A Maude specification of the Kademlia distributed hash table: centralized version

Kademlia is the most popular peer-to-peer distributed hash table (DHT) currently in use. It offers a number of desirable features that result from the use of a notion of distance between objects based on the bitwise exclusive or of n-bit quantities that represent both nodes and files. Nodes keep information about files close or near to them in the key space and the search algorithm is based on looking for the closest node to the file key. The structure of the routing table defined in each peer guarantees that the lookup algorithm takes no longer than logn steps. We have developed a formal specification of a P2P network that uses the Kademlia DHT in the Maude language. We use sockets to connect different Maude instances and create a P2P network where the Kademlia protocol can be used, hence providing an implementation of the protocol which is correct by design. Then, we show how to abstract this system in order to analyze it using Real-Time Maude. The model is fully parameterized regarding the time taken by the different actions to facilitate the analysis of various scenarios. Finally, we use time-bounded model-checking and exhaustive search to prove properties of the protocol over different scenarios. This report focuses on the implementation details of the centralized specification

A Declarative Debugger for Maude Specifications: User Guide

We show in this guide how to use our declarative debugger for Maude specifications. Declarative debugging is a semi-automatic technique that starts from a computation considered incorrect by the user (error symptom) and locates a program fragment responsible for the error by asking questions to an external oracle, which is usually the user. In our case the debugging tree is obtained from a proof tree in a suitable semantic calculus; more concretely, we abbreviate the proof trees obtained from this calculus in order to ease and shorten the debugging process while preserving the correctness and completeness of the technique. We present the main features of our tool, what is assumed about the modules introduced by the user, the list of available commands, and the kinds of questions used during the debugging process. Then, we use several examples to illustrate how to use the debugger. We refer the interested reader to the webpage http://maude.sip.ucm.es/debugging, where these and other examples can be found together with more information about the theory underlying the debugger, its implementation and the Maude source files

Implementación de un sistema para el aprendizaje de lenguajes de programación mediante tutoriales interactivos

Depto. de Sistemas Informáticos y ComputaciónFac. de InformáticaFALSEsubmitte

Singular and Plural Functions for Functional Logic Programming

Functional logic programming (FLP) languages use non-terminating and non-confluent constructor systems (CS's) as programs in order to define non-strict non-determi-nistic functions. Two semantic alternatives have been usually considered for parameter passing with this kind of functions: call-time choice and run-time choice. While the former is the standard choice of modern FLP languages, the latter lacks some properties---mainly compositionality---that have prevented its use in practical FLP systems. Traditionally it has been considered that call-time choice induces a singular denotational semantics, while run-time choice induces a plural semantics. We have discovered that this latter identification is wrong when pattern matching is involved, and thus we propose two novel compositional plural semantics for CS's that are different from run-time choice. We study the basic properties of our plural semantics---compositionality, polarity, monotonicity for substitutions, and a restricted form of the bubbling property for constructor systems---and the relation between them and to previous proposals, concluding that these semantics form a hierarchy in the sense of set inclusion of the set of computed values. We have also identified a class of programs characterized by a syntactic criterion for which the proposed plural semantics behave the same, and a program transformation that can be used to simulate one of them by term rewriting. At the practical level, we study how to use the expressive capabilities of these semantics for improving the declarative flavour of programs. We also propose a language which combines call-time choice and our plural semantics, that we have implemented in Maude. The resulting interpreter is employed to test several significant examples showing the capabilities of the combined semantics. To appear in Theory and Practice of Logic Programming (TPLP)Comment: 53 pages, 5 figure

Herramienta interactiva de manipulación y corrección de entregas de ejercicios en asignaturas con evaluación continua

En este proyecto se extiende el conjunto de herramientas del proyecto Innova-Docencia nº 49 (2016/2017) introduciendo un asistente que permite, de modo interactivo, navegar y realizar operaciones por lotes en todas las entregas de un mismo ejercicio

Juez automático para el aprendizaje de bases de datos

Proponemos desarrollar un juez automático para el aprendizaje de bases de datos. Este sistema web permitirá a los estudiantes practicar con diferentes ejercicios de bases de datos desde casa y recibir retroalimentación inmediata sobre los fallos

Tutoriales interactivos para el estudio de la programación: impacto en el aprendizaje

Depto. de Sistemas Informáticos y ComputaciónFac. de InformáticaFALSEsubmitte