Proceedings of the 33rd ACM SIGMOD-SIGACT-SIGART symposium on Principles of database systems最新文献_第3页

Session details: Computing joins 会话详细信息:计算连接

Proceedings of the 33rd ACM SIGMOD-SIGACT-SIGART symposium on Principles of database systems Pub Date : 2014-06-18 DOI: 10.1145/3255788

Tony Tan

引用次数: 0

Expressiveness of guarded existential rule languages 守卫存在规则语言的表达性

Proceedings of the 33rd ACM SIGMOD-SIGACT-SIGART symposium on Principles of database systems Pub Date : 2014-06-18 DOI: 10.1145/2594538.2594556

G. Gottlob, S. Rudolph, M. Simkus

{"title":"Expressiveness of guarded existential rule languages","authors":"G. Gottlob, S. Rudolph, M. Simkus","doi":"10.1145/2594538.2594556","DOIUrl":"https://doi.org/10.1145/2594538.2594556","url":null,"abstract":"The so-called existential rules have recently gained attention, mainly due to their adequate expressiveness for ontological query answering. Several decidable fragments of such rules have been introduced, employing restriction such as various forms of guardedness to ensure decidability. Some of the more well-known languages in this arena are (weakly) guarded and (weakly) frontier-guarded fragments of existential rules. In this paper, we explore their relative and absolute expressiveness. In particular, we provide a new proof that queries expressed via frontier-guarded and guarded rules can be translated into plain Datalog queries. Since the converse translations are impossible, we develop generalizations of frontier-guarded and guarded rules to nearly frontier-guarded and nearly guarded rules, respectively, which have exactly the expressive power of Datalog. We further show that weakly frontier-guarded rules can be translated into weakly guarded rules, and thus, weakly frontier-guarded and weakly guarded rules have exactly the same expressive power. Such rules cannot be translated into Datalog since their query answering problem is ExpTime-complete in data complexity. We strengthen this result by showing that on ordered databases and with input negation available, weakly guarded rules capture all queries decidable in exponential time. We then show that weakly guarded rules extended with stratified negation are expressive enough to capture all database queries decidable in exponential time, without any assumptions about input databases. Finally, we note that the translations of this paper are, in general, exponential in size, but lead to worst-case optimal algorithms for query answering with considered languages.","PeriodicalId":302451,"journal":{"name":"Proceedings of the 33rd ACM SIGMOD-SIGACT-SIGART symposium on Principles of database systems","volume":"69 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2014-06-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"116295683","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 44

Model-data Ecosystems: challenges, tools, and trends 模型-数据生态系统:挑战、工具和趋势

Proceedings of the 33rd ACM SIGMOD-SIGACT-SIGART symposium on Principles of database systems Pub Date : 2014-06-18 DOI: 10.1145/2594538.2594562

P. Haas

引用次数: 3

Generating low-cost plans from proofs 从证明中生成低成本计划

Proceedings of the 33rd ACM SIGMOD-SIGACT-SIGART symposium on Principles of database systems Pub Date : 2014-06-18 DOI: 10.1145/2594538.2594550

Michael Benedikt, B. T. Cate, Efthymia Tsamoura

{"title":"Generating low-cost plans from proofs","authors":"Michael Benedikt, B. T. Cate, Efthymia Tsamoura","doi":"10.1145/2594538.2594550","DOIUrl":"https://doi.org/10.1145/2594538.2594550","url":null,"abstract":"We look at generating plans that answer queries over restricted interfaces, making use of information about source integrity constraints, access restrictions, and access costs. Our method can exploit the integrity constraints to find low-cost access plans even when there is no direct access to relations appearing in the query. The key idea of our method is to move from a search for a plan to a search for a proof that a query is answerable, and then emph{generate a plan from a proof}. Discovery of one proof allows us to find a single plan that answers the query; exploration of several alternative proofs allows us to find low-cost plans. We start by overviewing a correspondence between proofs and restricted-interface plans in the context of arbitrary first-order constraints, based on interpolation. The correspondence clarifies the connection between preservation and interpolation theorems and reformulation problems, while generalizing it in several dimensions. We then provide direct plan-generation algorithms for schemas based on tuple-generating dependencies. Finally, we show how the direct plan-generation approach can be adapted to take into account the cost of plans.","PeriodicalId":302451,"journal":{"name":"Proceedings of the 33rd ACM SIGMOD-SIGACT-SIGART symposium on Principles of database systems","volume":"14 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2014-06-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"126722135","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 27

