Results 1  10
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83
Provenance semirings
 PODS'07
, 2007
"... We show that relational algebra calculations for incomplete databases, probabilistic databases, bag semantics and whyprovenance are particular cases of the same general algorithms involving semirings. This further suggests a comprehensive provenance representation that uses semirings of polynomials. ..."
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Cited by 196 (29 self)
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We show that relational algebra calculations for incomplete databases, probabilistic databases, bag semantics and whyprovenance are particular cases of the same general algorithms involving semirings. This further suggests a comprehensive provenance representation that uses semirings of polynomials. We extend these considerations to datalog and semirings of formal power series. We give algorithms for datalog provenance calculation as well as datalog evaluation for incomplete and probabilistic databases. Finally, we show that for some semirings containment of conjunctive queries is the same as for standard set semantics.
Efficient topk query evaluation on probabilistic data
 in ICDE
, 2007
"... Modern enterprise applications are forced to deal with unreliable, inconsistent and imprecise information. Probabilistic databases can model such data naturally, but SQL query evaluation on probabilistic databases is difficult: previous approaches have either restricted the SQL queries, or computed ..."
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Cited by 182 (32 self)
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Modern enterprise applications are forced to deal with unreliable, inconsistent and imprecise information. Probabilistic databases can model such data naturally, but SQL query evaluation on probabilistic databases is difficult: previous approaches have either restricted the SQL queries, or computed approximate probabilities, or did not scale, and it was shown recently that precise query evaluation is theoretically hard. In this paper we describe a novel approach, which computes and ranks efficiently the topk answers to a SQL query on a probabilistic database. The restriction to topk answers is natural, since imprecisions in the data often lead to a large number of answers of low quality, and users are interested only in the answers with the highest probabilities. The idea in our algorithm is to run in parallel several MonteCarlo simulations, one for each candidate answer, and approximate each probability only to the extent needed to compute correctly the topk answers. The algorithms is in a certain sense provably optimal and scales to large databases: we have measured running times of 5 to 50 seconds for complex SQL queries over a large database (10M tuples of which 6M probabilistic). Additional contributions of the paper include several optimization techniques, and a simple data model for probabilistic data that achieves completeness by using SQL views. 1
A Unified Approach to Ranking in Probabilistic Databases
"... 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 decisionmaking over such data. In this paper, we present a unified approach to ranking and topk query processing in ..."
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Cited by 62 (3 self)
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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 decisionmaking over such data. In this paper, we present a unified approach to ranking and topk query processing in probabilistic databases by viewing it as a multicriteria 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 P RF ω and P RF e, that generalize or can approximate many of the previously proposed ranking functions. We present novel generating functionsbased 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 P RF e, at approximating other ranking functions and the scalability of our proposed algorithms for exact or approximate ranking. 1.
On the expressiveness of probabilistic XML models
, 2009
"... Various known models of probabilistic XML can be represented as instantiations of the abstract notion of pdocuments. In addition to ordinary nodes, pdocuments have distributional nodes that specify the possible worlds and their probabilistic distribution. Particular families of pdocuments are de ..."
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Cited by 47 (24 self)
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Various known models of probabilistic XML can be represented as instantiations of the abstract notion of pdocuments. In addition to ordinary nodes, pdocuments have distributional nodes that specify the possible worlds and their probabilistic distribution. Particular families of pdocuments are determined by the types of distributional nodes that can be used as well as by the structural constraints on the placement of those nodes in a pdocument. Some of the resulting families provide natural extensions and combinations of previously studied probabilistic XML models. The focus of the paper is on the expressive power of families of pdocuments. In particular, two main issues are studied.
and J.Huang. “Using OBDDs for Efficient Query Evaluation on Probabilistic Databases
 In Proc. SUM
, 2008
"... Abstract. We consider the problem of query evaluation for tuple independent probabilistic databases and Boolean conjunctive queries with inequalities but without selfjoins. We approach this problem as a construction problem for ordered binary decision diagrams (OBDDs): Given a query q and a probabi ..."
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Cited by 41 (15 self)
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Abstract. We consider the problem of query evaluation for tuple independent probabilistic databases and Boolean conjunctive queries with inequalities but without selfjoins. We approach this problem as a construction problem for ordered binary decision diagrams (OBDDs): Given a query q and a probabilistic database D, we construct in polynomial time an OBDD such that the probability of q(D) can be computed linearly in the size of that OBDD. This approach is applicable to a large class of queries, including the hierarchical queries, i.e., the Boolean conjunctive queries without selfjoins that admit PTIME evaluation on any tupleindependent probabilistic database, hierarchical queries extended with inequalities, and nonhierarchical queries on restricted databases. 1
Probabilistic data exchange
 In Proc. ICDT
, 2010
"... The work reported here lays the foundations of data exchange in the presence of probabilistic data. This requires rethinking the very basic concepts of traditional data exchange, such as solution, universal solution, and the certain answers of target queries. We develop a framework for data exchange ..."
