LARSON, P.-A. AND YANG, H. Z. 1985. Computing queries from derived relations. In Proceedings of the 11th VLDB Conference (Stockholm, Sweden), pp. 259--269.  Home/Search   Document Not in Database   Summary   Related Articles   Check

.... in query folding: the first comes from the number of possible mappings from the resources to the query, and the second is to determine which parts of the query can be removed when the mapped resources are added to the query( LMS95] A lot of research work has been done in query folding([LY85], YL87] CKPS95] LMS95] Qia96] Gry98] etc. In the earlier work of Yang and Larson [LY85] they gave necessary and sufficient conditions for when a query is computable from a single derived relation; in [YL87] they considered the problem of finding rewritings for conjunctive queries ....

....to the query, and the second is to determine which parts of the query can be removed when the mapped resources are added to the query( LMS95] A lot of research work has been done in query folding( LY85] YL87] CKPS95] LMS95] Qia96] Gry98] etc. In the earlier work of Yang and Larson [LY85], they gave necessary and sufficient conditions for when a query is computable from a single derived relation; in [YL87] they considered the problem of finding rewritings for conjunctive queries using the available set of derived relations. Their approach considers what amounts to one to one ....

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P.A.Larson and H.Z.Yang, Computing Queries from Derived Relations, In Proceedings of VLDB conference, 1985

....speeding up subsequent query processing has been studied widely in previous literature. The benefit of this technique is obtained from saving (part of) the subsequent query computations by utilizing the previous cached (intermediate) results. Applications of this technique can be found in [Fin82, LY85, DR92, Sel87, Rou91, Jhi88, HS93, AL80] In [Fin82, LY85, Rou91] cached query results were used in relational database systems to avoid repeated computations. Sel87, Jhi88] addressed the problem This research was sponsored partially by NSF under grant IRI 9057573 and GDR 85 00108 and by ....

....widely in previous literature. The benefit of this technique is obtained from saving (part of) the subsequent query computations by utilizing the previous cached (intermediate) results. Applications of this technique can be found in [Fin82, LY85, DR92, Sel87, Rou91, Jhi88, HS93, AL80] In [Fin82, LY85, Rou91] cached query results were used in relational database systems to avoid repeated computations. Sel87, Jhi88] addressed the problem This research was sponsored partially by NSF under grant IRI 9057573 and GDR 85 00108 and by NASA USRA under contract FCPO 550 81. This paper also appears in ....

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P.- A. Larson and H. Z. Yang. Computing queries from derived relations. In Procs. of 11th VLDB, pages 259--269, 1985.

....we obtain are union queries. Our attention is focused on how to quickly find rewritings that give as many correct answers as possible, rather than on how e#ciently the rewritings can be evaluated. 1. 1 Previous Work Apparently the first papers dealing with query rewriting using views are [3] and [4] in which equivalent rewritings of conjunctive queries are discussed. Over the past few years, the problem has received intensive attention mainly because of its relevance to data integration and query optimization. For a comprehensive survey, see [5] Here we only mention a few papers ....

P.-A. Larson and H. Z. Yang. Computing queries from derived relations. In Proc. of VLDB, pages 259--269, 1985.

....evaluation in batch of a set of queries. The developed techniques are geared towards finding and reusing common sub expressions in the set of queries and are heuristics based. The idea of the caching of query results to optimize the processing of subsequent queries was first studied in [11] and [17]. The developed techniques are restricted to a subset of extensional, conjunctive queries. No self joins are permitted. The techniques do not, however, find queries that are contained by the original query. In [8] the ADMS system is described, which includes a query caching system based on ....

P.-A. Larson and H. Yang. Computing queries from derived relations. In Proc. of 11th VLDB, pages 259--269, 1985.

....views have a rather restricted form that makes the problem somehow easier. Query processing in DynaMat, described in section 4.1 implements a simple rewriting policy based on a multi dimensional description of the stored results. In the general case of SPJ views, there are quite a few algorithms [Larson and Yang 1985; Yang and Larson 1987; Chaudhuri et al. 1995; Levy et al. 1995; Srivastava et al. 1996] that could be used to optimize the execution of user queries against the fragments. Even though such techniques are applicable for our case, we chose a cleaner engineering oriented approach that in practice ....

