Real-time transaction scheduling in database systems

A database system supporting a real-time application, which can be called “a real-time database system (RTDBS)”, has to provide real-time information to the executing transactions. Each RTDB transaction is associated with a timing constraint, usually in the form of a deadline. Efficient resource scheduling algorithms and concurrency control protocols are required to schedule the transactions so as to satisfy both timing constraints and data consistency requirements. In this paper,^† we concentrate on the concurrency control problem in RTDBSs. Our work has two basic goals: real-time performance evaluation of existing concurrency control approaches in RTDBSs, and proposing new concurrency control protocols with improved performance. One of the new protocols is locking-based, and it prevents the priority inversion problem^{, †} by scheduling the data lock requests based on prioritizing data items. The second new protocol extends the basic timestamp-ordering method by involving real-time priorities of transactions in the timestamp assignment procedure. Performance of the protocols is evaluated through simulations by using a detailed model of a single-site RTDBS. The relative performance of the protocols is examined as a function of transaction load, data contention (which is determined by a number of system parameters) and resource contention. The protocols are also tested under various real-time transaction processing environments. The performance of the proposed protocols appears to be good, especially under conditions of high transaction load and high data contention.     

Academic/industrial collaboration in a postgraduate MSc course in Software Engineering

This paper outlines the organization of an MSc in Software Engineering that has been set up as a specialist conversion course for graduates who have had some experience of computer programming. The most distinctive feature of the program is that this degree involves the participation of an industrial partner in providing some of the teaching and a period of industrial placement. Our experiences with the academic and practical aspects of such a structure have been included.^†     

Two individual computer workstations

This article describes two workstations to operate at under $10,000 and designed to provide the computer capabilities for a number of art- and design-related tasks. The article questions whether one computer graphic system and workstation is really suitable for all computer graphic tasks at least at the low and middle ranges of computer equipment and software.^† Implications for education in the arts are discussed and a range of options for the artist as well as the art educator are presented. Practical options and concerns for the purchase of computer hardware and software and video-related equipment are also discussed.     

Classification of paint on metallic surfaces using spatial domain analysis of laser images

In this paper a classification method is described for painted surfaces using laser image clarity meter (LIC)^†. In this method extracted features from reflected images of size (512 × 512 × 8 bits) from painted surfaces are used for classification purpose. The distance measured between the features of the test samples and the reference sample, which is smooth black glass, determines the deviation of the test sample from the reference. In comparing the result of 500 of the painted panels classified by the proposed method with the result of visual inspection, we have shown that this method is quite effective.     

Analysis of global pressure relaxation for flows with strong interaction and separation

A global or pressure relaxation formulation for the reduced form of the Navier-Stokes equations, frequently referred to as semi-elliptic or partially parabolized or just “parabolized” Navier-Stokes (PNS),^‡ is presented. Difference procedures and relaxation solutions for the (u, v, p) system are described. The continuity equation is satisfied exactly at each grid point and a poisson pressure equation is not required explicitly. Several model problems, e.g. finite flat plate, trough, boattail and airfoil, are considered. Strong pressure interaction is evident in each case and axial flow separation occurs for several of the problems. The questions of accuracy, stability, convergence rate, and implied difference forms of the pressure and vorticity equations are addressed. Solutions for laminar and turbulent modelling are presented.     

Touchscreen usage in plant computer systems: A case study

This paper describes one electric utility's implementation of touch technology on the operator interface of selected plant computer systems. Specifically described is the implementation of scanning infrared touch CRT's on the man/machine interface for the Plant Information Computer System (PICS) and the Performance Monitoring System (PMS). These systems utilize modular software packages developed by Southern Company Services, Inc. (SCSI),¹ Birmingham, Alabama. In addition, SCSI performs hardware integration, system installation, and startup. The systems described herein have been installed at various electric- generating units at Alabama Power Company.¹ The PICS system is a minicomputer-based system performing real-time data acquisition, graphic display, alarming, logging, performance calculations, and data base maintenance in an electric-generating plant environment. The PMS system is a microcomputer-based system performing similar functions as above, but emphasizing plant performance calculations and associated displays. This paper presents an overview of current touch technologies, describes the reasons why scanning infrared beam technology was chosen for use on the PICS and PMS systems, outlines the software methodology used in conjuction with touch input, and lists operator feedback and conclusions draw since system installation.     