Counting solutions to conjunctive queries: structural and hybrid tractability 联合查询的计数解决方案:结构和混合可追溯性

Proceedings of the 33rd ACM SIGMOD-SIGACT-SIGART symposium on Principles of database systems Pub Date : 2014-06-18 DOI: 10.1145/2594538.2594559

G. Greco, Francesco Scarcello

{"title":"Counting solutions to conjunctive queries: structural and hybrid tractability","authors":"G. Greco, Francesco Scarcello","doi":"10.1145/2594538.2594559","DOIUrl":"https://doi.org/10.1145/2594538.2594559","url":null,"abstract":"Counting the number of answers to conjunctive queries is an intractable problem, formally #P-hard, even over classes of acyclic queries. However, Durand and Mengel have recently introduced the notion of quantified star size that, combined with hypertree decompositions, identifies islands of tractability for the problem. They also wonder whether such a notion precisely characterizes those classes for which the counting problem is tractable. We show that this is the case only for bounded-arity simple queries, where relation symbols cannot be shared by different query atoms. Indeed, we give a negative answer to the question in the general case, by exhibiting a more powerful structural method based on the novel concept of #-generalized hypertree decomposition. On classes of queries with bounded #-generalized hypertree width, counting answers is shown to be feasible in polynomial time, after a fixed-parameter polynomial-time preprocessing that only depends on the query structure. A weaker variant (but still more general than the technique based on the quantified starsize) is also proposed, for which tractability is established without any exponential dependency on the query size. Based on #-generalized hypertree decompositions, a hybrid decomposition method is eventually conceived, where structural properties of the query are exploited in combination with properties of the given database, such as keys or other (weaker) dependencies among attributes that limit the allowed combinations of values. Intuitively, such features may induce different structural properties that are not identified by the worst-possible database perspective of purely structural methods.","PeriodicalId":302451,"journal":{"name":"Proceedings of the 33rd ACM SIGMOD-SIGACT-SIGART symposium on Principles of database systems","volume":"15 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2014-06-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"126536458","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 19

Enumerating answers to first-order queries over databases of low degree 对低次数据库的一阶查询的枚举答案

Proceedings of the 33rd ACM SIGMOD-SIGACT-SIGART symposium on Principles of database systems Pub Date : 2014-06-18 DOI: 10.1145/2594538.2594539

Arnaud Durand, Nicole Schweikardt, L. Segoufin

引用次数: 36

Does query evaluation tractability help query containment? 查询求值可追溯性是否有助于查询包含?

Proceedings of the 33rd ACM SIGMOD-SIGACT-SIGART symposium on Principles of database systems Pub Date : 2014-06-18 DOI: 10.1145/2594538.2594553

