ACM Transactions on Database Systems最新文献

{"title":"Partial Evaluation for Distributed XPath Query Processing and Beyond","authors":"G. Cong, W. Fan, Anastasios Kementsietsidis, Jianzhong Li, Xianmin Liu","doi":"10.1145/2389241.2389251","DOIUrl":"https://doi.org/10.1145/2389241.2389251","url":null,"abstract":"This article proposes algorithms for evaluating XPath queries over an XML tree that is partitioned horizontally and vertically, and is distributed across a number of sites. The key idea is based on partial evaluation: it is to send the whole query to each site that partially evaluates the query, in parallel, and sends the results as compact (Boolean) functions to a coordinator that combines these to obtain the result. This approach possesses the following performance guarantees. First, each site is visited at most twice for data-selecting XPath queries, and only once for Boolean XPath queries. Second, the network traffic is determined by the answer to the query, rather than the size of the tree. Third, the total computation is comparable to that of centralized algorithms on the tree stored in a single site, regardless of how the tree is fragmented and distributed. We also present a MapReduce algorithm for evaluating Boolean XPath queries, based on partial evaluation. In addition, we provide algorithms to evaluate XPath queries on very large XML trees, in a centralized setting. We show both analytically and empirically that our techniques are scalable with large trees and complex XPath queries. These results, we believe, illustrate the usefulness and potential of partial evaluation in distributed systems as well as centralized XML stores for evaluating XPath queries and beyond.","PeriodicalId":50915,"journal":{"name":"ACM Transactions on Database Systems","volume":"38 1","pages":"32:1-32:43"},"PeriodicalIF":1.8,"publicationDate":"2012-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"73043078","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"计算机科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Multiple Radii DisC Diversity: Result Diversification Based on Dissimilarity and Coverage","authors":"Marina Drosou, E. Pitoura","doi":"10.1145/2699499","DOIUrl":"https://doi.org/10.1145/2699499","url":null,"abstract":"Recently, result diversification has attracted a lot of attention as a means to improve the quality of results retrieved by user queries. In this article, we introduce a novel definition of diversity called DisC diversity. Given a tuning parameter r, which we call radius, we consider two items to be similar if their distance is smaller than or equal to r. A DisC diverse subset of a result contains items such that each item in the result is represented by a similar item in the diverse subset and the items in the diverse subset are dissimilar to each other. We show that locating a minimum DisC diverse subset is an NP-hard problem and provide algorithms for its approximation. We extend our definition to the multiple radii case, where each item is associated with a different radius based on its importance, relevance, or other factors. We also propose adapting DisC diverse subsets to a different degree of diversification by adjusting r, that is, increasing the radius (or zooming-out) and decreasing the radius (or zooming-in). We present efficient implementations of our algorithms based on the M-tree, a spatial index structure, and experimentally evaluate their performance.","PeriodicalId":50915,"journal":{"name":"ACM Transactions on Database Systems","volume":"37 1","pages":"4:1-4:43"},"PeriodicalIF":1.8,"publicationDate":"2012-08-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"73236498","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"计算机科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Efficient reasoning about data trees via integer linear programming","authors":"C. David, L. Libkin, Tony Tan","doi":"10.1145/2338626.2338632","DOIUrl":"https://doi.org/10.1145/2338626.2338632","url":null,"abstract":"Data trees provide a standard abstraction of XML documents with data values: they are trees whose nodes, in addition to the usual labels, can carry labels from an infinite alphabet (data). Therefore, one is interested in decidable formalisms for reasoning about data trees. While some are known—such as the two-variable logic—they tend to be of very high complexity, and most decidability proofs are highly nontrivial. We are therefore interested in reasonable complexity formalisms as well as better techniques for proving decidability.\u0000 Here we show that many decidable formalisms for data trees are subsumed—fully or partially—by the power of tree automata together with set constraints and linear constraints on cardinalities of various sets of data values. All these constraints can be translated into instances of integer linear programming, giving us an NP upper bound on the complexity of the reasoning tasks. We prove that this bound, as well as the key encoding technique, remain very robust, and allow the addition of features such as counting of paths and patterns, and even a concise encoding of constraints, without increasing the complexity. The NP bound is tight, as we also show that the satisfiability of a single set constraint is already NP-hard.