Petri net based process scheduling: A model of the control system of flexible manufacturing systems

In this paper, we propose a class of algorithms for the sub-optimal solution of a particular class of problems of process scheduling, particularly focusing on a case study in the area of flexible manufacturing systems (FMSs). The general class of problems we face in our approach is characterized as follows: there is a set of concurrent processes, each formed by a number of temporally related tasks (segments). Tasks are executable by alternate resource sets, different both in performance and costs. Processes and tasks are characterized by release times, due dates, and deadlines. Time constraints are also present in the availability of each resource in resource sets. It has been proven that such a problem does not admit an algorithm for an optimal solution in polynomial time. Our proposed algorithm finds a sub-optimal schedule according to a set of optimization criteria, based on task and process times (earliness, tardiness), and/or time independent costs of resources. Our approach to process scheduling is based on Timed Coloured Petri Nets. We describe the structure of the coordination and scheduling algorithms, concentrating on (i) the general-purpose component, and (ii) the application-dependent component. In particular, the paper focuses on the following issues: (i) theautomatic synthesis of Petri net models of the coordination subsystem, starting from the problem knowledge base; (ii) the dynamic behavior of the coordination subsystem, whose kernel is a High Level Petri net executor, a coordination process based on an original, general purpose algorithm; (iii) the structure of the real-time scheduling subsystem, based on particular heuristic sub-optimal multi-criteria algorithms. Furthermore, the paper defines the interaction mechanisms between the coordination and scheduling subsystems. Our approach clearly distinguishes the mechanism of the net execution from the decision support system. Two conceptually distinct levels, which correspond to two different, interacting implementation modules in the prototype CASE tool, have been defined: theexecutor and thescheduler levels. One of the outstanding differences between these levels is that the executor is conceived as a fast, efficient coordination process, without special-purpose problem-solving capabilities in case of conflicts. The scheduler, on the other hand, is the adaptive, distributed component, whose behavior may heavily depend on the problem class. If the scheduler fails, the executor is, in any case, able to proceed with a general-purpose conflict resolution strategy. Experimental results on the real-time performance of the kernel of the implemented system are finally shown in the paper. The approach described in this paper is at the basis of a joint project with industrial partners for the development of a CASE tool for the simulation of blast furnaces.     

Genetic algorithms for optimal logical database design

The focus of this paper is database design using automated database design tools or more general CASE tools. We present a genetic algorithm for the optimization of (internal) database structures, using a multi-criterion objective function. This function expresses conflicting objectives, reflecting the well-known time/space trade-off. This paper shows how the solution space of the algorithm can be set up in the form of tree structures (forests), and how these are encoded by a simple integer assignation. Genetic operators (database transformations) defined in terms of this encoding behave as if they manipulate tree structures. Some basic experimental results produced by a research prototype are presented.     

开发冲模CAD/CAM系统新模式的研究

基于ＣＡＳＥ（ＣｏｍｐｕｔｅｒＡｉｄｅｄＳｏｆｔｗａｒｅＥｎｇｉｎｅｅｒｉｎｇ）技术原理和冲摸设计与制造过程的特点以及ＣＡＤ／ＣＡＭ技术原理，在文献［２］的研究基础上，提出并研制了一种面向最终用户能多快好省地开发具体冲模ＣＡＤ／ＣＡＭ系统的新模式：冲模ＣＡＤ／ＣＡＭ系统的集成开发平台，论述了平台的总体设计思想，体系结构和工作流程，并给出实现平台的关键技术问题     

Oracle/CASE在建设项目投资控制系统开发中的应用分析

ＣＡＳＥ是计算机辅助技术应用于软件工程的结果,是目前信息系统设计开发集成环境与工具研究的热点和发展方向。结合信息系统设计和开发的实践,在建设项目投资控制系统设计开发中对Ｏｒａｃｌｅ／ＣＡＳＥ的应用进行了分析和探讨,主要对系统设计开发中的开发策略,基本设计过程和对Ｏｒａｃｌｅ／ＣＡＳＥ的核心数据字典等关键问题进行了分析。     

一个支持OO协同式设计的CASE工具

这篇文件介绍一个计算机辅助协同面向对象设计系统的设计与实现技术。文中所述的系统全面支持ＯＯＤ辅助设计,它实现了对象式系统中的要素表示及可视化设计,并支持多用户的协同开发。     

基于服务连接和消息连接软件构架的研究

软件构架是解决复杂大型软件开发面临的困难，提高软件质量和软件生产效率的有效方法，是软件复用和基于构件软件工程研究的重要领域，通过对软件构架风格特点的讨论和对构件之间交互方式的分析，论文提出了基于服务连接和消息连接的软件构架风格，开发了一个支持该构架风格的构件生产和组装平台，该构架风格具有以下特点，（1）支持多种可变性机制；（2）构件之间灵活和显式的服务连接和消息连接机制；（3）支持构件合成；（4）构件接口分组，成为端口。     

办公事务对象动态管理和统计分析系统及其应用

“办公事务对象动态管理和统计分析系统”的设计目标是解决一类“办公事务管理对象”的动态管理问题，因此实际上它是一个软件开发的工具。本文阐述了它的设计思想和功能结构，以及如何利用它来开发一个“纪检监察案件动态管理和统计分析系统”。     

在CASE工具中引入XML视图

从数据库设计的角度出发，在CASE(计算机辅助系统工程)工具中添加了创建XML视图的功能，也就是说在使用CASE对实体及其相互联系建模之后，在创建数据库对象的DDL语句的同时自动的创建此数据库的XML视图．具体的方法是将E-R模型转换为DTD来完成了这个数据库的XML视图的创建，一次性的完成了数据库的设计和此数据库的XML视图的创建，从而避免了程序员为了生成视图而对此数据库进行的二次开发，因此提高了工作效率．     

Matter Timed

At best, the ageing of materials is regarded as lending a patina to historic buildings. In reality, however, materials often age disgracefully and unevenly, requiring a high level of maintenance and refurbishment. What if materials could be engineered and integrated into buildings not only to enhance but to heal? Martina Decker , Assistant Professor in the College of Architecture and Design at the New Jersey Institute of Technology (NJIT), looks at pioneering research that is being undertaken into performative, time-dependent materials.     

TYIN tegnestue Architects. Integrating On-Site Education and Practice

Founded by Andreas Grøntvedt Gjertsen and Yashar Hanstad, TYIN tegnestue Architects grew out of an initiative to provide sleeping accommodation for an orphanage in Thailand when the principals were only third-year architecture students. Norwegian architect Lisbet Harboe explains how the student-architects built up a practice while in schools by refocusing their studies and those of their peers on learning through their own experiences of construction.