The dramatic growth in the number of application domains that naturally generate probabilistic, uncertain data has resulted in a need for efficiently supporting complex querying and decision-making over such data. In this paper, we present a unified approach to ranking and top-k query processing in probabilistic databases by viewing it as a multi-criteria optimization problem, and by deriving a set of features that capture the key properties of a probabilistic dataset that dictate the ranked result. We contend that a single, specific ranking function may not suffice for probabilistic databases, and we instead propose two parameterized ranking functions, called PRF-w and PRF-e, that generalize or can approximate many of the previously proposed ranking functions. We present novel generating functions-based algorithms for efficiently ranking large datasets according to these ranking functions, even if the datasets exhibit complex correlations modeled using probabilistic and xor trees or Markov networks. We further propose that the parameters of the ranking function be learned from user preferences, and we develop an approach to learn those parameters. Finally, we present a comprehensive experimental study that illustrates the effectiveness of our parameterized ranking functions, especially PRF-e, at approximating other ranking functions and the scalability of our proposed algorithms for exact or approximate ranking.
@cite_15: Large databases with uncertain information are becoming more common in many applications including data integration, location tracking, and Web search. In these applications, ranking records with uncertain attributes needs to handle new problems that are fundamentally different from conventional ranking. Specifically, uncertainty in records' scores induces a partial order over records, as opposed to the total order that is assumed in the conventional ranking settings. In this paper, we present a new probabilistic model, based on partial orders, to encapsulate the space of possible rankings originating from score uncertainty. Under this model, we formulate several ranking query types with different semantics. We describe and analyze a set of efficient query evaluation algorithms. We show that our techniques can be used to solve the problem of rank aggregation in partial orders. In addition, we design novelsampling techniques to compute approximate query answers. Our experimental evaluation uses both real and synthetic data. The experimental study demonstrates the efficiency and effectiveness of our techniques in different settings.
@cite_50: Ranking is a fundamental operation in data analysis and decision support, and plays an even more crucial role if the dataset being explored exhibits uncertainty. This has led to much work in understanding how to rank uncertain datasets in recent years. In this paper, we address the problem of ranking when the tuple scores are uncertain, and the uncertainty is captured using continuous probability distributions (e.g. Gaussian distributions). We present a comprehensive solution to compute the values of a parameterized ranking function (PRF) [18] for arbitrary continuous probability distributions (and thus rank the uncertain dataset); PRF can be used to simulate or approximate many other ranking functions proposed in prior work. We develop exact polynomial time algorithms for some continuous probability distribution classes, and efficient approximation schemes with provable guarantees for arbitrary probability distributions. Our algorithms can also be used for exact or approximate evaluation of k-nearest neighbor queries over uncertain objects, whose positions are modeled using continuous probability distributions. Our experimental evaluation over several datasets illustrates the effectiveness of our approach at efficiently ranking uncertain datasets with continuous attribute uncertainty.
The aforementioned work has focused mainly on tuple uncertainty and discrete attribute uncertainty. Soliman and Ilyas @cite_15 were the first to consider the problem of handling continuous distributions. Recently, in a followup work @cite_50 , we extended the algorithm for to arbitrary continuous distributions. We were able to obtain exact polynomial time algorithms for some continuous probability distribution classes, and efficient approximation schemes with provable guarantees for arbitrary probability distributions. One important ingredient of those algorithms is an extension of the generating function used in this article.