Anne Doucet

Thémis: a database programming language handling integrity constraints

This article presents a database programming language, Thémis, which supports subtyping and class hierarchies, and allows for the definition of integrity constraints in a global and declarative way. We first describe the salient features of the language: types, names, classes, integrity constraints (including methods), and transactions. The inclusion of methods into integrity constraints allows an increase of the declarative power of these constraints. Indeed, the information needed to define a constraint is not always stored in the database through attributes, but is sometimes computed or derived data. Then, we address the problem of efficiently checking constraints. More specifically, we consider two different problems: (1) statically reducing the number of constraints to be checked, and (2) generating an efficient run-time checker. Using simple strategies, one can significantly improve the efficiency of the verification. We show how to reduce the number of constraints to be checked by characterizing the portions of the database that are involved in both the constraints and in a transaction. We also show how to generate efficient algorithms for checking a large class of constraints. We show how all the techniques presented exploit the underlying type system, which provides significant help in solving (1) and (2). Last, the current status of the Thémis prototype is presented.

Using Database Versions to Implement Temporal Integrity Constraints

This paper presents the extension of integrity constraint mechanisms for maintaining consistency in temporal databases, when both transaction time and valid time are taken into account. This work is based on the database version model, in which consistency is maintained using adequate integrity constraints called mv-constraints. The issue of describing and classifying temporal constraints and the issue of defining them on top of the database version model, by mapping them to mv-constraints, are both addressed.

Thémis: a database programming language with integrity constraints

This paper is concerned with the problem of efficiently checking of integrity constraints in data base programming languages supporting subtyping and class hierarchies. More specifically, we consider two different problems: (1) statically reduce the number of constraints to be checked, and (2) generate an efficient run time checker. Using simple strategies, one can significantly improve the efficiency of the verification. We show how to reduce the number of constraints to be checked by characterising the portions of the database that are concerned by the constraints and involved in a transaction. We also show how to generate efficient algorithms for checking a large class of constraints. We show how all the techniques presented took great advantage of the underlying type system which provide a significant help both in solving (1) and (2). Last the current status of the Themis prototype is presented.

Extending OAI-PMH over structured P2P networks for digital preservation

Open archives initiative (OAI) allows both libraries and museums create and share their own low-cost digital libraries (DL). OAI DL are based on OAI-PMH protocol which, although is consolidated as a pattern for disseminating metadata, does not rely on either digital preservation and availability of content, essential requirements in this type of system. Building new mechanisms that guarantee improvements, at no or low cost increases, becomes a great challenge. This article proposes a distributed archiving system based on a P2P network, that allows OAI-based libraries to replicate digital objects to ensure their reliability and availability. The proposed system keeps and extends the current OAI-PMH protocol characteristics and is designed as a set of OAI repositories, where each repository has an independent fail probability assigned to it. Items are inserted with a reliability that is satisfied by replicating them in subsets of repositories. Communication between the nodes (repositories) of the network is organized in a distributed hash table and multiple hash functions are used to select repositories that keep the replicas of each stored item. The OAI characteristics combined with a structured P2P digital preservation system allow the construction of a reliable and totally distributed digital library. The archiving system has been evaluated through experiments in a real environment and the OAI-PMH extension validated by the implementation of a proof-of-principle prototype.

Thematic Schema Building for Mediation-based Peer-to-Peer Architecture

Recently, mediation tools and peer-to-peer systems have allowed an important evolution for data sharing. Mediators are now mature techniques to share structured and heterogeneous data distributed through a reasonable number of nodes. Peer-to-peer architectures open new ways to build very large and dynamic networks allowing to share unstructured data as files indexed by some keywords. We propose here to exploit the complementarity of these approaches to efficiently share structured and heterogeneous data distributed through a large set of nodes. We propose an unstructured peer-to-peer architecture handling interactions between a large set of mediators and simplifying the process of schema exchanges. We focus on the dynamic building of mediation schemas which are personalized for user needs in order to query the network. To validate our approach, we have implemented a prototype, MenT2, which integrates several schemas via mediator interactions in a simulated network.

Cluster Entries for Semantic Organization of Peer-to-Peer Network

Techniques of pure flooding queries through a peer-to-peer network[1] reach their limits for data localization which are not replicated and stored through a high number of nodes. To improve implicitly the query routing towards relevant nodes in order to smartly recover all the relevant data, we propose to organize a peer-to-peer network in which the logical neighborhood of each node is built according to the semantic of its content. Indeed, the data we target, are semantically rich, easily classifiable with a field of interest, or a theme (e.g. “rock”, “jazz”, ...in music, or “hydrology”, “oceanography”,...in sciences of environment). The motivation of our approach is based on the fact users/providers query the network on the theme of the data they store. Thus, if a node contains many data about the theme “Hydrology”, the query propagation is more efficient, if the neighbors of this node contain data about “Hydrology”. In the prototype VENISE (serVicE for Node Insertion in Semantic clustErs), we propose a protocol of node insertion based on cluster entries to cluster a peer-to-peer network.