More and more datasets are currently connected by identity links using properties such as owl:sameAs expressed in OWL. Identity links are statements that declare that two resources refer to the same real-world entity. However, we cannot attest the correctness of all identity links. Without a central name authority, most identity links are generated by heuristics and they are not reviewed by experts. The main issue in invalidating identity links is the heterogeneity of datasets, they commonly do not share the same predicates. Furthermore, the description of the resources can be incomplete. Despite how the resources are described, identity links are necessary to link data for posterior use. In this paper, we present a framework to invalidate identity links by dissimilarity and outlier detection in equivalence classes of identity links.

The SQL standard offers three primitive operations (insert, delete, and update which is here called modify) to update a relation based on a generic query. This paper compares the expressiveness of programs composed of these three operations, with the general notion of update that simply replaces the content of the relation by the result of a query. It turns out that replacing cannot be expressed in terms of insertions, deletions, and modifications, and neither can modifications be expressed in terms of insertions and deletions. The expressive power gained by if-then-else control flow in programs is investigated as well. Different ways to perform replacing are discussed: using a temporary variable; using the new SQL merge operation; using SQL's data change delta tables; or using queries involving object creation or arithmetic. Finally the paper investigates the power of alternating the different primitives. For example, an insertion followed by a modification cannot always be expressed as a modification followed by an insertion.

We present in this paper an approach for XQuery optimization that exploits minimization opportunities raised in composition-style nesting of queries. More precisely, we consider the simplification of XQuery queries in which the intermediate result constructed by a subexpression is queried by another subexpression. Based on a large subset of XQuery, we describe a rule-based algorithm that recursively prunes query expressions, eliminating useless intermediate results. Our algorithm takes as input an XQuery expression that may have navigation within its subexpressions and outputs a simplified, equivalent XQuery expression, and is thus readily usable as an optimization module in any existing XQuery processor. We demonstrate by experiments the impact of our rewriting approach on query evaluation costs and we prove formally its correctness.

The paper presents a framework for publishing relational databases in textual documents such as mails, HTML pages, LATEX or BibTex files, plain texts, etc. The publication process relies on a mapping of the relational database to a virtual data graph which supports navigation operators. Applications can express the data they need by navigating in the graph. These operations are provided by a declarative query language over virtual graphs, named DOCQL. We illustrate its features with the conference management system MYREVIEW

We give a polymorphic account of the relational algebra.We introduce a formalism of "type formulas" specifically tuned for relational algebra expressions, and present an algorithm that computes the ".principal" type for a given expression.The principal type ojF an expression is a formula that specifies, in a clear and concise manner, all assignments of types (sets of attributes) tO relation names, under which a given relational algebra expression is well-typed, as well as the output type that expression will have under each of these assignments.Topics discussed include complexity, the relationship with monadic logic, and polymorphic expressive power.

We study a mechanism that supports the migration of objects from one class of an OODB to another, thereby enabling us to model the same object playing different roles throughout its lifetime. Object migration may introduce typing conflicts due to the different typing constraints imposed by the classes. We present a coercion-like adaptation process that automatically resolves these conflicts. The process combines re-classification of objects and modification of attributes. We study the computational complexity of the problem, and show that the adaptation process can be performed efficiently in databases with covariant schemas.

We show how classical datalog semantics can be used directly and very simply to provide semantics to a syntactic extension of datalog with methods, classes, inheritance, overloading and late binding. Several approaches to resolution are considered, implemented in the model, and formally compared. They range from resolution in C++ style to original kinds of resolution suggested by the declarative nature of the language. We show connections to view specification and a further extension allowing runtime derivation of the class hierarchy.

The concept of method schemas is proposed as a simple model for object-oriented programming with features such as classes with methods and inheritance, method name overloading, and late binding. An important issue is to check whether a given method schema can possibly lead to inconsistencies in some interpretations. The consistency problem for method schemas is studied. The problem is shown to be undecidable in general. Decidability is obtained for monadic and/or recursion-free method schemas. The effect of covariance is considered. The issues of incremental consistency checking and of a sound algorithm for the general case are briefly discussed.