ACM Transactions on Database Systems最新文献

{"title":"Static analysis and optimization of semantic web queries","authors":"Andrés Letelier, Jorge Pérez, R. Pichler, Sebastian Skritek","doi":"10.1145/2500130","DOIUrl":"https://doi.org/10.1145/2500130","url":null,"abstract":"Static analysis is a fundamental task in query optimization. In this article we study static analysis and optimization techniques for SPARQL, which is the standard language for querying Semantic Web data. Of particular interest for us is the optionality feature in SPARQL. It is crucial in Semantic Web data management, where data sources are inherently incomplete and the user is usually interested in partial answers to queries. This feature is one of the most complicated constructors in SPARQL and also the one that makes this language depart from classical query languages such as relational conjunctive queries. We focus on the class of well-designed SPARQL queries, which has been proposed in the literature as a fragment of the language with good properties regarding query evaluation. We first propose a tree representation for SPARQL queries, called pattern trees, which captures the class of well-designed SPARQL graph patterns. Among other results, we propose several rules that can be used to transform pattern trees into a simple normal form, and study equivalence and containment. We also study the evaluation and enumeration problems for this class of queries.","PeriodicalId":50915,"journal":{"name":"ACM Transactions on Database Systems","volume":null,"pages":null},"PeriodicalIF":1.8,"publicationDate":"2013-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"78473638","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":"Consistent thinning of large geographical data for map visualization","authors":"A. Sarma, Hongrae Lee, Hector Gonzalez, J. Madhavan, A. Halevy","doi":"10.1145/2539032.2539034","DOIUrl":"https://doi.org/10.1145/2539032.2539034","url":null,"abstract":"Large-scale map visualization systems play an increasingly important role in presenting geographic datasets to end-users. Since these datasets can be extremely large, a map rendering system often needs to select a small fraction of the data to visualize them in a limited space. This article addresses the fundamental challenge of thinning: determining appropriate samples of data to be shown on specific geographical regions and zoom levels. Other than the sheer scale of the data, the thinning problem is challenging because of a number of other reasons: (1) data can consist of complex geographical shapes, (2) rendering of data needs to satisfy certain constraints, such as data being preserved across zoom levels and adjacent regions, and (3) after satisfying the constraints, an optimal solution needs to be chosen based on objectives such as maximality, fairness, and importance of data.\u0000 This article formally defines and presents a complete solution to the thinning problem. First, we express the problem as an integer programming formulation that efficiently solves thinning for desired objectives. Second, we present more efficient solutions for maximality, based on DFS traversal of a spatial tree. Third, we consider the common special case of point datasets, and present an even more efficient randomized algorithm. Fourth, we show that contiguous regions are tractable for a general version of maximality for which arbitrary regions are intractable. Fifth, we examine the structure of our integer programming formulation and show that for point datasets, our program is integral. Finally, we have implemented all techniques from this article in Google Maps [Google 2005] visualizations of fusion tables [Gonzalez et al. 2010], and we describe a set of experiments that demonstrate the trade-offs among the algorithms.","PeriodicalId":50915,"journal":{"name":"ACM Transactions on Database Systems","volume":null,"pages":null},"PeriodicalIF":1.8,"publicationDate":"2013-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"78969822","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":"High-performance complex event processing over hierarchical data","authors":"Barzan Mozafari, Kai Zeng, Loris D'antoni, C. Zaniolo","doi":"10.1145/2536779","DOIUrl":"https://doi.org/10.1145/2536779","url":null,"abstract":"While Complex Event Processing (CEP) constitutes a considerable portion of the so-called Big Data analytics, current CEP systems can only process data having a simple structure, and are otherwise limited in their ability to efficiently support complex continuous queries on structured or semistructured information. However, XML-like streams represent a very popular form of data exchange, comprising large portions of social network and RSS feeds, financial feeds, configuration files, and similar applications requiring advanced CEP queries. In this article, we present the XSeq language and system that support CEP on XML streams, via an extension of XPath that is both powerful and amenable to an efficient implementation. Specifically, the XSeq language extends XPath with natural operators to express sequential and Kleene-* patterns over XML streams, while remaining highly amenable to efficient execution. In fact, XSeq