Mapping-equivalence and oid-equivalence of single-function object-creating conjunctive queries

Conjunctive database queries have been extended with a mechanism for object creation to capture important applications such as data exchange, data integration, and ontology-based data access. Object creation generates new object identifiers in the result, that do not belong to the set of constants in the source database. The new object identifiers can be also seen as Skolem terms. Hence, object-creating conjunctive queries can also be regarded as restricted second-order tuple-generating dependencies (SO tgds), considered in the data exchange literature. In this paper, we focus on the class of single-function object-creating conjunctive queries, or sifo CQs for short. We give a new characterization for oid-equivalence of sifo CQs that is simpler than the one given by Hull and Yoshikawa and places the problem in the complexity class NP. Our characterization is based on Cohen's equivalence notions for conjunctive queries with multiplicities. We also solve the logical entailment problem for sifo CQs, showing that also this problem belongs to NP. Results by Pichler et al. have shown that logical equivalence for more general classes of SO tgds is either undecidable or decidable with as yet unknown complexity upper bounds.Comment: This revised version has been accepted on 11 January 2016 for publication in The VLDB Journa

Keyword search in the Deep Web

The Deep Web is constituted by data accessible through Web pages, but not readily indexable by search engines, as they are returned in dynamic pages. In this paper we propose a framework for accessing Deep Web sources, represented as relational tables with so-called ac- cess limitations, with keyword-based queries. We formalize the notion of optimal answer and investigate methods for query processing. To our knowledge, this problem has never been studied in a systematic way

Processing keyword queries under access limitations

The Deep Web is constituted by data accessible through Web pages, but not readily indexable by search engines, as they are returned in dynamic pages. In this paper we propose a framework for accessing Deep Web sources, represented as relational tables with so-called access limitations, with keyword-based queries. We formalize the notion of optimal answer and propose methods for query processing. To the best of our knowledge, ours is the first systematic approach to keyword search in such context

XWeB: the XML Warehouse Benchmark

With the emergence of XML as a standard for representing business data, new decision support applications are being developed. These XML data warehouses aim at supporting On-Line Analytical Processing (OLAP) operations that manipulate irregular XML data. To ensure feasibility of these new tools, important performance issues must be addressed. Performance is customarily assessed with the help of benchmarks. However, decision support benchmarks do not currently support XML features. In this paper, we introduce the XML Warehouse Benchmark (XWeB), which aims at filling this gap. XWeB derives from the relational decision support benchmark TPC-H. It is mainly composed of a test data warehouse that is based on a unified reference model for XML warehouses and that features XML-specific structures, and its associate XQuery decision support workload. XWeB's usage is illustrated by experiments on several XML database management systems

Composition with Target Constraints

It is known that the composition of schema mappings, each specified by source-to-target tgds (st-tgds), can be specified by a second-order 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). 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). Similarly, we prove unnesting results for st-SO dependencies, with the same types of consequences.Comment: This paper is an extended version of: M. Arenas, R. Fagin, and A. Nash. Composition with Target Constraints. In 13th International Conference on Database Theory (ICDT), pages 129-142, 201

Chapter The Value Proposition of Organizations for Young Graduates and their Employability

Certain young people are being propelled towards a more promising future than in the past, due to – amongst other things – continuous learning, which guarantees their productive capabilities. Employers are called upon to arrange a cogent value proposition to support young people in their constant growth that would also help them create an autonomous professional identit

The Evolution of the City of Timmins: A Single-Industry Community

The purpose of the thesis was to historically trace the development of a single-industry community, Timmins, Ontario. Five time periods were studied beginning with the incorporation of the Town of Timmins in 1912 and ending with the time period 1973 to 1977. Three aspects of economic development were used to analyze the growth of Timmins. The economic base of the town was analyzed in order to gain a better understanding of the sources of income and employment because these two elements in turn influenced demographic factors and the development of other sectors of the Timmins economy. The second aspect was a study of the demographic characteristics of the community. The third aspect of economic development was transportation and communication. These were studied to determine whether they were adequate to serve Timmins in light of its isolated location and whether the existence of these transportation and communication facilities aided or deterred to total development of Timmins. The possibility of developing visible secondary industry in Timmins was analyzed using seven essential industrial location factors. Also, four models for urban growth were examined to indicate whether they were applicable to Timmins during the various time periods. The thesis effectively traced the development of Timmins and indicated the effect that the three aspects of economic development had on the total growth of the community. Timmins’ viability was dependent upon the fluctuations in the strength of its economic base and this specified the need for more diversification. The problems associated with diversification are clearly illustrated throughout this thesis. Finally, by the end of 1977, it was found that Timmins had developed within the constraints of a northern location and in accordance with the prosperity of the primary sector. The evolution of Timmins from a frontier town to a regional center resulted from the growth of the mining industry in the region