Towards an Efficient Evaluation of General Queries

Database applications often require to evaluate queries containing quantifiers or disjunctions, e.g., for handling general integrity constraints. Existing efficient methods for processing quantifiers depart from the relational model as they rely on non-algebraic procedures. Looking at quantified query evaluation from a new angle, we propose an approach to process quantifiers that makes use of relational algebra operators only. Our approach performs in two phases. The first phase normalizes the queries producing a canonical form. This form permits to improve the translation into relational algebra performed during the second phase. The improved translation relies on a new operator - the complement-join - that generalizes the set difference, on algebraic expressions of universal quantifiers that avoid the expensive division operator in many cases, and on a special processing of disjunctions by means of constrained outer-joins. Our method achieves an efficiency at least comparable with that of previous proposals, better in most cases. Furthermore, it is considerably simpler to implement as it completely relies on relational data structures and operators

A rewriting logic approach to the formal specification and verification of web applications

[EN] This paper develops a Rewriting Logic framework for the automatic specification and verification of Web applications that considers the critical aspects of concurrent Web interactions, browser navigation features (e.g., forward/back-ward navigation, page refresh, and new window/tab opening), and Web script evaluation. By encompassing the main features of the most popular Web scripting languages (e.g., PHP, ASP, and Java Servlets), our scripting language is powerful enough to model the dynamics of complex Web applications, where the interactions among Web servers and Web browsers are formalized through a landmark communicating protocol that abstracts HTTP. We provide a detailed characterization of browser actions via rewrite rules and show how our models can be naturally model-checked by using the Linear Temporal Logic of Rewriting (LTLR), which is a Linear Temporal Logic that is specifically designed for model-checking rewrite theories. The framework has been completely implemented in Maude, and we report on some successful experiments that we conducted using the Maude LTLR model-checker.This work has been partially supported by the EU (FEDER) and the Spanish MEC project ref. TIN2010-21062-C02-02, and by Generalitat Valenciana ref. PROMETE02011/052. This work was carried out during the tenure by Demis Ballis of an ERCIM "Alain Bensoussan" Postdoctoral Fellowship. The research leading to these results has received funding from the European Union Seventh Framework Programme (FP7/2007-2013) under grant agreement no 246016. Daniel Romero was partially supported by FPI-MEC grant BES-2008-004860.Alpuente Frasnedo, M.; Ballis, D.; Romero, DO. (2014). A rewriting logic approach to the formal specification and verification of web applications. Science of Computer Programming. 81:79-107. https://doi.org/10.1016/j.scico.2013.07.014S791078

“AccessBIM” - A Model of Environmental Characteristics for Vision Impaired Indoor Navigation and Way Finding

The complexity of modern indoor environments has made navigation difficult for individuals with vision impairment. Hence, this thesis presents the AccessBIM framework, which is an optimized database that’s facilitates generation of a real-time floor plan with path determination. The AccessBIM framework has the potential to play an integral role in improving the independence and quality of life for people with vision impairment whilst also decreasing the cost to the community related to caretakers