is designed to take full advantage of the recently proposed Visibly Pushdown Automata (VPA), where higher expressive power can be achieved without compromising the computationally attractive properties of finite state automata. Besides the efficiency and expressivity benefits, the choice of VPA as the underlying model also enables XSeq to go beyond XML streams and be easily applicable to any data with both sequential and hierarchical structures, including JSON messages, RNA sequences, and software traces. Therefore, we illustrate the XSeq's power for CEP applications through examples from different domains and provide formal results on its expressiveness and complexity. Finally, we present several optimization techniques for XSeq queries. Our extensive experiments indicate that XSeq brings outstanding performance to CEP applications: two orders of magnitude improvement is obtained over the same queries executed in general-purpose XML engines.","PeriodicalId":50915,"journal":{"name":"ACM Transactions on Database Systems","volume":null,"pages":null},"PeriodicalIF":1.8,"publicationDate":"2013-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"75550230","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":"Validating XML documents in the streaming model with external memory","authors":"C. Konrad, F. Magniez","doi":"10.1145/2504590","DOIUrl":"https://doi.org/10.1145/2504590","url":null,"abstract":"We study the problem of validating XML documents of size N against general DTDs in the context of streaming algorithms. The starting point of this work is a well-known space lower bound. There are XML documents and DTDs for which p-pass streaming algorithms require Ω(N/p) space. We show that when allowing access to external memory, there is a deterministic streaming algorithm that solves this problem with memory space &Order;(log2 N), a constant number of auxiliary read/write streams, and &Order;(log N) total number of passes on the XML document and auxiliary streams. An important intermediate step of this algorithm is the computation of the First-Child-Next-Sibling (FCNS) encoding of the initial XML document in a streaming fashion. We study this problem independently, and we also provide memory-efficient streaming algorithms for decoding an XML document given in its FCNS encoding. Furthermore, validating XML documents encoding binary trees against any DTD in the usual streaming model without external memory can be done with sublinear memory. There is a one-pass algorithm using &Order;(√N log N) space, and a bidirectional two-pass algorithm using &Order;(log2 N) space which perform this task.","PeriodicalId":50915,"journal":{"name":"ACM Transactions on Database Systems","volume":null,"pages":null},"PeriodicalIF":1.8,"publicationDate":"2013-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"89108634","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":"Mergeable summaries","authors":"P. Agarwal, Graham Cormode, Zengfeng Huang, J. M. Phillips, Zhewei Wei, K. Yi","doi":"10.1145/2500128","DOIUrl":"https://doi.org/10.1145/2500128","url":null,"abstract":"We study the mergeability of data summaries. Informally speaking, mergeability requires that, given two summaries on two datasets, there is a way to merge the two summaries into a single summary on the two datasets combined together, while preserving the error and size guarantees. This property means that the summaries can be merged in a way akin to other algebraic operators such as sum and max, which is especially useful for computing summaries on massive distributed data. Several data summaries are trivially mergeable by construction, most notably all the sketches that are linear functions of the datasets. But some other fundamental ones, like those for heavy hitters and quantiles, are not (known to be) mergeable. In this article, we demonstrate that these summaries are indeed mergeable or can be made mergeable after appropriate modifications. Specifically, we show that for ϵ-approximate heavy hitters, there is a deterministic mergeable summary of size O(1/ϵ); for ϵ-approximate quantiles, there is a deterministic summary of size O((1/ϵ) log(ϵ n)) that has a restricted form of mergeability, and a randomized one of size O((1/ϵ) log3/2(1/ϵ)) with full mergeability. We also extend our results to geometric summaries such as ϵ-approximations which permit approximate multidimensional range counting queries. While most of the results in this article are theoretical in nature, some of the algorithms are actually very simple and even perform better than the previously best known algorithms, which we demonstrate through experiments in a simulated sensor network.