A Free Form Feature Taxonomy

In this paper the notion of free form feature for aesthetic design is presented. The design of industrial products constituted by free form surfaces is done by using CAD systems representing curves and surfaces by means of NURBS functions, which are usually defined by low level entities that are not intuitive and require some knowledge of the mathematical language. Similarly to the feature-based approach adopted by CAD systems for classical mechanical design, a set of high level modelling entities which provides commonly performed shape modifications has been identified. Particularly, the paper suggests a classification of the so-called detail features for an aesthetic and/or functional characterization of predefined free form surfaces. Feature types are formally described by means of an analytical definition of the surface modification through deformation and elimination laws. A topological classification is then given according to the application domain of such laws. A further sub-classification of morphological types is then suggested according to geometric properties of weak convexity and concavity for the resulting modified shape, leading to a taxonomy of simple free form features meaningful for aesthetic design.     

A Synthetic Workload Generation Technique for Stress Testing Session-Based Systems

Enterprise applications are often business critical but lack effective synthetic workload generation techniques to evaluate performance. These workloads are characterized by sessions of interdependent requests that often cause and exploit dynamically generated responses. Interrequest dependencies must be reflected in synthetic workloads for these systems to exercise application functions correctly. This poses significant challenges for automating the construction of representative synthetic workloads and manipulating workload characteristics for sensitivity analyses. This paper presents a technique to overcome these problems. Given request logs for a system under study, the technique automatically creates a synthetic workload that has specified characteristics and maintains the correct interrequest dependencies. The technique is demonstrated through a case study involving a TPC-W e-commerce system. Results show that incorrect performance results can be obtained by neglecting interrequest dependencies, thereby highlighting the value of our technique. The study also exploits our technique to investigate the impact of several workload characteristics on system performance. Results establish that high variability in the distributions of session length, session idle times, and request service times can cause increased contention among sessions, leading to poor system responsiveness. To the best of our knowledge, these are the first results of this kind for a session-based system. We believe our technique is of value for studies where fine control over workload is essential     

Special Feature: Fillin: A Reusable Tool for Form-Oriented Software

The reusable tool was designed to improve man-machine interaction. Its tool-oriented environment also enforces standards better than any list of rules can.     

Special Feature Computer Graphics: A Two-Way Street

We design-in the characteristics of the computer graphics system; those of the human visual system—at the other end of the street—are equally important.     

The Effect of Workload and Workshift on Air Traffic Control: A Taxonomy of Communicative Problems

Communication is crucial for air navigation safety: communicative problems are implied in 70% of aviation accidents and incidents. This study investigated the influence of workshift (backward rapid rotation) and workload on air traffic controller (ATCo) communications: a taxonomy of possible communicative errors and incorrectness was designed and a specific grid proposed to analyse the communicative exchanges taking place during the workshifts and under different workloads. The corpus we used to design and test our taxonomy and obtain measures of the communicative performance of ATCos consisted of 10 hours of radio exchanges between tower and approach controllers and pilots in an Italian airport. Results showed that the taxonomy was indeed apt to capture a variety of communicative problems: controllers widely employed a linguistic code strongly deviating from standard phraseology, with a widespread presence of Italian language, of non-standard expressions, ellipses and redundancies. Shiftwork and workload significantly affected the ATCos’ communicative performance: linguistic deviations significantly increased during the nightshift with a low workload, while the most correct exchanges occurred in the morning shift. Correspondence and offprint requests to: Cristina Cacciari, Department of Biomedical Sciences, Via Campi 287, 41100 Modena, Italy. Email: cacciari.cristina@unimo.it     

Special Feature: Software Maintainability: A Practical Concern for Life-Cycle Costs

Software modifiability doesn't just happen. It must be designed, tested, and paid for just like any other software requirement.     

Special Feature: Monitoring Program Execution: A Survey

Progress in this realm of performance measurement has lagged behind advances in the general field of programming languages: careful study of its capabilities and limitations is long overdue.     

Special Feature: Software Theft

Modular decomposition offers a way to ascertain a software theft. Morevoer, the method is straightforward enough for a software-illiterate judge or jury to understand     

Special Feature: Memory Extension Techniques for Minicomputers

There are many computer users these days who have bumped up against the end of their memories. Years ago, IBM 1800, 1130, and 7094 users discovered that 32K words of addressable memory simply was not enough. Today, minicomputer users are discovering the same thing. And so are minicomputer manufacturers. Some of the newest mini's can address 128K, 256K, 512K, or even 1024K (1M) bytes of main memory. The claim is that 16M byte addressing is right around the corner.     

Special Feature: Structures for Advanced Information Systems

More effective means for processing and communicating information are now at hand. However, certain problems must be solved to achieve satisfactory structures for integrated information systems.     

Special Feature Zork: A Computerized Fantasy Simulation Game

Is magic real? Do swords glow if the enemy is nearby? In the demonic world of Zork, a simulated universe entices the player into a new form of problem solving.     

基于特征点的特定人脸三维网格的生成

提出了一种在通用人脸模型的基础上,依据特定人脸正面图象和侧面图象得到特定人脸的三维网格模型的方法。该方法首先从特定人脸正面和侧面图象上提取特征点,然后依据这些特征点信息对相应人脸网格模型进行特征点变换,在此基础上对其余非特征点使用插值变换,从而将特定人的特征信息溶入到通用人脸模型中去,由此得到特定人脸的三维网格模型。通过试验取得了一定的效果。     

一种时序电路的测试生成算法

本文提出了一种高效的时序电路测试生成算法,该算法是建立在自适应算法的基础上,并使用了十七值逻辑模型。文章详细介绍了该测试算法的内容及其实现过程,并举例说明了该算法的测试效率。     

Hitest: A Knowledge-Based Test Generation System

Efforts to develop computer-based automatic test generation for digital circuits have been generally unsuccessful, except in the case of combinational circuitry. Current ATPG methods for sequential circuits often require a considerable amount of computer time and generate unstructured test waveforms of limited value. Experienced human test programmers, on the other hand, appear to have little difficulty in generating high-quality tests for complex sequential circuits when they have a good understanding of how the circuit operates. This article considers the causes of failure in automatic test generation algorithms and describes a new system called Hitest. This system lets the computer use human understanding of circuit operations to generate more effective tests.     

Special Feature: Interactive Graphics Teleconferencing

Interactive graphic displays of layouts or design plans, already in widespread use as design aids, can be even more effective when used in conjunction with teleconferencing.     

Special Feature: An Architecture for Real-Time Software Systems

The Rex approach to software architecture views executives as independently programmable machines that execute conventional-language application procedures as individual instructions of a higher-level program.     

Special Feature: Microprogrammable Virtual Machines

The introduction of computers which have user alterable microprograms presents users with both an opportunity and a problem. To take full advantage of the opportunity to tailor the architecture of the computer to the application domain, the problem of microprogram development and testing must be solved. The technique outlined here provides a tool which furnishes the microprogrammer with a virtual machine which is microprogrammable. The function provided is similar to that provided by a simulator, but the technique is more efficient and allows multiple microprograms to be executed concurrently with regular programs on a single real machine.     

Special Feature: Commercial Multiprocessing Systems

Multiprocessing has distinct advantages–and unique constraints with implications for performance. This survey highlights the architectural strategies of five multiprocessor systems.