S. Chaudhuri and M. Vardi. Optimizing real conjunctive queries. In Proc. of PODS, 1993.  Home/Search   Document Not in Database   Summary   Related Articles   Check

....Under bag semantics, the ways in which views may be combined to answer a query are more limited. This is due to the fact that two queries are equivalent if and only if there is a bi directional 1 1 mapping between the two queries, which maps the join predicates of one query to those of the other [CV93] Hence, if we ignore the arithmetic comparison operators, a view is usable only if it is isomorphic to a subset of the query. An additional di erence between [TSI96] and [CKPS95] is that the latter searches the space of join orderings in a top down 15 Conventional optimizer Optimizer using ....

....query removes duplicates in the select clause, the view cannot be used to answer a query. Another important point to recall about this context is that because of the bag semantics a view will be usable to answer a query only if there is an isomorphism between the view and a subset of the query [CV93] The work described in [ZCL 00] extends the treatment of grouping and aggregation to consider multi block queries and to multi dimensional aggregation functions such as cube, rollup and grouping sets [GBLP98] Several works [CNS99, GRT99, GT00] consider the formal aspects of answering ....

Surajit Chaudhuri and Moshe Vardi. Optimizing real conjunctive queries. In Proc. of the ACM SIGACT-SIGMOD-SIGART Symposium on Principles of Database Systems (PODS), pages 59-70, Washington D.C., 1993.

....be a topic of a specialized survey. Some of the cases which are most relevant to our discussion include: containment of conjunctive queries and unions thereof [CM77, SY81] conjunctive queries with built in comparison predicates [Klu88, LS93, ZO93, KMT98] and datalog queries [Shm93, Sag88, LS93, CV93, CV94] 3.3 Rewriting of a Query Using Views Given a query Q and a set of view definitions V 1 , Vm , a rewriting of the query using the views is a query expression Q # that refers only to the views V 1 , Vm . In SQL, a query refers 10 only to the views if all the relations ....

....with multiset semantics which may also include arithmetic comparison operators. Under multiset semantics, the ways in which views may be combined to answer a query are more limited. This is due to the fact that two queries are equivalent if and only if there is a 1 1 isomorphism between them [CV93] Hence, if we ignore the arithmetic comparison operators, a view is usable only if it is isomorphic to a subset of the query. As a result, the join enumeration algorithms become slightly simpler than the one discussed above. Both [TSI96] and [CKPS95] present experimental results that show that ....

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Surajit Chaudhuri and Moshe Vardi. Optimizing real conjunctive queries. In Proc. of the ACM SIGACT-SIGMOD-SIGART Symposium on Principles of Database Systems (PODS), pages 59--70, Washington D.C., 1993.

....than once; also, a view can concern elements from any document (when the URI of the document is not speci ed) 7.2 Rewriting algorithm Although abundant work on query rewriting using views for set semantics exists, there are quite few results in the case of bag semantics. The result stated in [5] is that two conjunctive SQL queries are equivalent only if they are identical up to renaming and reordering of tables; this problem can be brought to the problem of deciding graph isomorphism, and is in NP . This forms the basis of our algorithm; we rst explain all the necessary enhancements by ....

....of tables; this problem can be brought to the problem of deciding graph isomorphism, and is in NP . This forms the basis of our algorithm; we rst explain all the necessary enhancements by the mean of an example, on a simple unnested SQL query. Basic algorithm A simple algorithm resulting from [5] is the following. Given the SQL unnested, non recursive 2 query Q and views V 1 ; Vn , nd all subsets fV i1 ; V i2 ; V ik g of V 1 ; Vn such that Q is isomorphic to a query over V i1 . V ik (note that these subsets may contain repetitions) 2 We do not ....

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Surajit Chaudhuri and Moshe Vardi. Optimizing real conjunctive queries. In Proc. of the Symposium on Principles of Database Systems (PODS), pages 5970, Washington D.C., 1993.

