Mirian Halfeld Ferrari Alves

Updates and Incremental Validation of XML Documents

We consider the incremental validation of updates on XML documents. When a valid XML document (i.e., one satisfying some constraints) is updated, it has to be verified that the new document still conforms to the imposed constraints. Incremental validation of updates leads to significant savings on computing time when compared to brute-force validation of an updated document from scratch.

Schema Evolution for XML: A Consistency-Preserving Approach

This paper deals with updates of XML documents that satisfy a given schema, e.g., a DTD. In this context, when a given update violates the schema, it might be the case that this update is accepted, thus implying to change the schema. Our method is intended to be used by a data administrator who is an expert in the domain of application of the database, but who is not required to be a computer science expert. Our approach consists in proposing different schema options that are derived from the original one. The method is consistency-preserving: documents valid with respect to the original schema remain valid. The schema evolution is implemented by an algorithm (called GREC) that performs changes on the graph of a finite state automaton and that generates regular expressions for the modified graphs. Each regular expression proposed by GREC is a choice of schema given to the administrator.

Efficient maintenance of temporal data warehouses

A temporal data warehouse can be defined as a set V of materialized views over non-temporal sources. We present a self-maintainable temporal data warehouse that, besides a set of temporal views V, has two kinds of auxiliary views: a set T of auxiliary relations containing only temporal information necessary to maintain the data warehouse and a set C of complements allowing the warehouse maintenance without consulting the source databases. Several features of our approach make it especially attractive as a maintenance method for warehouses: the entire history of source databases is not stored in the warehouse; the warehouse keeps enough information for its self-maintenance; and the warehouse maintenance is achieved by executing only relational algebra operators (i.e. non-temporal operators). Although temporal views in V are specified in a temporal algebraic query language we translate them into relational algebra expressions containing only auxiliary relations in T and complements in C. We claim that our method which extends some new techniques, can simplify considerably the implementation of a temporal data warehouse.

Approximate reasoning for real-time probabilistic processes

We develop a pseudo-metric analogue of bisimulation for generalized semiMarkov processes. The kernel of this pseudo-metric corresponds to bisimulation; thus we have extended bisimulation for continuous-time probabilistic processes to a much broader class of distributions than exponential distributions. This pseudo-metric gives a useful handle on approximate reasoning in the presence of numerical information - such as probabilities and time - in the model. We give a fixed point characterization of the pseudo-metric. This makes available coinductive reasoning principles for reasoning about distances. We demonstrate that our approach is insensitive to potentially ad hoc articulations of distance by showing that it is intrinsic to an underlying uniformity. We provide a logical characterization of this uniformity using a real-valued modal logic. We show that several quantitative properties of interest are continuous with respect to the pseudo-metric. Thus, if two processes are metrically close, then observable quantitative properties of interest are indeed close.

Business to Business Transaction Modeling and WWW Support

The information systems that support Electronic Commerce on the Internet are becoming more common and complex. The complexity of these systems increases the need for new models with different degrees of abstraction in order to simplify the visualization of different aspects of the structure, constraints and operation of the software. In this paper we discuss some aspects of the Electronic Commerce transactions presented in the literature. Our first contribution is to organize in a conceptual and logical level some models presented in the literature. We describe an Electronic Commerce application using these models and we discuss some aspects of a prototype that we are currently developing. The proposed models are useful not only to describe but also to support the adoption of new aspects in the applications. Another contribution is to demonstrate, in the context of the proposed models, the use of Automated Trust Negotiation.