Querying Data Sources that Export Infinite Sets of Views

Cautis, Bogdan; Deutsch, Alin; Onose, Nicola

doi:10.1007/s00224-010-9293-4

Cited by 4 publications

(13 citation statements)

References 25 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…relational setting [9,16,6], but has not been addressed for sources that publish XML data (as is the case for most current Web Services). Since our focus is on practical algorithms, we consider sources that make XML data available through sets of views belonging to an XPath fragment for which the basic building blocks of rewriting algorithms, namely containment and equivalence, are tractable [11].…”

Section: Introductionmentioning

confidence: 99%

“…Expressibility and support. As in the literature on sources exporting sets of legal relational queries [16,6], we consider two settings for query answering. The first one is when the client query has to be fully answered by asking one legal query over the source, with no post-processing of its result.…”

Section: Introductionmentioning

confidence: 99%

“…The first one is when the client query has to be fully answered by asking one legal query over the source, with no post-processing of its result. The corresponding decision problem is called expressibility [6]: we say that query q is expressible if it is equivalent to a view published by the source. The second setting is when the capabilities of the source are extended by a source wrapper [13] that intercepts the client query, finds an equivalent rewriting for it in terms of the views, post-processes the results locally and returns the query result to the client.…”

Section: Introductionmentioning

confidence: 99%

“…The second setting is when the capabilities of the source are extended by a source wrapper [13] that intercepts the client query, finds an equivalent rewriting for it in terms of the views, post-processes the results locally and returns the query result to the client. The associated problem is called support [6]: given a rewriting query language LR, q is supported by P if it has an equivalent rewriting in LR using some finite set of legal queries supported by the source.…”

Section: Introductionmentioning

confidence: 99%

“…This is a consequence of previous results [5], showing that rewriting XPath using an intersection of XPath views (a problem subsumed by support) is already coNP-hard. This is a major difference with respect to the relational case, in which support and expressibility were proven inter-reducible [6]. Since our focus is on practical algorithms, we propose a PTIME algorithm for id-based support that is sound for any XPath query, and becomes complete under fairly permissive restrictions on the query, without further restricting the language of the views.…”

Section: Introductionmentioning

confidence: 99%

See 4 more Smart Citations

Efficient rewriting of XPath queries using Query Set Specifications

et al. 2009

Self Cite

View full text Add to dashboard Cite

We study the problem of querying XML data sources that accept only a limited set of queries, such as sources accessible by Web services which can implement very large (potentially infinite) families of XPath queries. To compactly specify such families of queries we adopt the Query Set Specifications [14], a formalism close to context-free grammars.We say that query Q is expressible by the specification P if it is equivalent to some expansion of P. Q is supported by P if it has an equivalent rewriting using some finite set of P's expansions. We study the complexity of expressibility and support and identify large classes of XPath queries for which there are efficient (PTIME) algorithms. Our study considers both the case in which the XML nodes in the results of the queries lose their original identity and the one in which the source exposes persistent node ids.

show abstract

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

Efficient rewriting of XPath queries using Query Set Specifications

et al. 2009

Self Cite

View full text Add to dashboard Cite

show abstract

Composition with target constraints

Arenas

Fagin

Nash³

2010

Proceedings of the 13th International Conference on Database Theory

View full text Add to dashboard Cite

It is known that the composition of schema mappings, each specified by source-to-target tgds (st-tgds), can be specified by a secondorder tgd (SO tgd). We consider the question of what happens when target constraints are allowed. Specifically, we consider the question of specifying the composition of standard schema mappings (those specified by st-tgds, target egds, and a weakly-acyclic set of target tgds). We show that SO tgds, even with the assistance of arbitrary source constraints and target constraints, cannot specify in general the composition of two standard schema mappings. Therefore, we introduce source-to-target second-order dependencies (st-SO dependencies), which are similar to SO tgds, but allow equations in the conclusion. We show that st-SO dependencies (along with target egds and target tgds) are sufficient to express the composition of every finite sequence of standard schema mappings, and further, every st-SO dependency specifies such a composition. In addition to this expressive power, we show that st-SO dependencies enjoy other desirable properties. In particular, they have a polynomial-time chase that generates a universal solution. This universal solution can be used to find the certain answers to unions of conjunctive queries in polynomial time.It is easy to show that the composition of an arbitrary number of standard schema mappings is equivalent to the composition of only two standard schema mappings. We show that surprisingly, the analogous result holds also for schema mappings specified by just st-tgds (no target constraints). That is, the composition of an arbitrary number of such schema mappings is equivalent to the composition of only two such schema mappings. This is proven by showing that every SO tgd is equivalent to an unnested SO tgd (one where there is no nesting of function symbols). The language of unnested SO tgds is quite natural, and we show that unnested SO tgds are capable of specifying the composition of an arbitrary number of schema mappings, each specified by st-tgds. Similarly, we prove unnesting results for st-SO dependencies, with the same types of consequences.The collapsing result for SO tgds gives us two alternative ways to deal with the composition of multiple schema mappings specified Permission to make digital or hard copies of all or part of this work for personal or classroom use is granted without fee provided that copies are not made or distributed for profit or commercial advantage and that copies bear this notice and the full citation on the first page. To copy otherwise, to republish, to post on servers or to redistribute to lists, requires prior specific permission and/or a fee. ICDT 2010, March 22-25, 2010, Lausanne, Switzerland. Copyright 2010 by st-tgds. First, we can replace the composition by a single schema mapping, specified by an unnested SO tgd. Second, we can replace the composition by the composition of only two schema mappings, each specified by st-tgds. A similar comment holds for the composition of standard schema mappings.

show abstract

Active knowledge

Preda

Kasneci

Suchanek

et al. 2010

Proceedings of the 2010 ACM SIGMOD International Conference on Management of Data

View full text Add to dashboard Cite

The proliferation of knowledge-sharing communities and the advances in information extraction have enabled the construction of large knowledge bases using the RDF data model to represent entities and relationships. However, as the Web and its latently embedded facts evolve, a knowledge base can never be complete and up-to-date. On the other hand, a rapidly increasing suite of Web services provide access to timely and high-quality information, but this is encapsulated by the service interface. We propose to leverage the information that could be dynamically obtained from Web services in order to enrich RDF knowledge bases on the fly whenever the knowledge base does not suffice to answer a user query.To this end, we develop a sound framework for appropriately generating queries to encapsulated Web services and efficient algorithms for query execution and result integration. The query generator composes sequences of function calls based on the available service interfaces. As Web service calls are expensive, our method aims to reduce the number of calls in order to retrieve results with sufficient recall. Our approach is fully implemented in a complete prototype system named ANGIE 1 . The user can query and browse the RDF knowledge base as if it already contained all the facts from the Web services. This data, however, is gathered and integrated on the fly, transparently to the user. We demonstrate the viability and efficiency of our approach in experiments based on real-life data provided by popular Web services.

show abstract

Querying Data Sources that Export Infinite Sets of Views

Cited by 4 publications

References 25 publications

Efficient rewriting of XPath queries using Query Set Specifications

Efficient rewriting of XPath queries using Query Set Specifications

Composition with target constraints

Active knowledge

Contact Info

Product

Resources

About