KD2R: a Key Discovery method for semantic Reference Reconciliation in OWL

The reference reconciliation problem consists of deciding whether different identifiers refer to the same world entity. Some existing reference reconciliation approaches use key constraints to infer reconciliation decisions. In the context of the Linked Open Data, this knowledge is not available. In this master thesis we propose KD2R, a method which allows automatic discovery of key constraints associated to OWL2 classes. These keys are discovered from RDF data which can be incomplete. The proposed algorithm allows this discovery without having to scan all the data. KD2R has been tested on data sets of the international contest OAEI and obtains promising results.Le problème de réconciliation de référence consiste à décider si des identifiants différents référé à la même entité du monde réel. Certaines approches de réconciliation de référence utilisent des contraintes des clé pour déduire des décisions de réconciliation des références. Dans le contexte des données liées, cette connaissance n'est pas disponible. Dans ce stage de master nous proposons KD2R, une méthode qui permet la découverte automatique des contraintes de clé associées à des classes OWL2. Cette contraintes de cl'e sont découvertes a' partir de données RDF qui peuvent être incomplètes. L'algorithme propos'e permet cette découverte, sans avoir à passer en revue toutes les données. KD2R a été testé sur des jeux de données du concours international OAEI et obtient des résultats prometteurs

UvA-DARE (Digital Academic Repository) Uncertain Data Integration Using Functional Dependencies

Abstract. Data integration systems are crucial for applications that need to provide a uniform interface to a set of autonomous and heterogeneous data sources. However, setting up a full data integration system for many application contexts, e.g. web and scientific data management, requires significant human effort which prevents it from being really scalable. In this paper, we propose IFD (Integration based on Functional Dependencies), a pay-as-you-go data integration system that allows integrating a given set of data sources, as well as incrementally integrating additional sources. IFD takes advantage of the background knowledge implied within functional dependencies for matching the source schemas. Our system is built on a probabilistic data model that allows capturing the uncertainty in data integration systems. Our performance evaluation results show significant performance gains of our approach in terms of recall and precision compared to the baseline approaches. They confirm the importance of functional dependencies and also the contribution of using a probabilistic data model in improving the quality of schema matching. The analytical study and experiments show that IFD scales well

On the Discovery of Semantically Meaningful SQL Constraints from Armstrong Samples: Foundations, Implementation, and Evaluation

A database is said to be C-Armstrong for a finite set Σ of data dependencies in a class C if the database satisfies all data dependencies in Σ and violates all data dependencies in C that are not implied by Σ. Therefore, Armstrong databases are concise, user-friendly representations of abstract data dependencies that can be used to judge, justify, convey, and test the understanding of database design choices. Indeed, an Armstrong database satisfies exactly those data dependencies that are considered meaningful by the current design choice Σ. Structural and computational properties of Armstrong databases have been deeply investigated in Codd’s Turing Award winning relational model of data. Armstrong databases have been incorporated in approaches towards relational database design. They have also been found useful for the elicitation of requirements, the semantic sampling of existing databases, and the specification of schema mappings. This research establishes a toolbox of Armstrong databases for SQL data. This is challenging as SQL data can contain null marker occurrences in columns declared NULL, and may contain duplicate rows. Thus, the existing theory of Armstrong databases only applies to idealized instances of SQL data, that is, instances without null marker occurrences and without duplicate rows. For the thesis, two popular interpretations of null markers are considered: the no information interpretation used in SQL, and the exists but unknown interpretation by Codd. Furthermore, the study is limited to the popular class C of functional dependencies. However, the presence of duplicate rows means that the class of uniqueness constraints is no longer subsumed by the class of functional dependencies, in contrast to the relational model of data. As a first contribution a provably-correct algorithm is developed that computes Armstrong databases for an arbitrarily given finite set of uniqueness constraints and functional dependencies. This contribution is based on axiomatic, algorithmic and logical characterizations of the associated implication problem that are also established in this thesis. While the problem to decide whether a given database is Armstrong for a given set of such constraints is precisely exponential, our algorithm computes an Armstrong database with a number of rows that is at most quadratic in the number of rows of a minimum-sized Armstrong database. As a second contribution the algorithms are implemented in the form of a design tool. Users of the tool can therefore inspect Armstrong databases to analyze their current design choice Σ. Intuitively, Armstrong databases are useful for the acquisition of semantically meaningful constraints, if the users can recognize the actual meaningfulness of constraints that they incorrectly perceived as meaningless before the inspection of an Armstrong database. As a final contribution, measures are introduced that formalize the term “useful” and it is shown by some detailed experiments that Armstrong tables, as computed by the tool, are indeed useful. In summary, this research establishes a toolbox of Armstrong databases that can be applied by database designers to concisely visualize constraints on SQL data. Such support can lead to database designs that guarantee efficient data management in practice