Alon Y. Levy, Anand Rajaraman, and Jeffrey D. Ullman. Answering queries using limited external processors. In Proceedings of the 15th ACM SIGACT-SIGMOD-SIGART Symposium on Principles of Database Systems, Montreal, Canada, 1996.  Home/Search   Document Not in Database   Summary   Related Articles   Check

....of different sources change at different rates, making the data warehousing approach to integration hard to develop and maintain. In addition, Web sources may not provide their full data in advance. The platform we describe resolves this challenge by being based on the on demand mediator approach [49, 9, 34, 7, 46, 29]: information is collected dynamically from the sources, in response to application requests. The Mediator, which is the query processing core of the EXIP platform, has to decompose application requests into an efficient series of requests targeted to the sources. These requests have to be ....

.... integration systems was extended to include the integration of autonomous and non structured sources and the mediator concept was created [49] EXIP follows the architecture of earlier virtual view mediators, such as TSIMMIS [20] YAT [9] HERMES [46] Garlic [7] and the Information Manifold [29]. XAlgebra is the cornerstone of query processing in EXIP, similarly to the roles that algebras play in relational [21] and object oriented databases [12] Algebras were also designed for the nested relational [42] and complex value models [1] Recently XML Query Algebras have been proposed as ....

A. Levy, A. Rajaraman, and J. Ullman. Answering queries using limited external processors. In Proc. PODS, pages 237--37, 1996.

....which can combine interactive computational abstractions for data access. For this reason we can say that our contribution is original and complementary to the works known in the literature on interactive data access. With respect to the semantics of complex services in service algebra, the work [16] deal with the problem of the expressive power of querying a limited set of views. This could be applied to the service algebra, providing a theoretical framework to determine the expressive power of the algebraic combination of services, given a fixed set of initial services. 6. CONCLUSIONS ....

A.Y. Levy, A. Rajaraman, and J.D. Ullman. Answering queries using limited external processors.# ############ ### #### ## ## ####################################################################, Montreal, Canada, pp. 227-237 (1996).

....consider the rewriting problem in the case where the query can create answer trees, and queries do not involve regular path expressions with recursion. In nite number of views: Two works have considered the problem of answering queries using views in the presence of an in nite number of views [37, 44]. The motivation for this seemingly curious problem is that when a data source has the capability to perform local processing, it can be modeled by a (possibly in nite) set of views it can supply, rather than a single one. Hence, to answer queries using such sources, one need not only choose ....

....local processing, it can be modeled by a (possibly in nite) set of views it can supply, rather than a single one. Hence, to answer queries using such sources, one need not only choose which sources to query, but also which query to send to it out of the set of possible queries it can answer. In [37, 44] it is shown that in certain important cases the problem of answering a query using an in nite set of views are decidable. Of particular note is the case in which the set of views that a source can answer is described by the nite unfoldings of a datalog program. Description Logics: Description ....

Alon Y. Levy, Anand Rajaraman, and Jerey D. Ullman. Answering queries using limited external processors. In Proc. of PODS, Montreal, Canada, 1996.

....University. 1 Introduction The notion of materialized view is essential in databases [Ull88] and is attracting more and more attention with the popularity of data warehouses [LZW 97] The problem of answering queries using materialized views [LMSS95, CKPS95, DG97a, BLR97, YL87, RSU95, LRU96, Ull97, DL97, Dus97, DG97b, LRO96] has been studied intensively. We propose a systematic study of its complexity. We also briefly consider the related problems of view consistency and view self maintainability [Huy97] Our results exhibit strong connections with two among the most studied ....

A. Y. Levy, A. Rajaraman, J. D. Ullman. Answering queries using limited external processors. In PODS-96.

....by the available views. By contrast, our algorithms check only sufficient conditions and might miss a plan because of the heuristics used. Our algorithm can be viewed as a generalization of algorithms that decide the subsumption of a datalog query by a datalog program (i.e. the description) [12] proposed Datalog for the description 38 of supported queries. It also suggested an algorithm that essentially finds what we call maximal CSQs. Recently [25] discussed the expressive power of Datalog and the expressive power of an RQDL extension. The most important result was that Datalog cannot ....

A. Levy, A. Rajaraman, and J. Ullman. Answering queries using limited external processors. In Proc. PODS, pages 227--37, 1996.