\u0000 We also achieve two results of independent interest: (1) we provide the best known randomized streaming bound for ϵ-approximate quantiles that depends only on ϵ, of size O((1/ϵ) log3/2(1/ϵ)), and (2) we demonstrate that the MG and the SpaceSaving summaries for heavy hitters are isomorphic.","PeriodicalId":50915,"journal":{"name":"ACM Transactions on Database Systems","volume":null,"pages":null},"PeriodicalIF":1.8,"publicationDate":"2013-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"87896232","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":"Incremental graph pattern matching","authors":"Wenfei Fan, Xin Wang, Yinghui Wu","doi":"10.1145/2489791","DOIUrl":"https://doi.org/10.1145/2489791","url":null,"abstract":"Graph pattern matching is commonly used in a variety of emerging applications such as social network analysis. These applications highlight the need for studying the following two issues. First, graph pattern matching is traditionally defined in terms of subgraph isomorphism or graph simulation. These notions, however, often impose too strong a topological constraint on graphs to identify meaningful matches. Second, in practice a graph is typically large, and is frequently updated with small changes. It is often prohibitively expensive to recompute matches starting from scratch via batch algorithms when the graph is updated.\u0000 This article studies these two issues. (1) We propose to define graph pattern matching based on a notion of bounded simulation, which extends graph simulation by specifying the connectivity of nodes in a graph within a predefined number of hops. We show that bounded simulation is able to find sensible matches that the traditional matching notions fail to catch. We also show that matching via bounded simulation is in cubic time, by giving such an algorithm. (2) We provide an account of results on incremental graph pattern matching, for matching defined with graph simulation, bounded simulation, and subgraph isomorphism. We show that the incremental matching problem is unbounded, that is, its cost is not determined alone by the size of the changes in the input and output, for all these matching notions. Nonetheless, when matching is defined in terms of simulation or bounded simulation, incremental matching is semibounded, that is, its worst-time complexity is bounded by a polynomial in the size of the changes in the input, output, and auxiliary information that is necessarily maintained to reuse previous computation, and the size of graph patterns. We also develop incremental matching algorithms for graph simulation and bounded simulation, by minimizing unnecessary recomputation. In contrast, matching based on subgraph isomorphism is neither bounded nor semibounded. (3) We experimentally verify the effectiveness and efficiency of these algorithms, and show that: (a) the revised notion of graph pattern matching allows us to identify communities commonly found in real-life networks, and (b) the incremental algorithms substantially outperform their batch counterparts in response to small changes. These suggest a promising framework for real-life graph pattern matching.","PeriodicalId":50915,"journal":{"name":"ACM Transactions on Database Systems","volume":null,"pages":null},"PeriodicalIF":1.8,"publicationDate":"2013-08-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"85079316","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":"Algebraic incremental maintenance of XML views","authors":"A. Bonifati, M. Goodfellow, I. Manolescu, Domenica Sileo","doi":"10.1145/2508020.2508021","DOIUrl":"https://doi.org/10.1145/2508020.2508021","url":null,"abstract":"Materialized views can bring important performance benefits when querying XML documents. In the presence of XML document changes, materialized views need to be updated to faithfully reflect the changed document. In this work, we present an algebraic approach for propagating source updates to XML materialized views expressed in a powerful XML tree pattern formalism. Our approach differs from the state-of-the-art in the area in two important ways. First, it relies on set-oriented, algebraic operations, to be contrasted with node-based previous approaches. Second, it exploits state-of-the-art features of XML stores and XML query evaluation engines, notably XML structural identifiers and associated structural join algorithms. We present algorithms for determining how updates should be propagated to views, and highlight the benefits of our approach over existing algorithms through a series of experiments.","PeriodicalId":50915,"journal":{"name":"ACM Transactions on Database Systems","volume":null,"pages":null},"PeriodicalIF":1.8,"publicationDate":"2013-08-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"76420974","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":"Flexible and extensible preference evaluation in database systems","authors":"Justin J. Levandoski, A. Eldawy, M. Mokbel, Mohamed E. Khalefa","doi":"10.1145/2493268","DOIUrl":"https://doi.org/10.1145/2493268","url":null,"abstract":"Personalized database systems give users answers tailored to their personal preferences. While numerous preference evaluation methods for databases have been proposed (e.g., skyline, top-k, k-dominance, k-frequency), the implementation of these methods at the core of a database system is a double-edged sword. Core implementation provides efficient query processing for arbitrary database queries, however, this approach is not practical since each existing (and future) preference method requires implementation within the database engine. To solve this problem, this article introduces FlexPref, a framework for extensible preference evaluation in database