Emmanuel Waller

Object migration

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.

Polymorphic Type Inference for the Relational Algebra

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 of 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 and polymorphic expressive power.

Type inference in the polymorphic relational algebra

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.

Data-Driven Publication of Relational Databases

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

Report on the EDBT/ICDT 2010 workshop on updates in XML

The first international workshop on Updates in XML [1] was held in conjunction with the EDBT/ICDT conference in Lausanne (Switzerland) on March 22, 2010, and attracted approximately 25 participants, culminating with about 40 attending the last session. This paper summarizes the main ideas presented in the workshop as well as interesting perspectives identified by the participants.

On the expressive power of update primitives

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 SQLs 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.