Larson, P.-A. and Yang, H. Z. 1985. Computing Queries from Derived Relations. In Proceedings of the 11th VLDB Conference (Stockholm, Sweden, 1985), pp. 259--269.

....50smngr(name) Both evaluations yield identical results. However, when the emp relation is stored remotely or temporarily unavailable due to network partition, using the evaluation E2 against the stored queries is much more efficient. 2 Semantic caching (Dar et al. 1996; Keller and Basu, 1996; Larson and Yang, 1985; Ren and Dunham, 1998; Sellis, 1988) exploits the semantic locality of the queries by caching a set of semantically associated results, instead of tuples or pages which are used in conventional caching. Semantic caching can be particularly effective in improving performance when a series of ....

....(Saraiya, 1991; Ullman, 1997) 2.2. Related Work Past research areas related to semantic caching include conventional caching (Alonso et al. 1990; Franklin et al. 1993) query satisfiability and containment problems (Guo et al. 1996; Ullman, 1988) view materialization (Levy et al. 1995; Larson and Yang, 1985), query folding (Qian, 1996) and semantic query optimization (Chu et al. 1994) Recently, semantic caching in a client server or multi database architecture has received attention (Ashish et al. 1998; Dar et al. 1996; Godfrey and Gryz, 1999; Keller and Basu, 1996; Ren and Dunham, 1998; ....

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Larson, P.- A. and H. Z. Yang. Computing Queries from Derived Relations. Proc. VLDB , 1985.

....view, we need only look up the Price and Finance attribute from Dealer3 using the value of CarID for each tuple in the current answer set. This is likely to be much cheaper than computing a three way join from scratch. 2 1.2. Related Work Previous work on using views to answer queries includes [LY85, YL87, SJGP90, TSI94, CR94, CKPS95, LMSS95, RSU95] Subsequently, GHQ95, SDJY96] discuss how to answer aggregate queries using materialized aggregate views. TSI94, CKPS95] also describe how to incorporate their techniques in a traditional cost based query optimizer. The problem of view ....

P. A. Larson and H.Z. Yang. Computing queries from derived relations. In VLDB , pages 259--269, 1985.

....(A; B) and S = B; C) and one view V = R . S, and consider the query Q = oe A=a R. Clearly, Q cannot be answered from the view V , because the join would not necessarily include all of R s tuples. This translation problem (for conjunctive queries and views) has been addressed by Larson and Yang [10, 11], by Levy et al. 12] and by Brodsky and Motro [5] We shall assume that a translation algorithm exists which is sound and complete; i.e. it computes all the correct translations that exist. 7 Assume a multidatabase with scheme D and mapped views M . The answer to a query Q on this ....

P.-A. Larson and H. Z. Yang. Computing queries from derived relations. In Proceedings of the Eleventh International Conference on Very Large Data Bases (Stockholm, Sweden, August 21--23), pages 259--269, 1985.

....the desired result. The simpler queries are passed simultaneously to the DBMS for processing. Optimizing such interdependent queries separately leads to performance that is far from optimal. This has led to several approaches to exploit the dependencies between queries such as illustrated by [AlRa94, Jark84, Kim84, LaYa85, Rous82a, Rous82b, Sell88]. In [Jark84] the author describes how common subexpressions can be detected, and used according to their type (e.g. joins, selections, etc. In [LaYa85] necessary and sufficient conditions are discussed to compute query results from previously executed queries. In [Rous82a, Rous82b] a ....

....to several approaches to exploit the dependencies between queries such as illustrated by [AlRa94, Jark84, Kim84, LaYa85, Rous82a, Rous82b, Sell88] In [Jark84] the author describes how common subexpressions can be detected, and used according to their type (e.g. joins, selections, etc. In [LaYa85], necessary and sufficient conditions are discussed to compute query results from previously executed queries. In [Rous82a, Rous82b] a framework is provided to derive a common query graph from individual query graphs belonging to individual views, in an attempt to speed up view processing. In the ....

