Thesis--M. Phil., University of Hong Kong, 1986.

published_or_final_version / Computer Science / Master / Master of Philosophy

Η εργασία ασχολείται με τα Ασαφή Δίκτυα Petri. Αφού γίνει μιά ιστορική αναδρομή στα Δίκτυα Petri, στη συνέχεια αναπτύσονται τα διάφορα είδη δικτύων Petri καθώς επίσης και οι ιδιότητές τους. Επιπλέον, αναλύονται κάποιες βασικές έννοιες σχετικά με τις υπολειμματικές δομές, τα ασαφή σύνολα, την ασαφή λογική, τις ομάδες δικτυωτής διάταξης και τις MV-Άλγεβρες. Αυτές οι έννοιες είναι απαραίτητες για τα Ασαφή Δίκτυα Petri και κυρίως για την ανάπτυξη της λεγόμενης Petri Άλγεβρας. Τέλος αναλύονται κάποιες εφαρμογές των Ασαφών Δικτύων Petri. / This project is about Fuzzy Petri Nets. After a historical introduction in Petri Nets, we analyze the different types of Petri Nets as well as their properties. Furthermore, we focus on some basic concepts of the residuated structures, fuzzy sets, fuzzy logic, lattice-ordered abelian groups and MV-Algebras. These concepts are essential for Fuzzy Petri Nets and Petri Algebras. Finally, we analyze some basic applications of Fuzzy Petri Nets.

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The Geodetic network of Lesotho as established by the Directorate of Overseas Surveys in the 1950's, has been known to have distortions of several meters in some areas. This network is still very much in use today. Several altcmpts were made to strengthen the DOS network. but these attempts were not used for a complete readjustment. The South African Control net, which completely surrounds Lesotho, has recently been readjusted so as to bring it into sympathy with the WGS reference system used by GPS. It has become urgent to similarly update the Lesotho control system, to enable economical use of GPS surveying methods. This thesis addresses the problems of updating the Lesotho control system and also of bringing existing data onto the updated systcm. This thesis first reviews the historical background of Lcsotho and that of its geodetic net work. Different sets of data were collected and common points in the compared sets selected for the analysis. The South African readjustment was chosen as the standard, because it is the most recent, derived with the support of the new zero-order South African control net. The data sets were fitted to the reference system using conformal transformations from first up to fourth order. These comparisons were used to detect outliers. They revealed systematic distortions in the older data. which could be largely eliminated in the fourth-order transformation. The opportunity to update control point co-ordinates also gave an opportunity to revisit the existing choice of using two map panels of the Gauss Conform projection. The distortions involved in using a single Gauss Conform panel and also the UTM projection were investigated. A companson or all the methods and the recommendations concludes the section. Software was developed for transforming existing survey data onto the recommended updated reference system. The height system used in Lesotho is also reviewed because it forms part of the control net. The focus is on heights in relation to gravity. because that bears on the relation of published orthometric heights. with GPS-derived ellipsoidal heights. This section is mostly a literature review, starting with the theory of heights and gravity, proceeding onto the applied corrections and then showing what relations have been found. / Thesis (M.Sc.Sur.)-University of Natal, Durban, 2001.

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This work is dedicated to the making and research of mobile information system. Following tasks were completed in order to tackle this problem: mobile information system processes analysis; uml modeling analysis; formal modeling methods analysis; composition of system model; system model verification.

El objetivo de la tesis es la definición de un modelo de ejecución paralelo, que basado en la representación de un algoritmo paralelo con Redes de Petri, permita a un conjunto flexible de procesadores independientes entre sí, ejecutar el algoritmo en forma asíncrona con altos rendimientos y que el programador tenga capacidad de ajustar los parámetros de ejecución en vista de mejoras de rendimiento. Los fundamentos son claros: se desea contar con una herramienta de ejecución de programas paralelos que permita modelar el algoritmo, y pasar del modelo a la ejecución asíncrona preservando el modelo. Las Redes de Petri son la herramienta básica e indiscutiblemente pertinente para lograr el objetivo. Un desafío es cubrir la brecha o gap existente entre el modelado y una ejecución del programa paralelo de rendimientos aceptables y escalables.Para ello, debe existir una vinculación del modelo con un conjunto de unidades de procesamiento que corran en paralelo.

Las redes Peer-to-Peer (P2P) puras no estructuradas como Gnutella, dónde los nodos se conectan entre sí como pares o iguales, sin roles diferenciados ni jerarquías de ninguna clase, son sistemas distribuidos, dinámicos, sin punto alguno de centralización, que favorecen la robustez y tolerancia a fallos. Sin embargo, la búsqueda de recursos en estos sistemas constituye un problema esencial. El algoritmo de búsqueda BFS de Gnutella genera gran cantidad de tráfico dificultando su escalabilidad. Esta tesis propone un nuevo algoritmo de búsqueda denominado Búsqueda Inteligente Incremental P2P (BII-P2P) en el que los nodos, asistidos por sus redes neuronales locales, propagan selectivamente las solicitudes de búsquedas sólo al subconjunto más apropiado de vecinos. Así se mejora significativamente el algoritmo de Gnutella consiguiendo mayor porcentaje de hallazgos con menor cantidad de tráfico generado sobre la red P2P. El rendimiento de este algoritmo de búsqueda inteligente se ve potenciado por una conveniente estrategia de exploración incremental.

Petri nets are used as models in the study of networks involving information flows. Petri nets have also turned out to be useful in the study of many asynchronous concurrent systems.In this thesis, the notions of deadlocks, traps, and liveness are considered from a graph theoretic viewpointA characterization of minimal deadlocks and traps in Petri nets is obtained. For the complete Petri nets, alternative characterizations of deadlocks and traps are obtained. Necessary and sufficient conditions are obtained for complete Petri nets to be deadlock free. Similar conditions for trap free complete Petri nets are also determined. / Department of Computer Science