Applying expert principles to computer systems development: Using compilers and generators

Expert systems can be used for developing computer systems. The expert system can help in expressing the definition of the problem, as well as answering the problem. So it deals with ‘how’ and ‘what’ in the development of a computer system. The two main approaches to providing solution expertise are to use a compiler or a generator. The generator approach is more limited than the compiler approach. The Systematics generator includes precoded design templates in its knowledge base. The two main approaches to problem statement are data-driven or goal-driven.     

Braess-like paradoxes in distributed computer systems

We consider optimal distributed decisions in distributed computer systems. We identify a Braess like paradox in which adding capacity to the system may degrade the performance of all users. Unlike the original Braess paradox, we show that this behavior occurs only in the case of finitely many users and not in the case of infinite number of users     

Using schedulers to test probabilistic distributed systems

Formal methods are one of the most important approaches to increasing the confidence in the correctness of software systems. A formal specification can be used as an oracle in testing since one can determine whether an observed behaviour is allowed by the specification. This is an important feature of formal testing: behaviours of the system observed in testing are compared with the specification and ideally this comparison is automated. In this paper we study a formal testing framework to deal with systems that interact with their environment at physically distributed interfaces, called ports, and where choices between different possibilities are probabilistically quantified. Building on previous work, we introduce two families of schedulers to resolve nondeterministic choices among different actions of the system. The first type of schedulers, which we call global schedulers, resolves nondeterministic choices by representing the environment as a single global scheduler. The second type, which we call localised schedulers, models the environment as a set of schedulers with there being one scheduler for each port. We formally define the application of schedulers to systems and provide and study different implementation relations in this setting.     

Using directed hypergraphs to verify rule-based expert systems

Rule-based representation techniques have become popular for storage and manipulation of domain knowledge in expert systems. It is important that systems using such a representation are verified for accuracy before implementation. In recent years, graphical techniques have been found to provide a good framework for the detection of errors that may appear in a rule base. The authors present a graphical representation scheme that: 1) captures complex dependencies across clauses in a rule base in a compact yet intuitively clear manner and 2) is easily automated to detect structural errors in a rigorous fashion. Their technique uses a directed hypergraph to accurately detect the different types of structural errors that appear in a rule base. The technique allows rules to be represented in a manner that clearly identifies complex dependencies across compound clauses. Subsequently, the verification procedure can detect errors in an accurate fashion by using simple operations on the adjacency matrix of the directed hypergraph. The technique is shown to have a computational complexity that is comparable to that of other graphical techniques. The graphical representation coupled with the associated matrix operations illustrate how directed hypergraphs are a very appropriate representation technique for the verification task     

Using visualization to maintain large computer systems

The Year 2000 software conversion effort dramatically illustrates how time consuming and costly maintaining large computer systems can become, especially when each system consists of millions of lines of source code. Understanding how a system's components interact is a key factor in implementing portfolio-wide changes, adding new features, and providing ongoing system maintenance. Any help that software developers can get in making existing software systems easier to understand improves developer productivity, enhances software quality, and reduces development cycles, all leading to faster time to market. The paper discusses the Visual Insights code viewer, a visualization application developed specifically to address the problem of working with large amounts of source code. Used within the Lucent Technologies 5ESS Switch development environment, the code viewer has resulted in increased software developer productivity. In addition, a systems integrator currently uses this tool to help understand and correct the Year 2000 date references in customer software     

On security measures in distributed computer systems

Problems of data security are becoming increasingly acute. This study of these basic problems has been carried out in cooperation between scientists at the Department of Electrical Engineering at Linköping Institute of Technology and FOA 3 (Försvarets Forskningsanstalt Planeringsbyrån — Research Institute of National Defense, Operations Research Center).The situation considered is an office with individual work stations having desktop computers. These communicate among themselves and share a host computer of higher capacity including special purpose input/output equipment.Among questions discussed are:

• * problems related to the protection of data bases

• * ease of selectively designating addressees and authorisation to access data and messages; key distribution and protection

• * general requirements for equipment needed in such a local net environment.

