A study of systems implementation languages for the POCCNET system

The results are presented of a study of systems implementation languages for the Payload Operations Control Center Network (POCCNET). Criteria are developed for evaluating the languages, and fifteen existing languages are evaluated on the basis of these criteria

Supervising Offline Partial Evaluation of Logic Programs using Online Techniques

A major impediment for more widespread use of offline partial evaluation is the difficulty of obtaining and maintaining annotations for larger, realistic programs. Existing automatic binding-time analyses still only have limited applicability and annotations often have to be created or improved and maintained by hand, leading to errors. We present a technique to help overcome this problem by using online control techniques which supervise the specialisation process in order to help the development and maintenance of correct annotations by identifying errors. We discuss an implementation in the Logen system and show on a series of examples that this approach is effective: very few false alarms were raised while infinite loops were detected quickly. We also present the integration of this technique into a web interface, which highlights problematic annotations directly in the source code. A method to automatically fix incorrect annotations is presented, allowing the approach to be also used as a pragmatic binding time analysis. Finally we show how our method can be used for efficiently locating built-in errors in Prolog source code

Development and analysis of the Software Implemented Fault-Tolerance (SIFT) computer

SIFT (Software Implemented Fault Tolerance) is an experimental, fault-tolerant computer system designed to meet the extreme reliability requirements for safety-critical functions in advanced aircraft. Errors are masked by performing a majority voting operation over the results of identical computations, and faulty processors are removed from service by reassigning computations to the nonfaulty processors. This scheme has been implemented in a special architecture using a set of standard Bendix BDX930 processors, augmented by a special asynchronous-broadcast communication interface that provides direct, processor to processor communication among all processors. Fault isolation is accomplished in hardware; all other fault-tolerance functions, together with scheduling and synchronization are implemented exclusively by executive system software. The system reliability is predicted by a Markov model. Mathematical consistency of the system software with respect to the reliability model has been partially verified, using recently developed tools for machine-aided proof of program correctness

Preliminary design of the redundant software experiment

The goal of the present experiment is to characterize the fault distributions of highly reliable software replicates, constructed using techniques and environments which are similar to those used in comtemporary industrial software facilities. The fault distributions and their effect on the reliability of fault tolerant configurations of the software will be determined through extensive life testing of the replicates against carefully constructed randomly generated test data. Each detected error will be carefully analyzed to provide insight in to their nature and cause. A direct objective is to develop techniques for reducing the intensity of coincident errors, thus increasing the reliability gain which can be achieved with fault tolerance. Data on the reliability gains realized, and the cost of the fault tolerant configurations can be used to design a companion experiment to determine the cost effectiveness of the fault tolerant strategy. Finally, the data and analysis produced by this experiment will be valuable to the software engineering community as a whole because it will provide a useful insight into the nature and cause of hard to find, subtle faults which escape standard software engineering validation techniques and thus persist far into the software life cycle

Investigation, Development, and Evaluation of Performance Proving for Fault-tolerant Computers

A number of methodologies for verifying systems and computer based tools that assist users in verifying their systems were developed. These tools were applied to verify in part the SIFT ultrareliable aircraft computer. Topics covered included: STP theorem prover; design verification of SIFT; high level language code verification; assembly language level verification; numerical algorithm verification; verification of flight control programs; and verification of hardware logic

A project to investigate mechanisms and methodologies for the design and construction of communicating concurrent processes in real-time environments

Research undertaken in 1979 into effective and appropriate mechanisms to aid in the design and construction of software for use in the flight research programs undertaken by NASA is presented

Musical Program Auralisation: Empirical Studies

Program auralisation aims to communicate information about program state, data, and behaviour using audio. We have argued that music offers many advantages as a communication medium [1]. The CAITLIN system [4, 16, 17, 18] was constructed to provide auralisations within a formal structured musical framework. Pilot studies [4, 16] showed that programmers could infer program structure from auralisations alone. A study was conducted using twenty-two novice programmers to assess a) whether novices could understand the musical auralisations and b) whether the musical experience and knowledge of subjects affected their performance. The results show that novices could interpret the auralisations (with accuracy varying across different levels of abstraction) and that musical knowledge had no significant effect on performance. A second experiment was conducted with another twenty-two novice programmers to study the effects of musical program auralisation on debugging tasks. The experiment aimed to determine whether auralisations would lead to higher bug detection rates. The results indicate that, in certain circumstances, musical auralisations can be used to help locate bugs in programs and that musical skill does not affect the ability to make use of the auralisations. In addition, it the experiment showed that subjective workload increased when the musical auralisations were used

DYNAMICS OF FOOD PRICE INFLATION

A supply-shift concept of food price inflation is offered as an explanation of why food prices have increased in recent years. This view is consistent with cost-push theories of inflation. The effects of higher farm product prices on food prices are analyzed using Pascal distributed lag models of the price adjustment process. Estimates are presented for 23 selected food products. The results indicate that higher farm prices are passed through to the retail level most quickly for food products which are not highly processed.Demand and Price Analysis,