Protocol performance measurements in a heterogeneous network environment

Reported are comparisons of TCP-, XTP¹- and UDP throughout measurements over an ATM inhouse network, the STM based part of the BERKOM^{, 2} B-ISDN and a CSMA/CD LAN. The impact of concurrent processes on the throughput performance was observed. XTP has been found to perform as well as and in some situations better than TCP/IP. Both XTP and TCP achieved about 8 Mb/s over Ethernet (ftp ˜ 8.7 Mb/s) and more than 17 Mb/s over a 140 Mb/s STM-channel of the BERKOM B-ISDN network (ftp up to 16 Mb/s). TCP/IP throughput performance on the basis of the latest Fore ATM system release available (SBA200 series) revealed a substantial increase in performance compared to previous releases of the Fore ATM network adapter. Experiments have shown that average throughput rates of up to 59 Mb/s are achievable with a SPARCstation 10 based ATM endsystem.     

Shaping user input: a strategy for natural language dialogue design

Traditional approaches to natural language dialogue interface design have adopted ordinary human-human conversation as the model for online human-computer interaction. The attempt to deal with all the subtleties of natural dialogues, such as topic focus, coherence, ellipsis, pronominal reference, etc. has resulted in prototype systems that are enormously complex and computationally expensive.

In a series of experiments^†, we explored ways of minimizing the processing burden of a dialogue system by channeling user input towards a more tractable, though still natural, form of Englishlanguage questions. Through linking a pair of terminals, we presented subjects with two different dialogue styles as a framework for online help in the domain of word-processing. The first dialogue style involved ordinary conversational format. The second style involved a simulation of an automated dialogue system, including apparent processing restrictions and ‘system process messages’ to inform the subject of the steps taken by the system during query analysis. In both cases human tutors played the role of the help system. After each dialogue session, subjects were interviewed to determine their assessments of the naturalness and usability of the dialogue interface.

We found that user input became more tractable to parsing and query analysis as the dialogue style became more formalized, yet the subjective assessment of naturalness and usability remained fairly constant. This suggests that techniques for channeling user input in a dialogue system may be effectively employed to reduce processing demands without compromising the benefits of a natural language interface. Theoretically, this data lends support to the hypothesis that unrestricted human-human conversation is not the most appropriate model for the design of human-computer dialogue interfaces.     

Iterative algorithm for a system of nonlinear variational-like inclusions

In this paper, we consider a system of nonlinear variational-like inclusions (SNVLI) in Hilbert spaces. In particular, SNVLI reduces to a variational inclusion, an extension of variational inclusion studied by ^{Hassouni and Moudafi [1]}. Using fixed-point method, we suggest an iterative algorithm for finding an approximate solution to SNVLI. Further, we prove the existence of solution and discuss convergence criteria for the approximate solution of SNVLI. The theorems presented in this paper improve and unify many known results of variational inclusions and variational inequalities, see for example ^{1., 2. and 3.}.     

Schedulability Criteria and Analysis for Dynamic and Flexible Resource Management

The Flexible Resource Manager (FRM) is a dynamic resource management approach that allows a better utilization of the available resources. However, it necessitates an atomic reconfiguration process that must not violate hard timing constraints. This paper exploits the deadline assignment rule of the Total Bandwidth Server (TBS) to schedule reconfiguration, and it formally shows that there exists a minimum task period for which atomicity and schedulability can be guaranteed. With this solution, real-time system engineers have the tools at hand to design their tasks to exploit the benefits of the FRM with hard real-time constraints.¹     

Application object model for engineering information systems

An object model for application development is introduced in the context of Engineering Information Systems (EIS)¹. The model shares features with several popular models and offers some less common ideas, such as operation-dependent state closure. The model is also unique in its position within the environment: it acts as a portability view independent of the underlying storage servers. The view-mapping is made most efficient however, if the object model of the underlying servers matches the structure of the EIS Application Object Model (AOM).     

Parameter identification for a class of abstract nonlinear parabolic distributed parameter systems

This paper studies the parameter identification problem of nonlinear abstract parabolic distributed parameter systems via variational method ^[1]. Based on the fundamental optimal control theory and the transposition method studied in ^[2], the existence of optimal parameter is proved, and the necessary condition for the optimal parameter is established.     