No attempt has been made to predict when such distributed office computer systems will become commonly available in full scale. It does, however, seem clear that they are at least technically feasible already.     

The design of distributed control computer systems

The top-down approach in the design of Distributed Control Computer Systems, DCCS, is presented. The starting point of the study is three statements: (i) the design approach should be production process control oriented; (ii) for real time process control applications, computer networks require an efficient communication subsystem, the most important features of which are high reliability and short message transmission times and (iii) recent research has shown that the tools and methodologies used in both computing and control should be complementary to each other in order to solve some of the distributed control computer system/distributed computer control system design problems. The paper contains the design problems of distributed control computer systems, the presentation of the methods and tools for the study and design of the DCCS, the top-down approach in the design of the DCCS, and examples of two design stages.     

Using statistics to make expert systems “user-acquainted”

The user-acquainted feature collects user-specific data regarding the types of advice that have been sought over time and uses this historical information to update the probabilities to affect the firing of its rules and the ordering of the recommendations of the expert system. These updates are done on auser-specific basis so that the expert can more closely emulate a true expert by providing more informed advice. One example of a place where evidence suggests that such a feature would be useful is in the area of debugging of computer programs, especially in support of novice programmers who tend, as individuals, to commit similar classes of errors over time, but who, as a group, commit very different types of errors. We conjecture that the user-acquainted feature, which can keep track of the tendencies of the users and take them into account in the evaluation of diagnostics, will be more effectiveand efficient in determining the fault. In this paper, we discuss the statistical analyses necessary to implement this feature in an expert system for debugging errors in SAS.     

Using execution trace data to improve distributed systems

One of the most challenging problems facing today's software engineer is to understand and modify distributed systems. One reason is that in actual use systems frequently behave differently than the developer intended. In order to cope with this challenge, we have developed a three‐step method to study the run‐time behavior of a distributed system. First, remote procedure calls are traced using CORBA interceptors. Next, the trace data is parsed to construct RPC call‐return sequences, and summary statistics are generated. Finally, a visualization tool is used to study the statistics and look for anomalous behavior. We have been using this method on a large distributed system (more than 500000 lines of code) with data collected during both system testing and operation at a customer's site. Despite the fact that the distributed system had been in operation for over three years, the method has uncovered system configuration and efficiency problems. Using these discoveries, the system support group has been able to improve product performance and their own product maintenance procedures. Copyright © 2002 John Wiley & Sons, Ltd.     

Using computer controlled physical models to analyze computer integrated manufacturing systems

It is usually difficult to design and install complex computer integrated manufacturing (CIM) systems without a large amount of time spent on debugging. In many cases miniature computer controlled physical models can provide information that reduces the time spent in the design and installation of larger systems. This paper describes how miniature physical models can be used to help industrial engineers design and install CIM systems.     

Assignment of availability objectives to components of heterogenous distributed computer systems

This paper provides a scheme to assign availability objectives to various components of a heterogenous distributed computer system using a minimum cost criteria. The availability is viewed from a user (client) perspective rather than the traditional system perspective. The user availability objectives are classified in terms of operational and inherent availabilities. Such a classification enables the designers to take into account the user expectations in a more realistic way thus minimizing the high cost of providing fault tolerant systems. The user availability objectives are then translated into the system availability objectives by relating the availability needs of each distinct user group to system components utilized by that group.     

Configuring distributed computer systems with online database backups

Designers of distributed computer systems face many complex decisions in determining the system configuration. These decisions involve location of computing resources, determination of databases and allocation of one or more copies of these databases among computing facilities. This paper deals with the configuration problem for a class of organizations that are critically dependent on the availability of their computer systems, and have widely dispersed operations with localized information needs. These organizations require online back-up copies of their databases in order to continue their operations in case of failure of a computer installation or a communication channel. An integer programming formulation of the problem is presented and an effective solution procedure is developed. Computational experience with this procedure is reported.     