....query w sent to a wrapper by P there is a corresponding query w 0 of P 0 such that the sets of relations and conditions of w 0 are a superset of the corresponding sets of w and the set of exported attributes of w is a superset of the set of exported attributes of w 0 . Several projects [22, 16, 25, 21, 20, 27] propose and discuss query processors that, given some description of the capabilities of the participating sources, adapt to the different, limited capabilities of the sources. An elegant approach to describing capabilities was introduced in [22] where the supported query interfaces were ....

A. Levy, A. Rajaraman, and J. Ullman. Answering queries using limited external processors. In Proceedings of the Fifteenth ACM Symposium on Principles of Database Systems (PODS'96), pages 227--237, June 1996.

....[14] and the inverse rules algorithm [15] The inverse rules algorithm works for recursive queries but generates even more candidate solutions, that need to be verified, than the bucket al..gorithm. Rewriting queries utliizing views with specified binding patterns is considered in [16] Levy et al. [17] illustrate how an infinite set of views can be used to answer queries. The complexity of answering queries using materialized views is discussed in [18] Finally, the problem of answering queries in description logics and its complexities has been addressed in [19] 20] 7 Conclusion In the ....

A. Y. Levy, A. Rajaraman, and J.D. Ullman. Answering queries using limited external processors. In Proc. of the 15th Symp. on Principles of Database Systems, pages 227--237, 1996.

....by the available views. By contrast, our algorithms check only sufficient conditions and might miss a plan because of the heuristics used. Our algorithm can be viewed as a generalization of algorithms that decide the subsumption of a datalog query by a datalog program (i.e. the description) [19] proposed Datalog for the description of supported queries. It also suggested an algorithm that essentially finds what we call maximal CSQs. Recently [20] discussed the expressive power of Datalog and the expressive power of an RQDL extension. The most important result was that Datalog cannot ....

A. Levy, A. Rajaraman, and J. Ullman. Answering queries using limited external processors. In Proc. PODS, pages 227--37, 1996.

....algorithms also attempt to find view redefinitions that meet view preservation constraints specified by the view user, such as constraints imposed on the view extent or the view interface type. Unlike the strategies proposed for query rewriting using views in the database literature ( LRU96, SDJL96] our proposed techniques address three new issues: 1) finding view rewritings that are not necessarily equivalent to the original view definition as long as they meet user requirements 1 , 2) using semantic containment information for replacing the deleted information; and (3) ....

A. Y. Levy, A. Rajaraman, and J. D. Ullman. Answering queries using limited external processors. In Proceedings of the Fifteenth ACM SIGACT-SIGMOD-SIGART Symposium on Principles of Database Systems, pages 227--237, Montreal, Canada, 3--5 June 1996.

....available views. By contrast, our algorithms check only sufficient conditions and might miss a plan because of the heuristics used. Our algorithm can be viewed as a generalization of algorithms that decide the subsumption of a datalog query by a datalog program (i.e. the description) Recently [18] proposed Datalog for the description of supported queries. It also suggested an algorithm that essentially finds what we call maximal CSQs. 9 Conclusions and Future Work In this paper, we presented the Relational Query Description Language, RQDL, which provides powerful features for the ....

A. Levy, A. Rajaraman, and J. Ullman. Answering queries using limited external processors. In Proc. PODS, pages 227--37, 1996.

....parallels the concept of precision and recall from information retrieval [RJB89] though we now apply these concepts to the relational database context by addressing for example extent subset estimation. Much research has been done on query reformulation using materialized views. Levy et al. LRU96, LMS95, SDJL96] consider the problem of replacing an original query with a new expression containing materialized view definitions such that the new query is equivalent to the old one. To the best of our knowledge, generating queries without equivalence has not been studied in this context. 7 ....

A. Y. Levy, A. Rajaraman, and J. D. Ullman. Answering queries using limited external processors. In Proceedings of the Fifteenth ACM SIGACT-SIGMOD-SIGART Symposium on Principles of Database Systems, pages 227--237, Montreal, Canada, 3--5 June 1996.

....R.A= X where R resides at source S, declares that S can answer queries that pick all attributes of R and have R.A be bound to a constant. Then a query over the source data has to be rewritten to use correctly the contents and capabilities of the sources, i.e. to correctly use the available views [47, 30, 55, 24, 43, 14]. Indeed, in that case the query has to access only views and hence we need a total rewriting query. The above points highlight the importance of rewriting algorithms in relational databases and mediators. We believe that rewriting algorithms will be equally important for semistructured databases ....

