Mapping between Alloy specifications and database implementations

The emergence of lightweight formal methods tools such as Alloy improves the software design process, by encouraging developers to model and verify their systems before engaging in hideous implementation details. However, an abstract Alloy specification is far from an actual implementation, and manually refining the former into the latter is unfortunately a non-trivial task. This paper identifies a subset of the Alloy language that is equivalent to a relational database schema with the most conventional integrity constraints, namely functional and inclusion dependencies. This semantic correspondence enables both the automatic translation of Alloy specifications into relational database schemas and the reengineering of legacy databases into Alloy. The paper also discusses how to derive an object-oriented application layer to serve as interface to the underlying database

Algebraic specialization of generic functions for recursive types

Defining functions over large, possibly recursive, data structures usually involves a lot of boilerplate. This code simply traverses non-interesting parts of the data, and rapidly becomes a maintainability problem. Many generic programming libraries have been proposed to address this issue. Most of them allow the user to specify the behavior just for the interesting bits of the structure, and provide traversal combinators to “scrap the boilerplate”. The expressive power of these libraries usually comes at the cost of efficiency, since runtime checks are used to detect where to apply the type-specific behavior. In previous work we have developed an effective rewrite system for specialization and optimization of generic programs. In this paper we extend it to also cover recursive data types. The key idea is to specialize traversal combinators using well-known recursion patterns, such as folds or paramorphisms. These are ruled by a rich set of algebraic laws that enable aggressive optimizations. We present a type-safe encoding of this rewrite system in Haskell, based on recent language extensions such as type-indexed type families

Calculating with lenses: optimising bidirectional transformations

This paper presents an equational calculus to reason about bidirectional transformations specified in the point-free style. In particular, it focuses on the so-called lenses as a bidirectional idiom, and shows that many standard laws characterising point-free combinators and recursion patterns are also valid in that setting. A key result is that uniqueness also holds for bidirectional folds and unfolds, thus unleashing the power of fusion as a program optimisation technique. A rewriting system for automatic lens optimisation is also presented, to prove the usefulness of the proposed calculus.(undefined

El capital como pretensión de totalidad

Reseña de: Gandarilla Salgado, José Guadalupe, Asedios a la totalidad. Poder y política en la modernidad desde un encare de-colonial, Barcelona, Anthropos, 2012, 354 pp

Títulos con respaldo de activos de tarjetas de crédito como instrumentos de transferencia de riesgo de crédito

This paper proposes an index for determining those banking institution in Mexico that should transfer their credit card portfolios risk credit through Asset Back-Securities (ABSs). This is done recurring to models for predicting insolvency developed by Robert Altman (1968) and Discriminant Analysis. As of financial ratios and financial health of banking institutions this research is able to characterize the credit card portfolio of banking institutions in Mexico.Transferencia de riesgo de crédito, productos derivados, tarjeta de crédito, análisis discriminante

Performance Assessment of IEEE 802.11a 54 Mbps WPA Laboratory Links

The importance of wireless communications, involving electronic devices, has been widely recognized.Performance is a fundamental issue, resulting in more reliable and efficient communications. Security is also critically important. Laboratory measurements were performed about several performance aspects of Wi-Fi IEEE 802.11a 54 Mbps WPA links. Our study contributes to performance evaluation of this technology, using available equipments (HP V-M200 access points and Linksys WPC600N adapters). New results are presented and discussed, namely at OSI level 4, from TCP and UDP experiments. TCP throughput is measured versus TCP packet length. Jitter and percentage datagram loss are measured versus UDP datagram size. Results are compared for both pointto point and four-node point-to-multipoint links. Conclusions are drawn about performance of the links.University of Beira Interiorinfo:eu-repo/semantics/publishedVersio

Performance Research on IEEE 802.11a 54 Mbps WPA2 Laboratory Links

The increasing importance of wireless communications, involving electronic devices, has been widely recognized. Performance is a fundamental issue, resulting in more reliable and efficient communications. Security is also crucially important. Laboratory measurements are presented about several performance aspects of Wi-Fi IEEE 802.11a 54 Mbps WPA2 point-to-point and point-to-multipoint links. Our study contributes to performance evaluation of this technology under WPA2 encryption, using available equipments (HP V-M200 access points and Linksys WPC600N adapters). New results are given from TCP and UDP experiments concerning TCP throughput versus TCP packet length, jitter and percentage datagram loss versus UDP datagram size. Comparisons are made to corresponding results for Open links. Conclusions are drawn about the comparative performance of the links.University of Beira Interiorinfo:eu-repo/semantics/publishedVersio

Towards a framework for multi-directional model transformations

The Query/View/Transformation Relations (QVT-R) standard for bidirectional model transformation is notorious for its underspecified semantics. When restricted to transformations between pairs of models, most of the ambiguities and omissions have been addressed in recent work. Nevertheless, the application of the QVT-R language is not restricted to that scenario, and similar issues remain unexplored for the multidirectional case (maintaining consistency between more than two models), that has been overlooked so far. In this paper we first discuss ambiguities and omissions in the QVT-R standard concerning the mutidirectional transformation scenario, and then propose a simple extension and formalization of the checking and enforcement semantics that clarifies some of them. We also discuss how such proposal could be implemented in our Echo bidirectional model transformation tool. Ours is just a small step towards making QVT-R a viable language for bidirectional transformation in realistic applications, and a considerable amount of basic research is still needed to fully accomplish that goal.(undefined