.... which are most relevant to our discussion include: containment of conjunctive queries and unions thereof Chandra and Merlin, 1977; Sagiv and Yannakakis, 1981, conjunctive queries with built in comparison predicates Klug, 1988, and datalog queries Shmueli, 1993; Sagiv, 1988; Levy and Sagiv, 1993; Chaudhuri and Vardi, 1993; Chaudhuri and Vardi, 1994. 3. CHALLENGES IN DATA INTEGRATION As described in the introduction, the task of a data integration system is to provide a uniform interface to a collection of data sources. The data sources can either be full edged database systems (of various avors: 4 relational, ....

.... many real world domains, we need to develop reasoning techniques (extensions of query containment algorithms and algorithms for answering queries using views) to settings where the queries involve bags, grouping and aggregation, and nested structures (see Cohen et al. 1999; Levy and Suciu, 1997; Chaudhuri and Vardi, 1993; Srivastava et al. 1996 for some work in these areas) Another interesting question is whether some of these features can be incorporated into knowledge representation languages. Notes 1. However, if we also knew that the course name functionally determines its number, then we could prune V4 ....

Chaudhuri, S. and Vardi, M. (1993). Optimizing real conjunctive queries. In Proc. of the ACM SIGACT-SIGMOD-SIGART Symposium on Principles of Database Systems (PODS), pages 59-70, Washington D.C.

.... work on containment has considered queries in the relational algebra [CM77, SY81, ASU79] and datalog [Shm93, Sag88, CV92] Several works have considered the extension of containment algorithms for queries involving order [Klu88, vdM92, LS93, ZO93, GSUW94] Queries over bags were considered in [CV93], and modifications of containment algorithms to consider semantics of class hierarchies were considered in [Cha92, LR96] However, containment and equivalence for query languages for complex objects have not been considered previously. Complex Objects Several query formalisms have been proposed ....

Surajit Chaudhuri and Moshe Vardi. Optimizing real conjunctive queries. In The Proceedings of the Twelfth ACM SIGACT-SIGMOD-SIGART Symposium on Principles of Database Systems, Washington D.C., pages 59--70, 1993.

....work we plan to characterize those nontrivial classes of queries and deductive rules for which our method always terminates. Other possible extensions of our work would be to consider QC in the presence of aggregate functions, queries over bags, or in object oriented databases as addressed in [LS97, CV93, BH97, BJNS94], to mention some previous work. 20 ....

S. Chaudhuri, M. Vardi: "Optimizing real conjunctive queries". Proceedings of the PoDS'93. ACM Press, 1993, pp. 59-70.

....meaningfulness of the containment checking tests and extend our framework to the field of constraint databases. Other possible extensions of our work would be to consider query containment in the presence of aggregate functions, queries over bags, or in object oriented databases as addressed in [LS97, CV93, BH97, BJNS94], to mention some previous work. Acknowledgements This work has been partially supported by PRONTIC CICYT program project TIC97 1157. ....

S. Chaudhuri, M. Vardi: "Optimizing real conjunctive queries". Proceedings of the 14 th ACM SIGACT-SIGMOD-SIGART Symposium on Principles of Database Systems (PoDS'93). ACM Press, 1993, pp. 59-70.

.... constraints [23] Previous work on query containment has considered queries in the relational algebra [11, 36, 3] and datalog [38, 37, 14] Several works have considered the extension of containment algorithms for queries involving order [26, 42, 31, 44, 23] Queries over bags were considered in [15], and modifications of containment algorithms to consider semantics of class hierarchies were considered in [10, 30] However, containment and equivalence for query languages for complex objects have not been considered previously. Complex Objects Several query formalisms have been proposed [40, ....

Surajit Chaudhuri and Moshe Vardi. Optimizing real conjunctive queries. In ACM PODS, 1993.

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S. Chaudhuri and M. Vardi. Optimizing real conjunctive queries. In Proc. of PODS, 1993.

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S. Chaudhuri and M. Vardi. Optimizing real conjunctive queries. In Proc. of PODS, 1993.

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Surajit Chaudhuri and Moshe Vardi. Optimizing real conjunctive queries. In Proc. of PODS, pages 59-70, Washington D.C., 1993.

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S. Chaudhuri and M. Vardi. Optimizing real conjunctive queries. In Proc. of PODS, pages 59--70, Washington D.C., 1993.

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