Software fault tree analysis

With the increased use of software in safety critical systems, software safety has become an important factor in system quality. This paper describes a technique, software fault tree analysis, for the safety analysis of software. The technique interfaces with hardware fault tree analysis to allow the safety of the entire system to be maximized. Experience with the technique and its practicality are discussed.     

A methodology to model the information structure of an organization

The Integrated Computer Aided Manufacturing (ICAM) program of the U.S. Air Force identified a need to better communicate and analyze manufacturing for the people involved in improving productivity. To satisfy that need, the ICAM program developed the IDEF (ICAM Definition) method to address particular characteristics of manufacturing. This IDEF method is equally applicable in analyzing other types of organizations. IDEF comprises three modeling methodologies: function model methodology (IDEF₀), information model methodology (IDEF₁) and dynamics model methodology (IDEF₂). This paper reports on the Information model methodology only. This methodology is used to construct an information model that helps in understanding the structure of information needed to support the functions of an organization.     

The external structure: Experience with an automated module interconnection language

To study the problems of modifiable software, the Software Technology project has investigated approaches and methodologies that could improve modifiability. To test our approaches tools based on data abstraction—a design and programming language and a module interconnection language—were built and used. The incorporation of the module interconnection language into design altered the traditional model of system building. Introducing novices to our approach led to the formalization of new models of program design, development, and evaluation.     

Modeling and projection in software development

Modeling is a fundamental technique for coping with undesirable complexity in constructing and reasoning about software systems. The concept of modeling can be applied to software design and implementation in two ways: a design can be viewed as an abstract model of the system it represents, and designs and implementations may be represented by even more abstract, simplified models for purposes of analysis. A discussion of these concepts and their applications is presented, including a case study showing the use of modeling in the debugging of an actual software system and remarks on research in progress.     

An analysis of program execution on a recursive stream-oriented data flow architecture

The functional or applicative approach to the development of software leads to the natural exposure of parallelism. Data flow architectures are designed to exploit this parallelism. This paper describes a method for modeling and analyzing program execution on a stream-oriented, recursive data flow architecture. Based on a maximum path length technique, a recursive analysis of nodes (corresponding to high level constructs) results in an approximation of the time required to execute the program given adequate resources. By relating the structure of a program to the degree of exhibited parallelism, this method provides a useful tool for studying parallelism and evaluating certain problem classes to be run on similar architecutures.     

Availability analysis for the design of distributed processing networks

This paper presents an analytical model for evaluating the availability of distributed processing systems. The model, which is based on a well-known probability formula, has been implemented in FORTRAN and used for the design of a real-time distributed processing system that requires high availability. It is applied to a sample distributed processing system to illustrate its usefulness and to provide good insight into the design of highly available distributed processing systems. Effects of homogeneous/heterogeneous clustering and standby spare are illustrated. The concept of availability threshold where the distributed system may gain or lose availability over the individual processor availability is introduced. It has proven to be a valuable tool for the tradeoffs in the allocation of system requirements. The concluding remarks summarize the lessons learned and suggest cost-effective ways to achieve higher availability for the design of distributed processing systems.     

Recent advances in the application of thermal infrared scanning to geological and hydrological studies

This paper describes recent advances in the development of thermal scanner technology, data processing techniques and theoretical simulation of field applications at the University of Newcastle. These developments have improved the potential of this method for practical field studies in geology and hydrology in the Australian environment. Improvements in technology have enabled the signal output of the scanner to be stabilized and calibrated by the use of internal, black-body temperature reference sources, prior to recording on magnetic tape. These improvements have opened a new dimension for the analysis and processing of thermal scanner data. Both analog and digital processing methods are used for analysis and presentation. Special presentation methods such as density slicing, contrast stretching, boundary enhancement and contouring are all used to enhance specific aspects of the data, which then assist the interpreter in gleaning additional information about his field problem. Advances have been made by the present group in theoretical studies of soil and rock temperature changes in an active thermal environment. Variations in the ground surface temperature during the diurnal cycle provide information relating to the ground thermal properties. Thus the thermal scanner can be used to study variations in the thermal properties of the ground surface over large areas. The application of thermal scanning to Australian Geological, Hydrogeological and Hydrological problems is discussed.     

