Query Rewriting with Symmetric Constraints

Koch, Christoph

doi:10.1007/3-540-45758-5_9

Cited by 20 publications

(14 citation statements)

References 17 publications

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“…The problem was generalized in [7] to replace views with schema mapping constraints from the source schema to the target schema, also allowing constraints on the target schema. [22] generalizes the setting even further, allowing schema mappings in both directions, and settling the problem by charting its decidability boundaries and providing tight complexity bounds.…”

Section: Other Considerationsmentioning

confidence: 99%

Query reformulation with constraints

2006

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Let Σ1, Σ2 be two schemas, which may overlap, C be a set of constraints on the joint schema Σ1 ∪ Σ2, and q1 be a Σ1-query. An (equivalent) reformulation of q1 in the presence of C is a Σ2-query, q2, such that q2 gives the same answers as q1 on any Σ1 ∪ Σ2-database instance that satisfies C. In general, there may exist multiple such reformulations and choosing among them may require, for example, a cost model. DisciplinesComputer Sciences Authors retain the right to post a pre-print version of the journal article on Internet web sites including electronic pre-print servers, and to retain indefinitely such version on such servers or sites. The right to post a revised personal version of the text of the final journal article (to reflect changes made in the peer review process) on the author's personal or institutional web site or server, incorporating the complete citation and with a link to the Digital Object Identifier (DOI) of the article.

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Section: Other Considerationsmentioning

confidence: 99%

Query reformulation with constraints

2006

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“…The first approach we discuss for assigning semantics to a P2P system, is the FOL approach, followed by [5,13,9]. In this approach, one associates to a P2P system S = (P, M) a single FOL theory, obtained as the union of the various peer theories, plus suitable FOL formulas corresponding to the P2P mapping assertions.…”

Section: Fol Semantics For P2p Systemsmentioning

confidence: 99%

“…-One of the implications of the above observation is that, even if we restrict the general framework in such a way that the various peers are decidable FOL theories (in particular, empty theories), query answering in the whole P2P system is actually undecidable, as illustrated in the next section. This is why, in [9,13], the authors propose syntactic restrictions on the mapping assertions (e.g., acyclicity).…”

Section: Fol Semantics For P2p Systemsmentioning

confidence: 99%

Semantic Data Integration in P2P Systems

Calvanese

Damaggio

Giacomo

et al. 2004

Databases, Information Systems, and Peer-to-Peer Computing

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Abstract. In this paper, we study the problem of data integration in P2P systems. Differently from the traditional setting, data integration in these systems is not based on the existence of a global view. Instead, each peer exports data in terms of its own schema, and information integration is achieved by establishing mappings among the various peer schemas. We present a framework that captures this general architecture, and then we discuss the problem of characterizing the semantics of such framework. We show that the usual approach of resorting to a first-order logic intepretation of P2P mappings, leads both to a poor modeling of the whole system, and to undecidability of query answering, even for mappings of a restricted form. This motivates the need of a new semantics for P2P system. We then present a novel proposal, based on epistemic logic, and show that not only it adequately models the interactions among peers, but it also supports decidable query answering. In particular, for the restricted form of mapping mentioned above, query answering is polynomial with respect to the size of data stored in the peers.

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“…Most of the research on query processing under schema mapping in data integration has concentrated on GAV mappings, and on LAV mappings under the label of view-based query processing (see, for instance the survey in [41]). In data integration, GLAV mappings have been specifically considered in [19,38,42], but only for the case of relational databases, and only for query answering and query rewriting. GLAV schema mappings have been mainly investigated in data exchange: in [9,32,33,47] the emphasis is on providing foundations for data exchange systems based on schema mappings, whereas in [11-14, 34-36, 48] the goal is to study operators on schema mappings relevant to model management, notably, composition, merge, and inverse.…”

Section: Introductionmentioning

confidence: 99%

Query processing under GLAV mappings for relational and graph databases

et al. 2012

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Schema mappings establish a correspondence between data stored in two databases, called source and target respectively. Query processing under schema mappings has been investigated extensively in the two cases where each target atom is mapped to a query over the source (called GAV, global-as-view), and where each source atom is mapped to a query over the target (called LAV, local-as-view). The general case, called GLAV, in which queries over the source are mapped to queries over the target, has attracted a lot of attention recently, especially for data exchange. However, query processing for GLAV mappings has been considered only for the basic service of query answering, and mainly in the context of conjunctive queries (CQs) in relational databases. In this paper we study query processing for GLAV mappings in a wider sense, considering not only query answering, but also query rewriting, perfectness (the property of a rewriting to compute exactly the certain answers), and query containment relative to a mapping. We deal both with the relational case, and with graph databases, where the basic querying mechanism is that of regular path queries. Query answering in GLAV can be smoothly reduced to a combination of the LAV and GAV cases, and for CQs this reduction can be exploited also for the remaining query processing tasks. In contrast, as we show, GLAV query processing for graph databases is non-trivial and requires new insights and techniques. We obtain upper bounds for answering, rewriting, and perfectness, and show decidability of relative containment.

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Query Rewriting with Symmetric Constraints

Cited by 20 publications

References 17 publications

Query reformulation with constraints

Query reformulation with constraints

Semantic Data Integration in P2P Systems

Query processing under GLAV mappings for relational and graph databases

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