Larson, P-A., Yang, H.Z., Computing Queries from Derived Relations, in Proc. 11th Int. Conf. on Very Large Data Bases, pp. 259-269.

....on a given set of views of these relations has been encountered in at least three applications. In this section we describe these applications and we comment on the solutions that have been designed. 2. 1 Physical Database Design The first to have addressed this problem have been Larson and Yang [4, 5]. The context in which the problem was discussed is physical database design for relational databases. The standard approach to physical database design is to maintain a one to one correspondence between the relations declared in the scheme of the database and the relations that are actually ....

P.-A. Larson and H. Z. Yang. Computing queries from derived relations. In Proceedings of the Eleventh International Conference on Very Large Data Bases (Stockholm, Sweden, August 21--23), pages 259--269. Morgan Kaufmann, Los Altos, California, 1985.

....that occur in Q s predicate for further qualifying the result, or some of Q s attributes are not contained in P. Hence, to solve the computable problem, not only the predicate relationship but also the relationship between attributes must be examined. The related computable work can be found in [LY85] and [CKS99] Processing queries via a semantic cache is examined in [DFJ96] CR94] and [KB96] DFJ96] works on only select queries, it treats all the candidate semantic regions as a whole to compute the corresponding probe 5 and remainder queries. CR94] works in a centralized system model ....

....operations, with F 1 involving only attributes in SA , such that F 1 (SC ) 6= and F 1 (SC ) F 2 (QC ) Furthermore, if F 1 (SC ) QC , we say Q is fully answered from S; otherwise, we say Q is partially answered from S. De nition 8 is derived from the concept of Derivability de ned in [LY85]. From De nition 8, we know that the key issue to compute a query from a cached segment is to nd the corresponding functions F 1 and F 2 , and to make sure that F 1 can be executed on the segment. Sometimes, even the entire result of a query Q is contained in a segment S, Q still is not ....

P.A.Larson and H.Z.Yang, Computing Queries from Derived Relations, Proceedings of VLDB conference, 1985, pp. 259-269

....optimal CSQs from the given descriptions. Also, we provide algorithms for generating plans for Q by combining the results of these CSQs using selections, projections, and joins. The CBR problem is related to the problem of determining how to answer a query using a set of materialized views [13, 9, 18, 17]. However, there are significant differences. These papers consider a specification language that uses SPJ expressions over given relations specifying a finite number of views. They cannot express arbitrary relations, arbitrary arities, binding requirements (with the exception of [18] or ....

P.A. Larson and H.Z. Yang. Computing queries from derived relations. In Proc. VLDB Conf., pages 259--69, 1985.

....in the presence of materialized cached views, as a subroutine. By virtue of working on a general DAG structure, our techniques are extensible, unlike the solutions of [CKPS95] and [CR94] The problem of detecting whether an expression can be used to compute another has also been studied in [LY85, YL87, Sel88a] however, they do not address the problem of choosing what to materialize, or the problem of finding the best query plans in a cost based fashion. Our algorithms have been described in the context of a Volcano like optimizer; at least two commercial database systems, from ....

P. A. Larson and H. Z. Yang. Computing queries from derived relations. In Intl. Conf. Very Large Databases, pages 259--269, Stockholm, 1985.

....by classifying the concepts in a concept hierarchy, and then computing them starting with the parent concepts. This corresponds to evaluating a new Classic query (the new concept) using information in several materialized views (the old concepts) Classic has been used for data archaeology. LY85, YL87] look at the question of answering queries using cached results or materialized views. LY85, YL87] show how to transform an SPJ (select project join) query so that it is expressed completely using a given set of views, without any reference to the base relations. They also have the idea of ....

....parent concepts. This corresponds to evaluating a new Classic query (the new concept) using information in several materialized views (the old concepts) Classic has been used for data archaeology. LY85, YL87] look at the question of answering queries using cached results or materialized views. LY85, YL87] show how to transform an SPJ (select project join) query so that it is expressed completely using a given set of views, without any reference to the base relations. They also have the idea of augmented views where each view is extended with keys of the underlying base relations. CKPS95] ....

