控制系统的飞程序及防飞技术

文中论述了二种防飞的技术,一种是有效看门技术,一种是秒复位技术。并提出如何克服飞程序引起的栈区变化等问题。     

MPLS VPN技术的研究

多协议标记交换技术(MPLS)是一种新出现的技术,旨在解决当前互联网环境中使用IP分组转发技术的许多问题。论文就基于IP的VPN技术在流量工程方面存在的问题,提出了基于MPLS技术的解决方案,并给出了一种基于MPLS的VPN流量管理模型。     

网络安全与防火墙技术研究

随着Internet的迅速发展,网络安全问题日益严重。解决网络安全问题的重要手段就是防火墙技术。对防火墙技术的基本概念和系统结构进行简单的介绍,讨论了实现防火墙的两种主要技术手段:一种是基于分组过滤技术(Packet filtering);一种是基于代理技术(Proxy)。最后对防火墙的未来发展趋势进行了简单的介绍。     

技术的选择是一个问题

在日前与同行的交流中谈到一个问题,现在的自动化技术门类越来越丰富,用户几乎都能够找到适合自己的一种解决方案,但是选择项的增多带来的是如何聪明决策的问题。换句话说就是,技术不是问题,问题是如何选择。以传统的PLC和DCS技术为例,首先,近年来计算机微处理器技术的迅速发展导致两种技术出现了融合的趋势,从表面上大家确实不难发现,两种技术的系统     

子旅行商问题及其蚁群求解算法

扩展旅行商问题是根据实际需要对传统旅行商问题的一种延伸和拓展,在实际问题中有许多有趣的应用。提出一种新的扩展旅行商问题(子旅行商问题),传统旅行商问题仅仅是子旅行商问题的一种特例。然后根据子旅行商问题的定义对蚁群系统算法进行改造,设计了一种有效的求解子旅行商问题的蚁群算法,并根据子旅行商问题的特点设计了一种高效的邻域局部搜索技术来提高解的质量。最后在10个TSPLIB范例上进行比较实验。结果表明:改进的蚁群算法能够有效求解提出的子旅行商问题,设计的邻域局部搜索技术是有效的。     

RFID中的反碰撞技术

标签碰撞是RFID系统中最常见、最难处理的问题,常用反碰撞技术来解决。根据ISO／IEC14443标准,反碰撞技术可分为面向比特和面向时隙两种,给出了每一种技术的冲突检测方法,并详细阐述了每一种技术的工作原理。     

流程工业CIMS中综合优化问题的研究

文章首先提出了流程工业及其ＣＩＭＳ中的各种优化问题,小结了各种解决优化问题的求解技术。在此基础上提出了一种基于多级优化的一种流程工业ＣＩＭＳ结构。最后,作者提出了一种解决流程工业ＣＩＭＳ多目标优化问题的最大熵优化技术。     

换个角度看技术

每个学科的教师都有自己的学科背景,也都习惯从自己学科的角度出发看问题,这几乎成为一种固定的思维方式。它不易察觉,因为它已经成了你骨子里的东西。就以信息技术教师为例,天然的就带有一种"技术思维",他们以技术为骄傲,甚至视技术为信仰。看问题自然从技术角度出发,其典型特征包括遇到问题首先想到用技术去解决,坚信技术的解决方案是最佳的……     

移动代理系统的安全框架

移动代理技术是一种新型的分布式网络计算模式,它很好地解决了网络间任务分配合作的问题,但是移动代理技术存在的安全问题限制了它的应用。该文为移动代理技术设计了一套安全框架,旨在解决移动代理技术中的安全认证及安全通信问题。     

Vmware虚拟机软件在网络技术实验中的应用

虚拟机技术应用于网络技术实验不仅是一种趋势,同时也是高校利用现有实验室有限计算机资源进行网络实验的一种捷径,文章讨论了虚拟机软件在网络技术实验中的注意事项和常见问题。     

Bridging objects and relations: a mediator for an OO front-end to RDBMSs

An object-oriented paradigm is established as the leading approach for developing non-traditional applications, such as GIS or multimedia systems. On the other hand, relational databases have dominated the area of data processing in the past decade. These two trends motivate the research on integrating OO applications with relational databases. This paper presents our approach to the symbiosis of the OO and relational data models, which is built into GinisNT, a scalable OO GIS framework based on an OO-to-relational mapping algorithm. The mapping algorithm transforms classes and objects into relations and tuples, and vice versa, instantiates objects from relational databases. The methodology presented here is extremely efficient, as has been proved by a number of applications developed in GinisNT, and is at the same time cost efficient, as it builds upon existing platforms.     

Performance evaluation of the object-relational transformation methodology

The emergence of the object-oriented (OO) methodology has shown its capabilities in modelling the real world better than the earlier relational methodology. However, object-oriented databases (OODBs) are still considered immature in comparison with relational databases (RDBs) which have existed for many years. RDBs still continue to dominate the implementation of databases constituting more than 90% of all database implementations [28]. It was felt worthwhile to exploit the great modelling power of OO methodology, while still facilitating relational implementations. These reasons have led us to develop an object-relational transformation methodology [20, 21, 22, 23, 24 and 25] which allows us to use the OO methodology for data modelling and to transform it into a relational logical model for implementation in relational database management systems (RDBMSs). The main purpose of this paper is to present a performance evaluation of the transformation methodology. The evaluation covers I/O cost models of different types of queries. The type of evaluation is basically comparison-based, in which the performance of SQL operations upon a set of tables derived from the relational data model is compared with the tables derived from the OO data model using the transformation methodology. The results of the evaluation show that the performance of the RDB implementation transferred from an OO conceptual model using our object-relational transformation methodology is better than the relational implementation using a conventional relational modelling. Moreover, in many cases, the relational modelling is not applicable since it cannot capture the design semantics particularly relating to collection types. Our object-relational methodology solves this problem.     

