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79
Answering queries using views
- In PODS Conference
, 1995
"... We consider the problem of computing answers to queries by using materialized views. Aside from its potential in optimizing query evaluation, the problem also arises in applications such as Global Information Systems, Mobile Computing and maintaining physical data independence. We consider the probl ..."
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Cited by 447 (32 self)
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We consider the problem of computing answers to queries by using materialized views. Aside from its potential in optimizing query evaluation, the problem also arises in applications such as Global Information Systems, Mobile Computing and maintaining physical data independence. We consider the problem of nding a rewriting of a query that uses the materialized views, the problem of nding minimal rewritings, and nding complete rewritings (i.e., rewritings that use only the views). We show that all the possible rewritings can be obtained by considering containment mappings from the views to the query, and that the problems we consider are NP-complete when both the query and the views are conjunctive and don't involve built-in comparison predicates. We show that the problem has two independent sources of complexity (the number of possible containment mappings, and the complexity of deciding which literals from the original query can be deleted). We describe a polynomial time algorithm for nding rewritings, and show that under certain conditions, it will nd the minimal rewriting. Finally, we analyze the complexity of the problems when the queries and views may be disjunctive and involve built-in comparison predicates. 1
Maintenance of Materialized Views: Problems, Techniques, and Applications
, 1995
"... In this paper we motivate and describe materialized views, their applications, and the problems and techniques for their maintenance. We present a taxonomy of view maintenanceproblems basedupon the class of views considered, upon the resources used to maintain the view, upon the types of modi#cati ..."
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Cited by 314 (9 self)
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In this paper we motivate and describe materialized views, their applications, and the problems and techniques for their maintenance. We present a taxonomy of view maintenanceproblems basedupon the class of views considered, upon the resources used to maintain the view, upon the types of modi#cations to the base data that areconsidered during maintenance, and whether the technique works for all instances of databases and modi#cations. We describe some of the view maintenancetechniques proposed in the literature in terms of our taxonomy. Finally, we consider new and promising application domains that are likely to drive work in materialized views and view maintenance. 1 Introduction What is a view? A view is a derived relation de#ned in terms of base #stored# relations. A view thus de#nes a function from a set of base tables to a derived table; this function is typically recomputed every time the view is referenced. What is a materialized view? A view can be materialized by storin...
Materialized view maintenance and integrity constraint checking: Trading space for time
, 1996
"... Abstract We investigate the problem of incremental maintenance of an SQL view in the face of database updates, and show that it is possible to reduce the total time cost of view maintenance by materializing (and maintaining) additional views. We formulate the problem of determining the optimal set o ..."
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Cited by 115 (7 self)
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Abstract We investigate the problem of incremental maintenance of an SQL view in the face of database updates, and show that it is possible to reduce the total time cost of view maintenance by materializing (and maintaining) additional views. We formulate the problem of determining the optimal set of additional views to materialize as an optimization problem over the space of possible view sets (which includes the empty set). The optimization problem is harder than query optimization since it has to deal with multiple view sets, updates of multiple relations, and multiple ways of maintaining each view set for each updated relation. We develop a memoing solution for the problem; the solution can be implemented using the expression DAG representation used in rule-based optimizers such as Volcano. We demonstrate that global optimization cannot, in general, be achieved by locally optimizing each materialized subview, because common subexpressions between different materialized subviews can allow nonoptimal local plans to be combined into an optimal global plan. We identify conditions on materialized subviews in the expression DAG when local optimization is possible. Finally, we provide a systematic space of heuristics that can be used to efficiently determine a useful set of additional views to materialize. Our results are particularly important for the efficient checking of assertions (complex integrity constraints) in the SQL-92 standard, since the incremental checking of such integrity constraints is known to be essentially equivalent to the view maintenance problem.
Practical Lineage Tracing in Data Warehouses
- In ICDE
, 1999
"... We consider the view data lineage problem in a warehousing environment: For a given data item in a materialized warehouse view, we want to identify the set of source data items that produced the view item. We formalize the problem and present a lineage tracing algorithm for relational views with agg ..."
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Cited by 102 (8 self)
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We consider the view data lineage problem in a warehousing environment: For a given data item in a materialized warehouse view, we want to identify the set of source data items that produced the view item. We formalize the problem and present a lineage tracing algorithm for relational views with aggregation. Based on our tracing algorithm, we propose a number of schemes for storing auxiliary views that enable consistent and efficient lineage tracing in a multisource data warehouse. We report on a performance study of the various schemes, identifying which schemes perform best in which settings. Based on our results, we have implemented a lineage tracing package in the WHIPS data warehousing system prototype at Stanford. With this package, users can select view tuples of interest, then efficiently "drill down" to examine the source data that produced them. 1 Introduction Data warehousing systems collect data from multiple distributed sources, integrate the information as materialized v...
Answering Queries with Aggregation Using Views
, 1996
"... We present novel algorithms for the problem of using materialized views to compute answers to SQL queries with grouping and aggregation, in the presence of multiset tables. In addition to its obvious potential in query optimization, this problem is important in many applications, such as data wareho ..."
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Cited by 86 (3 self)
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We present novel algorithms for the problem of using materialized views to compute answers to SQL queries with grouping and aggregation, in the presence of multiset tables. In addition to its obvious potential in query optimization, this problem is important in many applications, such as data warehousing, very large transaction recording systems, global information systems and mobile computing, where access to local or cached materialized views may be cheaper than access to the underlying database. Our contributions are the following: First, we show that in the case where the query has grouping and aggregation but the views do not, a view is usable in answering a query only if there is an isomorphism between the view and a portion of the query. Second, when the views also have grouping and aggregation we identify conditions under which the aggregation information present in a view is sufficient to perform the aggregation computations required in the query. The algorithms we describe fo...