Evaluating a data abstraction testing system based on formal specifications

A compiler-based specification and testing system for defining data types has been developed. The system, DAISTS (data abstraction implementation, specification, and testing system) includes formal algebraic specifications and statement and expression test coverage monitors. This paper describes our initial attempt to evaluate the effectiveness of the system in helping users produce software. In an exploratory study, subjects without prior experience with DAISTS were encouraged by the system to develop effective sets of test cases for their implementations. Furthermore, an analysis of the errors remaining in the implementations provided valuable hints about additional useful testing metrics.     

The elastic stability of square perforated plates

A direct matrix method of analysis for the buckling loads on structures, which had already been proven on various structural forms, is applied to the examination of the stability of flat square plates with central square perforations. The results for a variety of boundary conditions are presented for a range of hole to plate size from 0 to 0.8. The method generally shows trends which are different to those predicted by other numerical methods, particularly over the range of the larger hole sizes. Possible reasons for these differences are suggested, but further work to obtain definitive results is clearly needed by all investigators.     

Data and reports: Contents design and users allocation

When a common information system should supply data in a batch processing mode to many various users, the systems analyst is faced with the problem of allocating data among various reports and reports among different users. The traditional approach to that problem is very unstructured. Such a problem is formulated here in a nonlinear binary programming model. Four alternative techniques of solving the model are presented, followed by an example. The main contribution is a systematic and analytic approach toward a major problem in information systems design.     

High-level debugging of distributed systems: The behavioral abstraction approach

Most extant debugging aids force their users to think about errors in programs from a low-level, unit-at-a-time perspective. Such a perspective is inadequate for debugging large complex systems, particularly distributed systems. In this paper, we present a high-level approach to debugging that offers an alternative to the traditional techniques. We describe a language, edl, developed to support this high-level approach to debugging and outline a set of tools that has been constructed to effect this approach. The paper includes an example illustrating the approach and discusses a number of problems encountered while developing these debugging tools.     

层次结构数据在组合框中树形效果的动态实现

为了能使数据库中的层次结构数据在组合框中呈树形结构显示,通过实例分析了如何利用ADO.NET技术实现层次结构数据在TreeView上的动态加载技术,讨论了两种数据在组合框中以树形结构呈现的方法,特别是利用自定义用户控件实现在组合框中加载TreeView控件的方法.     

Guest editor's introduction: Tool and methodology evaluation

The first ACM Sigsoft-sponsored Software Engineering Symposium focused on the issue of evaluating the effectiveness of software engineering tools, techniques, methods, and environments. In this paper we overview and summarize a collection of symposium papers that collectively indicate the state of development in the area of tool and methodology evaluation.     

An analysis of static metrics and faults in C software

In this empirical study, we evaluate the extent to which a set of software measures are correlated with the number of faults and the total estimated repair effort for a large software system. The measures we use are basic counts reflecting program size and structure and metrics proposed by McCabe and Halstead. The effect of program size has a major influence on these metrics, and we present a suitable method of adjusting the metrics for size. In modeling faults or repair effort as a function of one variable, a number of measures individually explain approximately one-quarter of the variation observed in the fault data. No one measure does significantly better than size in explaining the variation in faults found across software units, and thus multiple variable models are necessary to find metrics of importance in addition to program size. The “best” multivariate model explains approximately one-half the variation in the fault data. The metrics included in this model (in addition to size) are: the ratio of block comments to total lines of code, the number of decisions per function, and the relative vocabulary of program variables and operators. These metrics have potential for future use in the quality control of software.     

A software metric for cost estimation and efficiency measurement in data processing system development

The three basic structural elements of a data processing system are shown to be files, flows, and processes. A metric for the size of a data processing system is introduced which is a function of the number of files, flows, and processes of the system. The validity and reliability of this metric are demonstrated. It is shown how the metric may be used to estimate the cost of developing a data processing system at an early stage in the development process. Furthermore, it is demonstrated how the metric may be used to determine the efficiency of data processing system development.     

Generalized path expressions: A high-level debugging mechanism

This paper introduces a modified version of path expressions called Path Rules which can be used as a debugging mechanism to monitor the dynamic behavior of a computation. Path rules have been implemented in a remote symbolic debugger running on the Three Rivers Computer Corporation PERQ computer under the Accent operating system.