Real-time task reallocation in fault-tolerant distributed computer systems

We address the issue of real-time task reallocation due to the failure of one or more processors in a software implemented fault-tolerant system. The incremental and total task reallocation problems are discussed, and a heuristic procedure for both problems is proposed. Computational experiments with the heuristic on the total task reallocation problem produce near perfect system reconfigurations. Further experiments with a slightly modified version of the heuristic show that excellent quality system reconfigurations are obtainable with minimal computational effort.     

A software architecture for distributed computer control systems

Distributed computer control systems have a number of potential advantages over centralized systems, especially where the application is itself physically distributed. A computer station can be placed close to the plant being controlled, and a communications network used to enable the stations to communicate to coordinate their actions. However, the software must be carefully designed to exploit the potential advantages of distribution. This paper describes the software architecture of CONIC, a system to support distributed computer control applications. This architecture emphasizes the distinction between the writing of individual software components and the construction and configuration of a system from a set of components. A modular structure is used to separate programming from configuration. Typed entry and exit ports are used to clearly define module interfaces. Ports, analagous to the plugs and sockets of hardware components, permit modules to be interconnected in different ways. On-line modification and extension of the system is supported by permitting the dynamic creation and interconnection of modules. Message passing primitives are provided to permit modules to coordinate and synchronize control actions.     

The internet-based knowledge acquisition and management method to construct large-scale distributed medical expert systems

The Internet offers an unprecedented opportunity to construct powerful large-scale medical expert systems (MES). In these systems, a cost-effective medical knowledge acquisition (KA) and management scheme is highly desirable to handle the large quantities of, often conflicting, medical information collected from medical experts in different medical fields and from different geographical regions. In this paper, we demonstrate that a medical KA/management system can be built upon a three-tier distributed client/server architecture. The knowledge in the system is stored/managed in three knowledge bases. The maturity of the medical know-how controls the knowledge flow through these knowledge bases. In addition, to facilitate the knowledge representation and application in these knowledge bases as well as information retrieval across the Internet, an 8-digit numeric coding scheme with a weight value system is proposed. At present, a medical KA and management system based on the proposed method is being tested in clinics. Current results have showed that the method is a viable solution to construct, modify, and expand a distributed MES through the Internet.     

Verification of concurrent control flow in distributed computer systems

An approach to verifying control flow in distributed computer systems (DCS) is presented. The approach is based on control flow checking among software components distributed over processors and cooperating among them. In this approach, control-flow behavior of DCS software is modeled and contained in special software components called verifiers. The verifiers are distributed over the processors and consulted to check the correctness of the control flow in DCS software during its execution. Algorithms for deriving the verifiers are presented. This technique can detect global errors including synchronization errors as well as local errors. It can be used for sequential or concurrent software at various levels of details. Experiments show that using this technique requires no significant overhead.<>     

Standby redundancy: Crash-tolerant computers for distributed computer systems

Distributed systems allow greater overall availability. Standby redundancy can be incorporated into application software to improve availability in the event of a crash. The Tandem-16 is an example of crash-tolerant computers. Other examples include Prosur, intended for a hostile environment, and Demos M/P, which uses a broadcast network and a computer called the ‘recorder’. Local area networks can introduce greater vulnerability.     

Using computer conferencing and case studies to enable collaboration between expert and novice teachers

Abstract This paper reports on a teaching innovation where groups of experienced and novice teachers collaborated in analyzing case studies involving the education of students with special learning needs. The teachers collaborated in an asynchronous computer conferencing system (Web Knowledge Forum). All participants were enrolled in special education graduate courses taught by the authors. The authors discuss the use of case studies in teacher education, collaboration between novice and expert teachers, and highlight some of the demands of computer conferencing particularly in relation to the loss of face-to-face interactions and the interpretive demands of electronic communication.