A cubic spline package. Part 1 — The user's guide

The computer-aided-design research group at Cambridge University Engineering Department wrote this spline package for use on the Atlas 2 computer at the CAD Centre, Cambridge. It has recently been implemented (by Dr Morris and Mr P. M. McLellan) for on-line users of ITT, and the examples in the text have been run on ITTS-RTS^*. A version also exists for IBM 1130 and 360/370 computers.

The heart of this set of programs is a spline subroutine of original construction which can handle any number of points without rounding-error difficulties, and which allows the user to permute the end conditions from a wide choice. The mathematical basis for this subroutine will be described in Part 2 of this paper.     

Knowledge-based information retrieval

A knowledge-based system is used as a front-end to a very large database to increase the relevance of the information being retrieved. The subject domain of the data base is modelled in a semantic network and the queries to the database are expanded according to the semantic model. An experiment has been performed on a bibliographic database, by developing the prototype KNOWIT, a knowledge-based front-end to the information retrieval system ESA-QUEST¹. An experimental evaluation shows that the number of relevant bibliographic references retrieved with the knowledge-based front-end is significantly improved, without compromising the precision of the retrieval.     

Datenbank-DIALOG: how to communicate with your database in German (and enjoy it)

The paper discusses the requirements for practical natural language interfaces (NLIs), claiming that acceptance is not only based on the linguistic capabilities of a system but on other features as well, particularly portability and ease of handling. It is shown how these features have been realised in Datenbank-DIALOG^*, a German language interface to relational databases. After a brief look at the linguistic capabilities of Datenbank-DIALOG we demonstrate our approach towards a portable and easy-to-handle system. We also show the dependability of the solutions on the design of the core system. The aspects mentioned have rarely been treated in the technical literature, furthermore it is their combination and interaction that makes Datanbank-DIALOG a suitable device for casual users of databases.     

A fully abstract model for the exchange of information in multi-agent systems

In this paper,¹ we present a semantic theory for the exchange of information in multi-agent systems. We consider the multi-agent programming language agent communication programming language, which integrates the paradigms of concurrent constraint programming and communicating sequential processes ( ). The constraint programming techniques are used to represent and process information, whereas the synchronous communication mechanism from is generalised to enable the exchange of information. The semantics of the language, which is based on a generalisation of traditional failure semantics, is shown to be fully abstract with respect to observing of each terminating computation its final global store of information.     

An alternative to expert systems for electrical diagnosis

Although the use of an expert system for the detection and location of faults in the power supply subsystem of the TDFI satellite¹ gives good practical results, there are also a certain number of drawbacks:

• - the rules are application-dependent and therefore useless for the diagnosis of other satellites,

• - the amount of knowledge required is quite large and contains a lot of redundant information,

• - testing and updating of the system are tricky,

• - it is far from sure that all possible faults can be taken into account.

The diagnosis theory based on models of correct behavior of the components introduced more recently by de Kleer and Williams seems more suited to this type of problem. Using our program CATS/DIANA, we have been able to validate this approach for analog electronic circuits. We have also tested the method on the diagnosis of satellite power supply subsystems; the results were similar to those obtained using an expert system, but without the drawbacks. This paper describes the two methods and compares the results.     

A strategic decision support system for supply network design and management in the semiconductor industry

This paper presents a strategic decision support system (DSS) which has been conceptualized and designed by SEMATECH^* to assist the large semiconductor manufacturing organization in managing its extensive supply chain network. This DSS has been named “Manufacturing Enterprise Model” or “MEM”. MEM ties each factory and its primary metrics to the rest of the business enterprise to assess how changes in wafer fabrication affect other factories, the distribution system, and customer deliveries. The model is intended to be used to evaluate future factory concepts and to assist business planners in strategic decisions about product allocation and major resource/facility planning.     

Optimum control of neutron flux during nuclear station load following

Pontryagin's Maximum Principle is utilized to determine the optimum control of nuclear reactor power during station load following. The optimal control equations are solved by means of a gradient method, time weighted steepest descent, combined with the clipping off technique for constrained control variables. The gradient method iterates directly on the control function. The two point boundary value problem is addressed by using both forward and backward time integration. A performance index which measures reactor operating cost, including the effect of reduced fuel burnup due to Xenon poisoning, is extremized. Results for a range of reactor material costs are presented for a CANDU^§ reactor.