....its additional restructuring power, MSL (as well as StruQL, which has the same restructuring capabilities) is not closed under query composition. This significantly reduces the applicability of the rewriting algorithm. The problem of query rewriting for conjunctive relational views is discussed in [28, 45, 30, 54, 55, 15, 14] and for recursive queries (but not recursive views) in [14] It is also related to the problems of query containment and query equivalence [10, 12] To the best of our knowledge, there is no work on the problem of rewriting semistructured queries using views. The only relevant work we are aware ....

A. Levy, A. Rajaraman, and J. Ullman. Answering queries using limited external processors. In Proc. PODS, pages 227--37, 1996.

.... a description of the wrappers capabilities, how can we answer a client query using only queries answerable (i.e. supported) by the wrappers We refer to this problem as the Capabilities Based Rewriting (CBR) problem [4, 5] it is also clearly related to the Answering Queries Using Views problem [6, 7, 8] (see Section 3) In this paper, we focus on sources that support conjunctive queries, i.e. their capabilities are a subset of CQ [9] The contributions of this paper are as follows: 1 In many cases the data reside at multiple sources and the mediator may have to locate them first. However, ....

....(ii) decide whether a query can be answered by combining supported queries (the CBR problem) This algorithm is run by the mediator. Our algorithm runs in time non deterministic exponential in the size of the query and the description, a substantial improvement over the algorithm described in [8], which was non deterministic doubly exponential. ffl We study the expressive power of p Datalog. We reach the important result that p Datalog can not describe the query capabilities of certain powerful sources. In particular, we show that there is no pDatalog program that can describe all ....

[Article contains additional citation context not shown here]

A. Levy, A. Rajaraman, and J.D. Ullman. Answering queries using limited external processors. In Proc. PODS Conf, pages 227--37, 1996.

....the set s 1 ; s k . Also, we assume no knowledge about the semantics of data stored at these sites, or about their query capabilities: in reality some sites may offer only restricted access, e.g. using a keyword search. For the case of conjunctive queries over relational databases, [LMSS96, LRU96] discuss techniques which can efficiently select the relevant sites and also use the limited query capabilities of such sites. 2 An Example We illustrate the problems, and the techniques we propose to solve them, for the query in Example 1.1. It is easier to describe first the view maintenance ....

Alon Levy, Anand Rajaraman, and Jeffrey Ullman. Answering queries using limited external processors. In PODS, 1996. To appear.

....much as possible of the processing to the source, thereby hopefully reducing the amount of local processing and the amount of data transmitted over the network. The problem of describing the computing capabilities of data sources and exploiting them to create query execution plans is considered in [56,82,96,114,119]. Query optimization. After the minimal set of data sources has been selected for a given query, a key problem is to find the optimal query execution plan for the query. The query execution plan specifies the order and scheduling in which the sources are accessed and the particular algorithms ....

A.Y. Levy, A. Rajaraman, J.D. Ullman, Answering queries using limited external processors, in: Proc. ACM SIGACT-SIGMOD-SIGART Symposium on Principles of Database Systems (PODS), Montreal, Quebec, 1996.

....do not involve regular path expressions with recursion. For the most part, considering queries with restructuring remains an open research problem. In nite number of views: Two works have considered the problem of answering queries using views in the presence of an in nite number of views [LRU96, VP97] The motivation for this seemingly curious problem is that when a data source has the capability to perform local processing, it can be modeled by the (possibly in nite) set of views it can supply, rather than a single one. Hence, to answer queries using such sources, one need not only ....

....local processing, it can be modeled by the (possibly in nite) set of views it can supply, rather than a single one. Hence, to answer queries using such sources, one need not only choose which sources to query, but also which query to send to it out of the set of possible queries it can answer. In [LRU96, VP97] it is shown that in certain important cases the problem of answering a query using an in nite set of 33 views is decidable. Of particular note is the case in which the set of views that a source can answer is described by the nite unfoldings of a datalog program. Description Logics: ....

Alon Y. Levy, Anand Rajaraman, and Jerey D. Ullman. Answering queries using limited external processors. In Proc. of the ACM SIGACT-SIGMOD-SIGART Symposium on Principles of Database Systems (PODS), Montreal, Canada, 1996.

....and of the query. 24 The results of [LMSS95] can also be extended to conjunctive queries with comparison predicates. The basic observation underlying this extension is that one only needs to consider rewritings that mention constants that are used in either the views or the query [Klu88, LRU96] In [RSU95] the authors extend the bound on the size of the rewriting to the case where the views contain binding pattern limitations (discussed in detail in Section 8.3) In [CR97] the authors exploit the close connection between the containment and rewriting problems, and show several ....