systems. FlexPref, implemented in the query processor, aims to support a wide array of preference evaluation methods in a single extensible code base. Integration with FlexPref is simple, involving the registration of only three functions that capture the essence of the preference method. Once integrated, the preference method “lives” at the core of the database, enabling the efficient execution of preference queries involving common database operations. This article also provides a query optimization framework for FlexPref, as well as a theoretical framework that defines the properties a preference method must exhibit to be implemented in FlexPref. To demonstrate the extensibility of FlexPref, this article also provides case studies detailing the implementation of seven state-of-the-art preference evaluation methods within FlexPref. We also experimentally study the strengths and weaknesses of an implementation of FlexPref in PostgreSQL over a range of single-table and multitable preference queries.","PeriodicalId":50915,"journal":{"name":"ACM Transactions on Database Systems","volume":null,"pages":null},"PeriodicalIF":1.8,"publicationDate":"2013-08-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"89286713","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":"Collaborative data sharing via update exchange and provenance","authors":"G. Karvounarakis, Todd J. Green, Z. Ives, V. Tannen","doi":"10.1145/2500127","DOIUrl":"https://doi.org/10.1145/2500127","url":null,"abstract":"Recent work [Ives et al. 2005] proposed a new class of systems for supporting data sharing among scientific and other collaborations: this new collaborative data sharing system connects heterogeneous logical peers using a network of schema mappings. Each peer has a locally controlled and edited database instance, but wants to incorporate related data from other peers as well. To achieve this, every peer's data and updates propagate along the mappings to the other peers. However, this operation, termed update exchange, is filtered by trust conditions—expressing what data and sources a peer judges to be authoritative—which may cause a peer to reject another's updates. In order to support such filtering, updates carry provenance information.\u0000 This article develops methods for realizing such systems: we build upon techniques from data integration, data exchange, incremental view maintenance, and view update to propagate updates along mappings, both to derived and optionally to source instances. We incorporate a novel model for tracking data provenance, such that curators may filter updates based on trust conditions over this provenance. We implement our techniques in a layer above an off-the-shelf RDBMS, and we experimentally demonstrate the viability of these techniques in the Orchestra prototype system.","PeriodicalId":50915,"journal":{"name":"ACM Transactions on Database Systems","volume":null,"pages":null},"PeriodicalIF":1.8,"publicationDate":"2013-08-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"79948417","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":"Asymmetric signature schemes for efficient exact edit similarity query processing","authors":"Jianbin Qin, Wei Wang, Chuan Xiao, Yifei Lu, Xuemin Lin, Haixun Wang","doi":"10.1145/2508020.2508023","DOIUrl":"https://doi.org/10.1145/2508020.2508023","url":null,"abstract":"Given a query string Q, an edit similarity search finds all strings in a database whose edit distance with Q is no more than a given threshold τ. Most existing methods answering edit similarity queries employ schemes to generate string subsequences as signatures and generate candidates by set overlap queries on query and data signatures.\u0000 In this article, we show that for any such signature scheme, the lower bound of the minimum number of signatures is τ + 1, which is lower than what is achieved by existing methods. We then propose several asymmetric signature schemes, that is, extracting different numbers of signatures for the data and query strings, which achieve this lower bound. A basic asymmetric scheme is first established on the basis of matching q-chunks and q-grams between two strings. Two efficient query processing algorithms (IndexGram and IndexChunk) are developed on top of this scheme. We also propose novel candidate pruning methods to further improve the efficiency. We then generalize the basic scheme by incorporating novel ideas of floating q-chunks, optimal selection of q-chunks, and reducing the number of signatures using global ordering. As a result, the Super and Turbo families of schemes are developed together with their corresponding query processing algorithms. We have conducted a comprehensive experimental study using the six asymmetric algorithms and nine previous state-of-the-art algorithms. The experiment results clearly showcase the efficiency of our methods and demonstrate space and time characteristics of our proposed algorithms.","PeriodicalId":50915,"journal":{"name":"ACM Transactions on Database Systems","volume":null,"pages":null},"PeriodicalIF":1.8,"publicationDate":"2013-08-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"76222665","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}