\u0000 We then relate our results to several reasoning tasks over XML documents, such as satisfiability of schemas and data dependencies and satisfiability of the two-variable logic. As a final contribution, we describe experimental results based on the implementation of some reasoning tasks using the SMT solver Z3.","PeriodicalId":50915,"journal":{"name":"ACM Transactions on Database Systems","volume":"27 1","pages":"19:1-19:28"},"PeriodicalIF":1.8,"publicationDate":"2012-08-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"74575268","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"计算机科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Artifact systems with data dependencies and arithmetic","authors":"Elio Damaggio, Alin Deutsch, V. Vianu","doi":"10.1145/2338626.2338628","DOIUrl":"https://doi.org/10.1145/2338626.2338628","url":null,"abstract":"We study the static verification problem for data-centric business processes, specified in a variant of IBM's “business artifact” model. Artifacts are records of variables that correspond to business-relevant objects and are updated by a set of services equipped with pre- and postconditions, that implement business process tasks. The verification problem consists in statically checking whether all runs of an artifact system satisfy desirable properties expressed in a first-order extension of linear-time temporal logic. Previous work identified the class of guarded artifact systems and properties, for which verification is decidable. However, the results suffer an important limitation: they fail in the presence of even very simple data dependencies or arithmetic, both crucial to real-life business processes. In this article, we extend the artifact model and verification results to alleviate this limitation. We identify a practically significant class of business artifacts with data dependencies and arithmetic, for which verification is decidable. The technical machinery needed to establish the results is fundamentally different from previous work. While the worst-case complexity of verification is nonelementary, we identify various realistic restrictions yielding more palatable upper bounds.","PeriodicalId":50915,"journal":{"name":"ACM Transactions on Database Systems","volume":"22 1","pages":"22:1-22:36"},"PeriodicalIF":1.8,"publicationDate":"2012-08-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"81443521","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"计算机科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Foster b-trees","authors":"G. Graefe, Hideaki Kimura, Harumi A. Kuno","doi":"10.1145/2338626.2338630","DOIUrl":"https://doi.org/10.1145/2338626.2338630","url":null,"abstract":"Foster B-trees are a new variant of B-trees that combines advantages of prior B-tree variants optimized for many-core processors and modern memory hierarchies with flash storage and nonvolatile memory. Specific goals include: (i) minimal concurrency control requirements for the data structure, (ii) efficient migration of nodes to new storage locations, and (iii) support for continuous and comprehensive self-testing. Like Blink-trees, Foster B-trees optimize latching without imposing restrictions or specific designs on transactional locking, for example, key range locking. Like write-optimized B-trees, and unlike Blink-trees, Foster B-trees enable large writes on RAID and flash devices as well as wear leveling and efficient defragmentation. Finally, they support continuous and inexpensive yet comprehensive verification of all invariants, including all cross-node invariants of the B-tree structure. An implementation and a performance evaluation show that the Foster B-tree supports high concurrency and high update rates without compromising consistency, correctness, or read performance.","PeriodicalId":50915,"journal":{"name":"ACM Transactions on Database Systems","volume":"64 1","pages":"17:1-17:29"},"PeriodicalIF":1.8,"publicationDate":"2012-08-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"72876997","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"计算机科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Reordering rows for better compression: Beyond the lexicographic order","authors":"D. Lemire, Owen Kaser, E. Gutarra","doi":"10.1145/2338626.2338633","DOIUrl":"https://doi.org/10.1145/2338626.2338633","url":null,"abstract":"Sorting database tables before compressing them improves the compression rate. Can we do better than the lexicographical order? For minimizing the number of runs in a run-length encoding compression scheme, the best approaches to row-ordering are derived from traveling salesman heuristics, although there is a significant trade-off between running time and compression. A new heuristic, Multiple Lists, which is a variant on Nearest Neighbor that trades off compression for a major running-time speedup, is a good option for very large tables. However, for some compression schemes, it is more important to generate long runs rather than few runs. For this case, another novel heuristic, Vortex, is promising. We find that we can improve run-length encoding up to a factor of 3 whereas we can improve prefix coding by up to 80%: these gains are on top of the gains due to lexicographically sorting the table. We prove that the new row reordering is optimal (within 10%) at minimizing the runs of identical values within columns, in a few cases.","PeriodicalId":50915,"journal":{"name":"ACM Transactions on