P. A. Larson and H.Z. Yang. Computing queries from derived relations. In VLDB , pages 259--269, 1985.

....here: we are interested in generating and efficiently evaluating a query (view) from which an unfolding has been removed. Thus, the resulting query is not equivalent to the original query. The problem we address is also different from the problem of answering queries using materialized views [2, 14, 16, 20]. In the latter problem, the goal is to replace subqueries of a query by views (or other queries) to generate a query equivalent or contained in the original query. Our goal, again, is to remove, or more precisely to avoid evaluating, parts of a query for optimization or security reasons. The ....

P.-A. Larson and H. Yang. Computing queries from derived relations. In Proc. of 11th VLDB, pages 259--269, 1985.

....between the approaches has to be predetermined. Thus, the optimizer can not explore both the options depending on the query and cost estimations. The task of generating equivalent queries based on existing query fragments or semantic knowledge has been studied in several different contexts [Fin82, LY85, YL87, Sel88, CGM90, CS93, CR94] However, all these techniques generate equivalent queries explicitly . In contrast, much of our efficiency in optimization stems from the implicit encoding of the set of equivalent queries in MapTable and a join enumeration algorithm that exploits the encoding. ....

P. A. Larson and H. Z. Yang. Computing queries from derived relations. In Proceedings of the 11th International VLDB Conference, pages 259--269, Stockholm, August 1985.

....which enables us to use point predicates to describe semantic caching in detail, and (3) we provide detail analysis on various match types in semantic caching. Finding proper match types for the input query in the semantic cache is analogous to rewriting input query via materialized view [LY85, GM95, Qia96] or the query containment problem [Ull88, Cha92, LMSS95] The major focus of these works is to reduce the number of database relation literals in the rewritten query using materialized view relation literals. Therefore, caching was not their primary concern. Our work more focuses ....

P.-A. Larson and H. Z. Yang. "Computing Queries from Derived Relations". In Proc. of the 11th Int'l Conf. on Very Large Data Bases (VLDB), pages 259--269, Stockholm, Sweden, August 1985. 20

....is treated in Section 5. Section 6 contains concluding remarks and possible extensions. An extended version of this work appears on [29] 2 Related work The DW configuration problem relates to several overlapping research areas. Answering queries using materialized views has been studied in [14, 34, 30, 15, 4]. The same issue, in connection to aggregate queries and views, has been studied in [7] while in [5] multiset semantics is additionally considered. The problem of optimizing query evaluation in the presence of materialized views has been studied in [30, 4] The problem of maintaining ....

P.-A. Larson and H. Yang. Computing Queries from Derived Relations. In Proc. of VLDB, pages 259--269, 1985.

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LY85 Larson, P.-A. and Yang, H.Z., Computing Queries from Derived Relations. Proc. of 11th Intl. Conf. on Very Large Data Bases, (1985), 259-269.

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LARSON, P.-A. AND YANG, H. Z. 1985. Computing queries from derived relations. In Proceedings of the 11th VLDB Conference (Stockholm, Sweden), pp. 259--269.

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P.- A. Larson and H. Z. Yang. Computing queries from derived relations. In A. Pirotte and Y. Vassiliou, editors, VLDB'85, Proceedings of 11th International Conference on Very Large Data Bases, August 21-23, 1985.

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P.- A. Larson and H. Z. Yang. Computing queries from derived relations. In A. Pirotte and Y. Vassiliou, editors, VLDB'85, Proceedings of 11th International Conference on Very Large Data Bases, August 21-23, 1985.

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P A Larson and H Z Yang, " Computing Queries from Derived Relations" , Proc. VLDB , 1985.

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P. Larson, H. Z. Yang. Computing Queries from Derived Relations. In Proc. of VLDB 1985. Proceedings of the 11 th International Conference on Very Large Data Bases (VLDB), Stockholm, Sweden, Morgan Kaufmann Publishers, August 1985.

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Larson, P-A., Yang, H.Z., Computing Queries from Derived Relations, in Proc. 11th Int. Conf. on Very Large Data Bases, Morgan Kaufman, pp. 259-269, 1985.

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