Mapping Adaptation under Evolving Schemas
- IN VLDB
, 2003
"... To achieve interoperability, modern information systems and e-commerce applications use mappings to translate data from one representation to another. In dynamic environments like the Web, data sources may change not only their data but also their schemas, their semantics, and their query capab ..."
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Cited by 71 (8 self)
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To achieve interoperability, modern information systems and e-commerce applications use mappings to translate data from one representation to another. In dynamic environments like the Web, data sources may change not only their data but also their schemas, their semantics, and their query capabilities. Such changes must be reflected in the mappings. Mappings left inconsistent by a schema change have to be detected and updated. As large, complicated schemas become more prevalent, and as data is reused in more applications, manually maintaining mappings (even simple mappings like view definitions) is becoming impractical. We present a novel framework and a tool (ToMAS) for automatically adapting mappings as schemas evolve. Our approach considers not only local changes to a schema, but also changes that may affect and transform many components of a schema. We consider a comprehensive class of mappings for relational and XML schemas with choice types and (nested) constraints...
The CVS Algorithm for View Synchronization in Evolvable Large-Scale Information Systems
- In EDBT’98
, 1998
"... Abstract. Current view technology supports only static views in the sense that views become unde ned and hence obsolete as soon as the underlying information sources (ISs) undergo capability changes. We propose to address this new view evolution problem- which we call view synchronization-byanovel s ..."
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Cited by 30 (20 self)
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Abstract. Current view technology supports only static views in the sense that views become unde ned and hence obsolete as soon as the underlying information sources (ISs) undergo capability changes. We propose to address this new view evolution problem- which we call view synchronization-byanovel solution approach that allows a ected view de nitions to be dynamically evolved to keep them in synch with evolving ISs. We present in this paper a general strategy for the view synchronization process that guided by constraints imposed by the view evolution preferences embedded in the view de nition achieves view preservation (i.e., view rede nition). We present the formal correctness, the CVS algorithm, as well as numerous examples to demonstrate the main concepts. 1
Incementally Maintaining Materializations of Ontologies Stored in Logic Databases
- In Journal of Data Semantics II, LNCS, Vol 3360
, 2005
"... Abstract. This article presents a technique to incrementally maintain materializations of ontological entailments. Materialization consists in precomputing and storing a set of implicit entailments, such that frequent and/or crucial queries to the ontology can be solved more efficiently. The central ..."
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Cited by 29 (1 self)
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Abstract. This article presents a technique to incrementally maintain materializations of ontological entailments. Materialization consists in precomputing and storing a set of implicit entailments, such that frequent and/or crucial queries to the ontology can be solved more efficiently. The central problem that arises with materialization is its maintenance when axioms change, viz. the process of propagating changes in explicit axioms to the stored implicit entailments. When considering rule-enabled ontology languages that are operationalized in logic databases, we can distinguish two types of changes. Changes to the ontology will typically manifest themselves in changes to the rules of the logic program, whereas changes to facts will typically lead to changes in the extensions of logical predicates. The incremental maintenance of the latter type of changes has been studied extensively in the deductive database context and we apply the technique proposed in [31] for our purpose. The former type of changes has, however, not been tackled before. In this article we elaborate on our previous papers [34,35], which extend the approach of [31] to deal with changes in the logic program. Our approach is not limited to a particular ontology language but can be generally applied to arbitrary ontology languages that can be translated to Datalog programs, i.e. such as O-Telos, F-Logic [17] RDF(S), or Description Logic Programs [36]. 1
Answering Queries Using Limited External Query Processors
- In Proceedings of the 15th ACM SIGACT-SIGMOD-SIGART Symposium on Principles of Database Systems
, 1996
"... When answering queries using external information sources, their contents can be described by views. To answer a query, we must rewrite it using the set of views presented by the sources. When the external information sources also have the ability to answer some (perhaps limited) sets of queries tha ..."
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Cited by 29 (2 self)
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When answering queries using external information sources, their contents can be described by views. To answer a query, we must rewrite it using the set of views presented by the sources. When the external information sources also have the ability to answer some (perhaps limited) sets of queries that require performing operations on their data, the set of views presented by the source may be infinite (albeit encoded in some finite fashion). Previous work on answering queries using views has only considered the case where the set of views is finite. In order to exploit the ability of information sources to answer more complex queries, we consider the problem of answering conjunctive queries using infinite sets of conjunctive views. Our first result is that an infinite set of conjunctive views can be partitioned into a finite number of equivalence classes, such that picking one view from every nonempty class is sufficient to determine whether the query can be answered using the views. Se...
On Preserving Views In Evolving Environments
- In Proceedings of 4th Int. Workshop on Knowledge Representation Meets Databases (KRDB'97): Intelligent Access to Heterogeneous Information
, 1997
"... The construction and maintenance of data warehouses (views) in large-scale environments composed of numerous distributed information sources (ISs) such as the WWW has received great attention recently. Such environments are plagued with continuously changing information because ISs tend to continuou ..."
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Cited by 26 (17 self)
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The construction and maintenance of data warehouses (views) in large-scale environments composed of numerous distributed information sources (ISs) such as the WWW has received great attention recently. Such environments are plagued with continuously changing information because ISs tend to continuously evolve by modifying not only their content but also their query capabilities and interface and by joining or leaving the environment at any time. In this paper, we outline our position on issues related to the challenging new problem of how to adapt views in such evolving environments. We first present a taxonomy of view adaptation problems by describing the dimensions along which view adaptation problems can be classified. Based on this taxonomy, we identify a new view adaptation problem for view evolution in the context of ISs capability changes, which we call View Synchronization. We also outline the Evolvable View Environment (EVE) that we propose as framework for solving the view sy...