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Cited by 40 (7 self)
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The work reported here lays the foundations of data exchange in the presence of probabilistic data. This requires rethinking the very basic concepts of traditional data exchange, such as solution, universal solution, and the certain answers of target queries. We develop a framework for data exchange over probabilistic databases, and make a case for its coherence and robustness. This framework applies to arbitrary schema mappings, and finite or countably infinite probability spaces on the source and target instances. After establishing this framework and formulating the key concepts, we study the application of the framework to a concrete and practical setting where probabilistic databases are compactly encoded by means of annotations formulated over random Boolean variables. In this setting, we study the problems of testing for the existence of solutions and universal solutions, materializing such solutions, and evaluating target queries (for unions of conjunctive queries) in both the exact sense and the approximate sense. For each of the problems, we carry out a complexity analysis based on properties of the annotation, in various classes of dependencies. Finally, we show that the framework and results easily and completely generalize to allow not only the data, but also the schema mapping itself to be probabilistic.
Exploiting lineage for confidence computation in uncertain and probabilistic databases
, 2007
"... We study the problem of computing query results with confidence values in ULDBs: relational databases with uncertainty and lineage. ULDBs, which subsume probabilistic databases, offer an alternative decoupled method of computing confidence values: Instead of computing confidences during query proc ..."
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Cited by 40 (10 self)
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We study the problem of computing query results with confidence values in ULDBs: relational databases with uncertainty and lineage. ULDBs, which subsume probabilistic databases, offer an alternative decoupled method of computing confidence values: Instead of computing confidences during query processing, compute them afterwards based on lineage. This approach enables a wider space of query plans, and it permits selective computations when not all confidence values are needed. This paper develops a suite of algorithms and optimizations for a broad class of relational queries on ULDBs. We provide confidence computation algorithms for single data items, as well as efficient batch algorithms to compute confidences for an entire relation or database. All algorithms incorporate memoization to avoid redundant computations, and they have been implemented in the Trio prototype ULDB database system. Performance characteristics and scalability of the algorithms are demonstrated through experimental results over a large synthetic dataset. 1.
Worldset decompositions: Expressiveness and efficient algorithms
 In Proc. ICDT
, 2007
"... Abstract. Uncertain information is commonplace in realworld data management scenarios. The ability to represent large sets of possible instances (worlds) while supporting efficient storage and processing is an important challenge in this context. The recent formalism of worldset decompositions (WSD ..."
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Cited by 38 (12 self)
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Abstract. Uncertain information is commonplace in realworld data management scenarios. The ability to represent large sets of possible instances (worlds) while supporting efficient storage and processing is an important challenge in this context. The recent formalism of worldset decompositions (WSDs) provides a spaceefficient representation for uncertain data that also supports scalable processing. WSDs are complete for finite worldsets in that they can represent any finite set of possible worlds. For possibly infinite worldsets, we show that a natural generalization of WSDs precisely captures the expressive power of ctables. We then show that several important problems are efficiently solvable on WSDs while they are NPhard on ctables. Finally, we give a polynomialtime algorithm for factorizing WSDs, i.e. an efficient algorithm for minimizing such representations. 1
From Complete to Incomplete Information and Back
 In Proc. SIGMOD
"... Incomplete information arises naturally in numerous data management applications. Recently, several researchers have studied query processing in the context of incomplete information. Most work has combined the syntax of a traditional query language like relational algebra with a nonstandard semanti ..."
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Cited by 37 (11 self)
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Incomplete information arises naturally in numerous data management applications. Recently, several researchers have studied query processing in the context of incomplete information. Most work has combined the syntax of a traditional query language like relational algebra with a nonstandard semantics such as certain or ranked possible answers. There are now also languages with special features to deal with uncertainty. However, to the standards of the data management community, to date no language proposal has been made that can be considered a natural analog to SQL or relational algebra for the case of incomplete information. In this paper we propose such a language, Worldset Algebra, which satisfies the robustness criteria and analogies to relational algebra that we expect. The language supports the contemplation on alternatives and can thus map from a complete database to an incomplete one comprising several possible worlds. We show that Worldset Algebra is conservative over relational algebra in the sense that any query that maps from a complete database to a complete database (a completetocomplete query) is equivalent to a relational algebra query. Moreover, we give an efficient algorithm for effecting this translation. We then study algebraic query optimization of such queries. We argue that query languages with explicit constructs for handling uncertainty allow for the more natural and simple expression of many realworld decision support queries. The results of this paper not only suggest a language for specifying queries in this way, but also allow for their efficient evaluation in any relational database management system.
Approximate Lineage for Probabilistic Databases
"... In probabilistic databases, lineage is fundamental to both query processing and understanding the data. Current systems s.a. Trio or Mystiq use a complete approach in which the lineage for a tuple t is a Boolean formula which represents all derivations of t. In large databases lineage formulas can b ..."
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Cited by 34 (9 self)
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In probabilistic databases, lineage is fundamental to both query processing and understanding the data. Current systems s.a. Trio or Mystiq use a complete approach in which the lineage for a tuple t is a Boolean formula which represents all derivations of t. In large databases lineage formulas can become huge: in one public database (the Gene Ontology) we often observed 10MB of lineage (provenance) data for a single tuple. In this paper we propose to use approximate lineage, which is a much smaller formula keeping track of only the most important derivations, which the system can use to process queries and provide explanations. We discuss in detail two specific kinds of approximate lineage: (1) a conservative approximation called sufficient lineage that records the most important derivations for each tuple, and (2) polynomial lineage, which is more aggressive and can provide higher compression ratios, and which is based on Fourier approximations of Boolean expressions. In this paper we define approximate lineage formally, describe algorithms to compute approximate lineage and prove formally their error bounds, and validate our approach experimentally on a real data set. 1.