. Clearly the most significant

sources of information about users today are smartphones. A large amount of users’ context can be acquired through them and they can be used as an effective means

to deliver information to users. In addition, social media such as Facebook, Flickr and

Foursquare provide a rich and powerful platform to mine users’ interests, preferences and behavioral history. We employ the ubiquity of smartphones and the wealth of information available from social media to address the challenge of building proactive context-aware systems. We have implemented and evaluated a few approaches, including some as part of the Rover framework, to achieve the paradigm of Proactive Context-aware Computing. Rover is a context-aware research platform which has been evolving for the last 6 years.

Since location is one of the most important context for users, we have developed

‘Locus’, an indoor localization, tracking and navigation system for multi-story buildings.

Other important dimensions of users’ context include the activities that they are engaged

in. To this end, we have developed ‘SenseMe’, a system that leverages the smartphone and its multiple sensors in order to perform multidimensional context and activity recognition for users. As part of the ‘SenseMe’ project, we also conducted an exploratory study of privacy, trust, risks and other concerns of users with smart phone based personal sensing systems and applications.

To determine what information would be relevant to users’ situations, we have developed ‘TellMe’ - a system that employs a new, flexible and scalable approach based on Natural Language Processing techniques to perform bootstrapped discovery and ranking of relevant information in context-aware systems. In order to personalize the relevant information, we have also developed an algorithm and system for mining a broad range of users’ preferences from their social network profiles and activities. For recommending new information to the users based on their past behavior and context history (such as visited locations, activities and time), we have developed a recommender system and approach for performing multi-dimensional collaborative recommendations using tensor factorization.

For timely delivery of personalized and relevant information, it is essential to anticipate

and predict users’ behavior. To this end, we have developed a unified infrastructure,

within the Rover framework, and implemented several novel approaches and algorithms

that employ various contextual features and state of the art machine learning techniques

for building diverse behavioral models of users. Examples of generated models include

classifying users’ semantic places and mobility states, predicting their availability for accepting calls on smartphones and inferring their device charging behavior. Finally, to

enable proactivity in context-aware systems, we have also developed a planning framework based on HTN planning. Together, these works provide a major push in the direction of proactive context-aware computing.