....consider the rewriting problem in the case where the query can create answer trees, and queries do not involve regular path expressions with recursion. Infinite number of views: Two works have considered the problem of answering queries using views in the presence of an infinite number of views [LRU96, VP97] The motivation is that when a data source has the capability to perform local processing, it can be modeled by a (possibly infinite) set of views it can supply, rather than a single one. Hence, to answer queries using such sources, one need not only choose which sources to query, but also ....

[Article contains additional citation context not shown here]

Alon Y. Levy, Anand Rajaraman, and Je#rey D. Ullman. Answering queries using limited external processors. In Proc. of the ACM SIGACT-SIGMODSIGART Symposium on Principles of Database Systems (PODS), Montreal, Canada, 1996.

No context found.

Levy, A. Y., Rajaraman, A., and Ullman, J. D. (1996c). Answering queries using limited external processors. In Proc. of the ACM SIGACTSIGMOD -SIGART Symposium on Principles of Database Systems (PODS), Montreal, Canada.

....much as possible of the processing to the source, thereby hopefully reducing the amount of local processing and the amount of data transmitted over the network. The problem of describing the computing capabilities of data sources and exploiting them to create query execution plans is considered in [97, 115, 83, 57, 120] Query optimization: After the minimal set of data sources has been selected for a given query, a key problem is to nd the optimal query execution plan for the query. The query execution plan speci es the order and scheduling in which the sources are accessed and the particular algorithms used ....

Alon Y. Levy, Anand Rajaraman, and Jerey D. Ullman. Answering queries using limited external processors. In Proc. of the ACM SIGACT-SIGMOD-SIGART Symposium on Principles of Database Systems (PODS), Montreal, Canada, 1996.

....equivalent plan is presented. Later, Kwok and Weld [20] showed that if we restrict our plans to be sets of conjunctive queries, then there may not be a finite maximallycontained rewriting in the presence of binding pattern limitations. More complex query capabilities in sources are considered in [24]. Complex capabilities are modeled by the ability of a source to answer a potentially infinite number of conjunctive queries. Hence, 24] considered how to answer queries given an infinite number of conjunctive source descriptions. Several authors have considered the problem of rewriting queries ....

....may not be a finite maximallycontained rewriting in the presence of binding pattern limitations. More complex query capabilities in sources are considered in [24] Complex capabilities are modeled by the ability of a source to answer a potentially infinite number of conjunctive queries. Hence, [24] considered how to answer queries given an infinite number of conjunctive source descriptions. Several authors have considered the problem of rewriting queries using views for query optimization [32,6,30] In this context, one usually requires a query plan that is equivalent to the original query. ....

A. Y. Levy, A. Rajaraman, and J. D. Ullman. Answering queries using limited external processors. In Proceedings of the 15th ACM SIGACT-SIGMODSIGART Symposium on Principles of Database Systems, Montreal, Canada, 1996.

....to it. The Information Manifold incorporated several algorithms for adapting to differing source capabilities. When possible, the system would attempt to use as much as possible the query processing capabilities of its data sources, in order to reduce the amount of processing done locally [LRO96b, LRU96] 4 What we did as a community In the past few years, significant progress was made by each of the groups working on data integration (e.g. GMPQ 97, EW94, FW97, DG97, AKS96, Coh98, ACPS96, HZ96, FRV96, HKWY97] However, we have also made progress as a community. In particular, we have ....

Alon Y. Levy, Anand Rajaraman, and Jeffrey D. Ullman. Answering queries using limited external processors. In Proc. of the ACM SIGACT-SIGMOD-SIGART Symposium on Principles of Database Systems (PODS), Montreal, Canada, 1996.

No context found.

Alon Y. Levy, Anand Rajaraman, and Jeffrey D. Ullman. Answering queries using limited external processors. In Proceedings of the 15th ACM SIGACT-SIGMOD-SIGART Symposium on Principles of Database Systems, Montreal, Canada, 1996.

No context found.

Alon Y. Levy, Anand Rajaraman, and Jerey D. Ullman. Answering queries using limited external processors. In Proc. of PODS, pages 227-237, Montreal, Canada, 1996.

No context found.

A. Y. Levy, A. Rajaraman, and J. D. Ullman. Answering queries using limited external processors. In Proc. of PODS, pages 227--237, Montreal, Canada, 1996.

No context found.

A. Y. Levy, A. Rajaraman, and J. D. Ullman. Answering Queries Using Limited External Processors. In Proceedings of PODS, 1996.

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