Query processing over object views of relational data

This paper presents an approach to object view management for relational databases. Such a view mechanism makes it possible for users to transparently work with data in a relational database as if it was stored in an object-oriented (OO) database. A query against the object view is translated to one or several queries against the relational database. The results of these queries are then processed to form an answer to the initial query. The approach is not restricted to a ‘pure’ object view mechanism for the relational data, since the object view can also store its own data and methods. Therefore it must be possible to process queries that combine local data residing in the object view with data retrieved from the relational database. We discuss the key issues when object views of relational databases are developed, namely: how to map relational structures to sub-type/supertype hierarchies in the view, how to represent relational database access in OO query plans, how to provide the concept of object identity in the view, how to handle the fact that the extension of types in the view depends on the state of the relational database, and how to process and optimize queries against the object view. The results are based on experiences from a running prototype implementation. Edited by: M.T. ?zsu. Received April 12, 1995 / Accepted April 22, 1996     

Implementing associations among classes in an environment of active databases

The association is a native concept from relational databases, one that has been adapted to object oriented (OO) modelling. It is an interesting operator used to describe links among objects of a system, commonly included in the most popular diagram-based OO methodologies. However, those methodologies sometimes present a lack of formality that may undermine its use. In this paper we formalize the semantics of associations. Firstly, we will describe an OO model based on different kinds of constraints. Some of them will be especially useful for describing the semantics of associations. Finally, we will present some remarks about implementation by means of triggers, a new feature incorporated in databases to specify an inner active behavior. This article was submitted by the authors in English.     

基于关系数据库的对象数据管理方法研究

面向对象方法在许多领域中已经得到了广泛应用 .对象描述方法可以很方便地描述领域中具有复杂结构的数据 ,但这些复杂数据的存储问题还有待妥善解决 .在数据存储管理方面 ,关系数据库系统一直处于主导地位 .本文提出了一种将对象模型和关系模型有机结合在一起的方法 .该方法将数据存储功能从领域数据对象中分离出来 ,采用专门的对象管理器来处理复杂的对象数据与关系数据库的交互问题 .该方法已经被用于海洋传播模型数据库管理系统的设计开发中 ,并取得较好的效果     

构造高性能的对象关系系统

面向对象技术是当今最流行的软件开发方法，关系模型是最常用的一种数据模型。结合这两种技术的优点，讨论了构造高性能对象关系系统的方法。     

Deriving Object Oriented Federated Databases and Processing Federated Queries

In this paper, we present a federated query processing approach to evaluate queries on an Object-Oriented (OO) federated database. This approach has been designed and implemented in the OO-Myriad project, which is an OO extension to the Myriad FDBS researchmyriad:94. Since data integration is performed as part of federated query processing, we have proposed outerjoin, outer-difference and generalized attribute derivation operations together with the traditional relational operations, to be used for integration purposes. To define an OO federated database as a virtual view on multiple OO export databases, we adopt a database mapping strategy that systematically derives each of the class extents, deep class extents and relationships of the federated database using an operator tree consisting of the integration operations. By augmenting federated database queries with this algebraic mapping information, query execution plans can be generated. Based on the original Myriad query processing framework, we have realized the proposed OO federated query processing approach in the OO-Myriad prototype.     

Managing the US Navy's first OO digital mapping project

In the late 1980s the Defense Mapping Agency began converting their paper maps into digital format. A military standard known as Vector Product Format emerged as the format for storing digital vector data. The VPF relational data model, however, has problems representing complex spatial data. In 1991, the US Navy, a DMA database user, began investigating how object technology could improve its digital maps. This research led to the development of the Object Vector Product Format, an object-oriented approach to viewing and editing digital maps and charts. By combining multiple relational databases into a single OO database, OVPF offers users such key advantages as the ability to immediately update and modify the content of the original data. Over the course of developing OVPF we have also learned some valuable lessons about managing OO projects. Our experiences have given us insight into some important risk-management techniques, including how to manage the expectations of decision-makers and sponsors and how to implement effective training methods. Managing the OVPF project was much more rewarding than most due to the greatly increased productivity offered by an OO approach     

Export database derivation in object-oriented wrappers

Wrappers export the schema and data of existing heterogeneous databases and support queries on them. In the context of cooperative information systems, we present a flexible approach to specify the derivation of object-oriented (OO) export databases from local relational databases. Our export database derivation consists of a set of extent derivation structures (EDS) which defines the extent and deep extent of export classes. Having well-defined semantics, the EDS can be readily used in transforming wrapper queries to local queries. Based on the EDS, we developed a wrapper query evaluation strategy which handles OO queries on the export databases. The strategy is unique in that it considers the limited query processing capabilities of local database systems as well as the language constraints on the local query languages.