Libero Nigro

Using Real Time Constraints for Modularisation

This paper advocates an object-oriented approach to the development of distributed real-time systems which clearly separates timing from functional concerns. It also describes a philosophy for modularising, and then designing systems, based on the localisation of timing constraints as one of prime criteria for partitioning. Active objects (i.e., actors) are adopted as the basic building blocks in-the-small. They are not aware of timing constraints nor of scheduling structures. Active objects are in charge of processing messages as they arrive. Message buffering and delivery is the responsibility of a control machine which hosts a reflective scheduler object. Timing constraints express, in general, patterns of multi-object, time-driven co-ordination and synchronisation. The resultant approach improves modularity and object reusability. The paper illustrates the application of the proposed concepts through real world examples.

Timing as a programming-in-the-large issue

Abstract HyperReal is an object-based programming paradigm which introduces a time-driven control model as a primitive mechanism. A system consists of a collection of actors which are not aware of timing issues. Timing is specified at a programming-in-the-large level, thus improving modularity and re-usability. The paper discusses the rationale for this approach; introduces HR2, an Oberon-based subset of HyperReal; and presents a set of examples which highlight how HR2 can be used for supporting different control disciplines.

Integrating the user interface in an object-oriented measurement system

The aim of this work is to apply the object-oriented (OO) programming technology to the development of computer-based measurement systems. The chosen framework is centred on a concurrent, time-sensitive, OO programming model, which in general is suited to the construction of real-time applications. The paper first highlights basic methodological issues of the proposed model and its usefulness in the construction of the software of an automatic measurement system. Then it concentrates on a possible realization of the user interface which strictly adheres to the OO paradigm and fits naturally into the adopted model. A careful layering of the architecture together with a proper use of the inheritance mechanism allow to reuse pre-defined user interface objects whose external behaviour is specialized for each test method. The use of the graphical interface is exemplified by means of some measurement examples.

Performance of a Time Warp based simulator of large scale PCS networks

Abstract This paper describes an object-oriented Time Warp (TW) mechanism which supports general parallel simulation on a distributed, possibly heterogeneous, computing environment. As a significant application of the developed TW, a simulation model adequate for large personal communication services (PCS) networks is proposed and its performance results given. Special attention is paid to such TW critical issues as load balancing and checkpointing interval tuning which strongly affect the achievement of good speedups. The experimental results confirm that good performance can be obtained on an heterogeneous distributed system provided an accurate parameter tuning is accomplished.

Modeling and Analysing DART Systems Through High-Level Petri Nets

The work described in this paper is concerned with modeling and analysing distributed object-oriented real time (RT) systems, developed according to DART — Distributed Architecture for Real Time — which provides an object-oriented life cycle for RT systems. The paper first gives an overview of DART, then discusses the usefulness of mapping DART systems onto high level Petri nets as part of an iterative design process. The resultant framework is a modular operational model, based on a powerful Petri nets tool which delivers both the user-interface utilised for animation purposes and a set of mechanisms suited for the analysis of time-dependent behaviour.

On the type extensions of Oberon-2

Oberon-2, the latest Prof. N. Wirth language design, supports object - oriented (OO) programming through an original record type extension mechanism. The language is expected to gain a growing acceptance both in the academic and industrial worlds. This short note aims to make a critical evaluation of Oberon-200 facilities by showing how the current language definition can be too restrictive in the building of usual type hierarchies like those allowed, for instance, by C++. A minor extension is suggested which improves the effectiveness of Oberon-2.