Database Systems","volume":"53 10 1","pages":"16:1"},"PeriodicalIF":1.8,"publicationDate":"2012-07-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"87667568","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"计算机科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Stochastic skylines","authors":"W. Zhang, Xuemin Lin, Ying Zhang, M. A. Cheema, Qing Zhang","doi":"10.1145/2188349.2188356","DOIUrl":"https://doi.org/10.1145/2188349.2188356","url":null,"abstract":"In many applications involving multiple criteria optimal decision making, users may often want to make a personal trade-off among all optimal solutions for selecting one object that fits best their personal needs. As a key feature, the skyline in a multidimensional space provides the minimum set of candidates for such purposes by removing all points not preferred by any (monotonic) utility/scoring functions; that is, the skyline removes all objects not preferred by any user no matter how their preferences vary. Driven by many recent applications with uncertain data, the probabilistic skyline model is proposed to retrieve uncertain objects based on skyline probabilities. Nevertheless, skyline probabilities cannot capture the preferences of monotonic utility functions. Motivated by this, in this article we propose a novel skyline operator, namely stochastic skylines. In the light of the expected utility principle, stochastic skylines guarantee to provide the minimum set of candidates to optimal solutions over a family of utility functions. We first propose the lskyline operator based on the lower orthant orders. lskyline guarantees to provide the minimum set of candidates to the optimal solutions for the family of monotonic multiplicative utility functions. While lskyline works very effectively for the family of multiplicative functions, it may miss optimal solutions for other utility /scoring functions (e.g., linear functions). To resolve this, we also propose a general stochastic skyline operator, gskyline, based on the usual orders. gskyline provides the minimum candidate set to the optimal solutions for all monotonic functions. For the first time regarding the existing literature, we investigate the complexities of determining a stochastic order between two uncertain objects whose probability distributions are described discretely. We firstly show that determining the lower orthant order is NP-complete with respect to the dimensionality; consequently the problem of computing lskyline is NP-complete. We also show an interesting result as follows. While the usual order involves more complicated geometric forms than the lower orthant order, the usual order may be determined in polynomial time regarding all the inputs, including the dimensionality; this implies that gskyline can be computed in polynomial time. A general framework is developed for efficiently and effectively retrieving lskyline and gskyline from a set of uncertain objects, respectively, together with efficient and effective filtering techniques. Novel and efficient verification algorithms are developed to efficiently compute lskyline over multidimensional uncertain data, which run in polynomial time if the dimensionality is fixed, and to efficiently compute gskyline in polynomial time regarding all inputs. We also show, by theoretical analysis and experiments, that the sizes of lskyline and gskyline are both quite similar to that of conventional skyline over certain data. Comprehens","PeriodicalId":50915,"journal":{"name":"ACM Transactions on Database Systems","volume":"39 1","pages":"14:1-14:34"},"PeriodicalIF":1.8,"publicationDate":"2012-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"77982365","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"计算机科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Exact and approximate algorithms for the most connected vertex problem","authors":"Cheng Sheng, Yufei Tao, Jianzhong Li","doi":"10.1145/2188349.2188354","DOIUrl":"https://doi.org/10.1145/2188349.2188354","url":null,"abstract":"An <i>(edge) hidden graph</i> is a graph whose edges are notexplicitly given. Detecting the presence of an edge requires an expensive edge probing query. We consider the <i>k Most Connected Vertex</i> (<i>k</i>-MCV) problem on hidden bipartite graphs. Given a bipartite graph <i>G</i> with independent vertex sets <i>B</i> and <i>W</i>, the goal is to find the <i>k</i> vertices in <i>B</i> with the largest degrees using the minimum number of queries. This problem can be regarded as a top-<i>k</i> extension of semi-join, and is encountered in several applications in practice.\u0000 If <i>B</i> and <i>W</i> have <i>n</i> and <i>m</i> vertices, respectively, the number of queries needed to solve the problem is <i>nm</i> in the worst case. This, however, is a pessimistic estimate on how many queries are necessary on practical data. In fact, on some inputs, the problem may be settled with only <i>km</i> + <i>n</i> queries, which is significantly lower than <i>nm</i> for <i>k</i> ≪ <i>n</i>. The huge difference between <i>km</i> + <i>n</i> and <i>nm</i> makes it interesting to design an adaptive algorithm that is guaranteed to achieve the best possible performance on every input <i>G</i>. For <i>k</i> ≤ <i>n</i>/2, we give an algorithm that is instance optimal among a broad class of solutions. This means that, for any <i>G</i>, our algorithm can perform more queries than the optimal solution (which is unknown) by only a constant factor, which can be shown at most 2.