Search

With the growing number of wireless and mobile devices ingrained into our daily lives, more and more people are interacting with online services that adopt recommender systems to suggest movies, news and points of interest. The private demographics of users such as age and gender in online recommender systems are very useful for many applications such as personalized ads, social study and marketing. However, users do not always provide details in their online profiles due to privacy concern. Most existing approaches can infer user private attributes based on sufficient interaction history but could fail for new users with few ratings. In this paper, we present a novel preference elicitation method, with which a recommender system asks cold-start users to rate selected items adaptively and infer the demographics rapidly via a few interactions. Specifically, latent user profiles are learned across the tasks of demographic inference and rating prediction simultaneously, which enables knowledge transfer through the two related tasks and improves the prediction accuracy for both tasks. The proposed method can also facilitate the understanding of the tradeoff between user privacy and the utility of personalization. Experimental results on real-world datasets demonstrate the performance of the proposed method in terms of the accuracy of both demographics inference and rating prediction.

The Domain Name System (DNS), which does not encrypt domain names such as "bank.us" and "dentalcare.com", commonly accurately reflects the specific network services. Therefore, DNS-based behavioral analysis is extremely attractive for many applications such as forensics investigation and online advertisement. Traditionally, a user can be trivially and uniquely identified by the device's IP address if it is static (i.e., a desktop or a laptop). As more and more wireless and mobile devices are deeply ingrained in our lives and the dynamic IP address such as DHCP has been widely applied, it becomes almost impossible to use one IP address to identify a unique user. In this paper, we propose a new tracking method to identify individual users by the way they query DNS regardless of dynamic changing IP addresses and various types of devices. The method is applicable based on two observations. First, even though users may update IP addresses dynamically during different sessions, their query patterns can be stable across these sessions. Secondly, domain name look ups in sessions are different from users to users according to their personal behaviors. Specifically, we propose the constrained Dirichlet multinomial mixture (CDMM) clustering model to cluster DNS queries of different sessions into groups, each of which is considered being generated by a unique user. Compared with traditional supervised and unsupervised models, our model does not acquire any labeled user information that is very hard to obtain in real networks or the specification of the number of clusters, and meanwhile enforces the maximum number of session data in each cluster, which fits the DNS tracking problem nicely. Experimental results on DNS queries collected from real networks demonstrate that our method accomplishes a high clustering accuracy and outperforms the existing methods.

In the competitive environment of the internet, retaining and growing one's user base is of major concern to most web services. Furthermore, the economic model of many web services is allowing free access to most content, and generating revenue through advertising. This unique model requires securing user time on a site rather than the purchase of good which makes it crucially important to create new kinds of metrics and solutions for growth and retention efforts for web services. In this work, we address this problem by proposing a new retention metric for web services by concentrating on the rate of user return. We further apply predictive analysis to the proposed retention metric on a service, as a means for characterizing lost customers. Finally, we set up a simple yet effective framework to evaluate a multitude of factors that contribute to user return. Specifically, we define the problem of return time prediction for free web services. Our solution is based on the Cox's proportional hazard model from survival analysis. The hazard based approach offers several benefits including the ability to work with censored data, to model the dynamics in user return rates, and to easily incorporate different types of covariates in the model. We compare the performance of our hazard based model in predicting the user return time and in categorizing users into buckets based on their predicted return time, against several baseline regression and classification methods and find the hazard based approach to be superior.

We introduce a new dissimilarity function for ranked lists, the expected weighted Hoeffding distance, that has several advantages over current dissimilarity measures for ranked search results. First, it is easily customized for users who pay varying degrees of attention to websites at different ranks. Second, unlike existing measures such as generalized Kendall's tau, it is based on a true metric, preserving meaningful embeddings when visualization techniques like multi-dimensional scaling are applied. Third, our measure can effectively handle partial or missing rank information while retaining a probabilistic interpretation. Finally, the measure can be made computationally tractable and we give a highly efficient algorithm for computing it. We then apply our new metric with multi-dimensional scaling to visualize and explore relationships between the result sets from different search engines, showing how the weighted Hoeffding distance can distinguish important differences in search engine behavior that are not apparent with other rank-distance metrics. Such visualizations are highly effective at summarizing and analyzing insights on which search engines to use, what search strategies users can employ, and how search results evolve over time. We demonstrate our techniques using a collection of popular search engines, a representative set of queries, and frequently used query manipulation methods.