Monitoring and analysis of queries in distributed databases

Dissertação de Mestrado em Engenharia Informática

A survey of distributed data aggregation algorithms

Distributed data aggregation is an important task, allowing the de- centralized determination of meaningful global properties, that can then be used to direct the execution of other applications. The resulting val- ues result from the distributed computation of functions like count, sum and average. Some application examples can found to determine the network size, total storage capacity, average load, majorities and many others. In the last decade, many di erent approaches have been pro- posed, with di erent trade-o s in terms of accuracy, reliability, message and time complexity. Due to the considerable amount and variety of ag- gregation algorithms, it can be di cult and time consuming to determine which techniques will be more appropriate to use in speci c settings, jus- tifying the existence of a survey to aid in this task. This work reviews the state of the art on distributed data aggregation algorithms, providing three main contributions. First, it formally de nes the concept of aggrega- tion, characterizing the di erent types of aggregation functions. Second, it succinctly describes the main aggregation techniques, organizing them in a taxonomy. Finally, it provides some guidelines toward the selection and use of the most relevant techniques, summarizing their principal characteristics.

An object-oriented model for rapid prototyping of data path/control systems - a case study

Publicado em "Information control in manufacturing 1998 : (INCOM'98) : advances in industrial engineering : a proceedings volume from the 9th IFAC Symposium, Nancy-Metz, France, 24-26 June 1998. Vol. 2"

Object-oriented inheritance of statecharts for control applications

This paper discusses how object-oriented iuheritance can be re-interpreted if statecharts are used for modelling the dynamic behaviour of an object. The support of inheritance of statecharts allows the improvement of systems' development by easing the reutilization of parts of already developed euccessful systems, aad by promoting the iterative and continuous models' refinement advocated by the operatioaal approach. Statechart is the formalism used within UML to specify reactive state.based behaviours. This paper covers the use of statecharts within the modelling of embedded systems for industrial control applxications, where performance and memory usage are main concerns.