\u0000 As a second step, we study an ϵ-approximate version of the <i>k</i>-MCV problem, where ϵ is a parameter satisfying 0 < ϵ < 1. The goal is to return <i>k</i> black vertices <i>b</i>₁, …, <i>b_k</i> such that the degree of <i>b_i</i> (<i>i</i> ≤ <i>k</i>) can be smaller than <i>t</i>_<i>i</i> by a factor of at most ϵ, where <i>t</i>_<i>i</i>, …, <i>t</i>_<i>k</i> (in nonascending order) are the degrees of the <i>k</i> most connected black vertices. We give an efficient randomized algorithm that successfully finds the correct answer with high probability. In particular, for a fixed ϵ and a fixed success probability, our algorithm performs <i>o(nm)</i> queries in expectation for <i>t</i>_<i>k</i> = ω(log <i>n</i>). In other words, whenever <i>t</i>_<i>k</i> is greater than log <i>n</i> by more than a constant, our algorithm beats the Ω(<i>nm</i>) lower bound for solving the <i>k</i>-MCV problem exactly. All the proposed algorithms, despite the complication of their underlying theory, are simple enough for easy implementation in practice. Extensive experiments have confirmed that their performance in reality agrees with our theoretical findings very well.","PeriodicalId":50915,"journal":{"name":"ACM Transactions on Database Systems","volume":"38 1","pages":"12:1-12:39"},"PeriodicalIF":1.8,"publicationDate":"2012-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"83558182","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"计算机科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Secure distributed computation of anonymized views of shared databases","authors":"Tamir Tassa, E. Gudes","doi":"10.1145/2188349.2188353","DOIUrl":"https://doi.org/10.1145/2188349.2188353","url":null,"abstract":"We consider the problem of computing efficient anonymizations of partitioned databases. Given a database that is partitioned between several sites, either horizontally or vertically, we devise secure distributed algorithms that allow the different sites to obtain a k-anonymized and ℓ-diverse view of the union of their databases, without disclosing sensitive information. Our algorithms are based on the sequential algorithm [Goldberger and Tassa 2010] that offers anonymizations with utility that is significantly better than other anonymization algorithms, and in particular those that were implemented so far in the distributed setting. Our algorithms can apply to different generalization techniques and utility measures and to any number of sites. While previous distributed algorithms depend on costly cryptographic primitives, the cryptographic assumptions of our solution are surprisingly minimal.","PeriodicalId":50915,"journal":{"name":"ACM Transactions on Database Systems","volume":"116 1","pages":"11:1-11:43"},"PeriodicalIF":1.8,"publicationDate":"2012-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"89304727","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"计算机科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"The implication problem of data dependencies over SQL table definitions: Axiomatic, algorithmic and logical characterizations","authors":"Sven Hartmann, S. Link","doi":"10.1145/2188349.2188355","DOIUrl":"https://doi.org/10.1145/2188349.2188355","url":null,"abstract":"We investigate the implication problem for classes of data dependencies over SQL table definitions. Under Zaniolo's “no information” interpretation of null markers we establish an axiomatization and algorithms to decide the implication problem for the combined class of functional and multivalued dependencies in the presence of NOT NULL constraints. The resulting theory subsumes three previously orthogonal frameworks. We further show that the implication problem of this class is equivalent to that in a propositional fragment of Schaerf and Cadoli's [1995] family of para-consistent S-3 logics. In particular, S is the set of variables that correspond to attributes declared NOT NULL. We also show how our equivalences for multivalued dependencies can be extended to Delobel's class of full first-order hierarchical decompositions, and the equivalences for functional dependencies can be extended to arbitrary Boolean dependencies. These dualities allow us to transfer several findings from the propositional fragments to the corresponding classes of data dependencies, and vice versa. We show that our results also apply to Codd's null interpretation “value unknown at present”, but not to Imielinski's [1989] or-relations utilizing Levene and Loizou's weak possible world semantics [Levene and Loizou 1998]. Our findings establish NOT NULL constraints as an effective mechanism to balance not only the certainty in database relations but also the expressiveness with the efficiency of entailment relations. They also control the degree by which the implication of data dependencies over total relations is soundly approximated in SQL table definitions.","PeriodicalId":50915,"journal":{"name":"ACM Transactions on Database Systems","volume":"67 1","pages":"13:1-13:40"},"PeriodicalIF":1.8,"publicationDate":"2012-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"81002171","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"计算机科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}