P. Barceló, M. Romero, Moshe Y. Vardi

{"title":"Does query evaluation tractability help query containment?","authors":"P. Barceló, M. Romero, Moshe Y. Vardi","doi":"10.1145/2594538.2594553","DOIUrl":"https://doi.org/10.1145/2594538.2594553","url":null,"abstract":"While checking containment of Datalog programs is undecidable, checking whether a Datalog program is contained in a union of conjunctive queries (UCQ), in the context of relational databases, or a union of conjunctive 2-way regular path queries (UC2RPQ), in the context of graph databases, is decidable. The complexity of these problems is, however, prohibitive: 2exptime-complete. We investigate to which extent restrictions on UCQs and UC2RPQs, which have been known to reduce the complexity of query containment for these classes, yield a more \"manageable\" single-exponential time bound, which is the norm for several static analysis and verification tasks. Checking containment of a UCQ Theta' in a UCQ Theta is NP-hard, in general, but better bounds can be obtained if Theta is restricted to belong to a \"tractable\" class of UCQs, e.g., a class of bounded treewidth or hypertreewidth. Also, each Datalog program Pi is equivalent to an infinite union of CQs. This motivated us to study the question of whether restricting Theta to belong to a tractable class also helps alleviate the complexity of checking whether Pi is contained in Theta. We study such question in detail and show that the situation is much more delicate than expected: First, tractability of UCQs does not help in general, but further restricting Theta to be acyclic and have a bounded number of shared variables between atoms yields better complexity bounds. As corollaries, we obtain that checking containment of Pi in Theta is in exptime if Theta is of treewidth one, or it is acyclic and the arity of the schema is fixed. In the case of UC2RPQs we show an exptime bound when queries are acyclic and have a bounded number of edges connecting pairs of variables. As a corollary, we obtain that checking whether Pi is contained in UC2RPQ Gamma is in exptime if Gamma is a strongly acyclic UC2RPQ. Our positive results for UCQs and UC2RPQs are optimal, in a sense, since slightly extending the conditions turns the problem 2exptime-complete.","PeriodicalId":302451,"journal":{"name":"Proceedings of the 33rd ACM SIGMOD-SIGACT-SIGART symposium on Principles of database systems","volume":"83 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2014-06-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"114238225","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 13

Containment and equivalence of well-designed SPARQL 良好设计的SPARQL的包容和等价性

Proceedings of the 33rd ACM SIGMOD-SIGACT-SIGART symposium on Principles of database systems Pub Date : 2014-06-18 DOI: 10.1145/2594538.2594542

R. Pichler, Sebastian Skritek

引用次数: 46

Session details: Tutorial 1 会话细节:教程1

Proceedings of the 33rd ACM SIGMOD-SIGACT-SIGART symposium on Principles of database systems Pub Date : 2014-06-18 DOI: 10.1145/3255783

J. V. D. Bussche

引用次数: 0

Skew in parallel query processing 并行查询处理中的倾斜

Proceedings of the 33rd ACM SIGMOD-SIGACT-SIGART symposium on Principles of database systems Pub Date : 2014-01-08 DOI: 10.1145/2594538.2594558

P. Beame, Paraschos Koutris, Dan Suciu

{"title":"Skew in parallel query processing","authors":"P. Beame, Paraschos Koutris, Dan Suciu","doi":"10.1145/2594538.2594558","DOIUrl":"https://doi.org/10.1145/2594538.2594558","url":null,"abstract":"We study the problem of computing a conjunctive query q in parallel, using p of servers, on a large database. We consider algorithms with one round of communication, and study the complexity of the communication. We are especially interested in the case where the data is skewed, which is a major challenge for scalable parallel query processing. We establish a tight connection between the fractional edge packing of the query and the amount of communication in two cases. First, in the case when the only statistics on the database are the cardinalities of the input relations, and the data is skew-free, we provide matching upper and lower bounds (up to a polylogarithmic factor of p) expressed in terms of fractional edge packings of the query q. Second, in the case when the relations are skewed and the heavy hitters and their frequencies are known, we provide upper and lower bounds expressed in terms of packings of residual queries obtained by specializing the query to a heavy hitter. All our lower bounds are expressed in the strongest form, as number of bits needed to be communicated between processors with unlimited computational power. Our results generalize prior results on uniform databases (where each relation is a matching) [4], and lower bounds for the MapReduce model [1].","PeriodicalId":302451,"journal":{"name":"Proceedings of the 33rd ACM SIGMOD-SIGACT-SIGART symposium on Principles of database systems","volume":"175 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2014-01-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"127661418","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

引用次数: 126