Software reliability through fault-avoidance and fault-tolerance

The use of back-to-back, or comparison, testing for regression test or porting is examined. The efficiency and the cost of the strategy is compared with manual and table-driven single version testing. Some of the key parameters that influence the efficiency and the cost of the approach are the failure identification effort during single version program testing, the extent of implemented changes, the nature of the regression test data (e.g., random), and the nature of the inter-version failure correlation and fault-masking. The advantages and disadvantages of the technique are discussed, together with some suggestions concerning its practical use

Experiments in fault tolerant software reliability

Twenty functionally equivalent programs were built and tested in a multiversion software experiment. Following unit testing, all programs were subjected to an extensive system test. In the process sixty-one distinct faults were identified among the versions. Less than 12 percent of the faults exhibited varying degrees of positive correlation. The common-cause (or similar) faults spanned as many as 14 components. However, a majority of these faults were trivial, and easily detected by proper unit and/or system testing. Only two of the seven similar faults were difficult faults, and both were caused by specification ambiguities. One of these faults exhibited variable identical-and-wrong response span, i.e. response span which varied with the testing conditions and input data. Techniques that could have been used to avoid the faults are discussed. For example, it was determined that back-to-back testing of 2-tuples could have been used to eliminate about 90 percent of the faults. In addition, four of the seven similar faults could have been detected by using back-to-back testing of 5-tuples. It is believed that most, if not all, similar faults could have been avoided had the specifications been written using more formal notation, the unit testing phase was subject to more stringent standards and controls, and better tools for measuring the quality and adequacy of the test data (e.g. coverage) were used

Multiversion software reliability through fault-avoidance and fault-tolerance

In this project we have proposed to investigate a number of experimental and theoretical issues associated with the practical use of multi-version software in providing dependable software through fault-avoidance and fault-elimination, as well as run-time tolerance of software faults. In the period reported here we have working on the following: We have continued collection of data on the relationships between software faults and reliability, and the coverage provided by the testing process as measured by different metrics (including data flow metrics). We continued work on software reliability estimation methods based on non-random sampling, and the relationship between software reliability and code coverage provided through testing. We have continued studying back-to-back testing as an efficient mechanism for removal of uncorrelated faults, and common-cause faults of variable span. We have also been studying back-to-back testing as a tool for improvement of the software change process, including regression testing. We continued investigating existing, and worked on formulation of new fault-tolerance models. In particular, we have partly finished evaluation of Consensus Voting in the presence of correlated failures, and are in the process of finishing evaluation of Consensus Recovery Block (CRB) under failure correlation. We find both approaches far superior to commonly employed fixed agreement number voting (usually majority voting). We have also finished a cost analysis of the CRB approach

Software reliability through fault-avoidance and fault-tolerance

Twenty independently developed but functionally equivalent software versions were used to investigate and compare empirically some properties of N-version programming, Recovery Block, and Consensus Recovery Block, using the majority and consensus voting algorithms. This was also compared with another hybrid fault-tolerant scheme called Acceptance Voting, using dynamic versions of consensus and majority voting. Consensus voting provides adaptation of the voting strategy to varying component reliability, failure correlation, and output space characteristics. Since failure correlation among versions effectively reduces the cardinality of the space in which the voter make decisions, consensus voting is usually preferable to simple majority voting in any fault-tolerant system. When versions have considerably different reliabilities, the version with the best reliability will perform better than any of the fault-tolerant techniques

Experiments in fault tolerant software reliability

The reliability of voting was evaluated in a fault-tolerant software system for small output spaces. The effectiveness of the back-to-back testing process was investigated. Version 3.0 of the RSDIMU-ATS, a semi-automated test bed for certification testing of RSDIMU software, was prepared and distributed. Software reliability estimation methods based on non-random sampling are being studied. The investigation of existing fault-tolerance models was continued and formulation of new models was initiated

Reliability of voting in fault-tolerant software systems for small output spaces

Under a voting strategy in a fault-tolerant software system there is a difference between correctness and agreement. An independent N-version programming reliability model is proposed for treating small output spaces which distinguishes between correctness and agreement. System reliability is investigated using analytical relationships and simulation. A consensus majority voting strategy is proposed and its performance is analyzed and compared with other voting strategies. Consensus majority strategy automatically adapts the voting to different component reliability and output space cardinality characteristics. It is shown that absolute majority voting strategy provides a lower bound on the reliability provided by the consensus majority, and 2-of-n voting strategy an upper bound. If r is the cardinality of the output space it is proved the 1/r is a lower bound on the average reliability of fault-tolerant system components below which the system reliability begins to deteriorate as more versions are added

The pedogenesis of tin- and sulfide-lode mineralization at True Hill, southwestern New Brunswick

The subvolcanic True Hill granite porphyry in southwestern New Brunswick is genetically related to the Beech Hill series of granites of Devono-Carboniferous age. Three True Hill (TH) greisenised granite porphyry cupolas host Bi-Sn-Mo-W mineralized zones that have similarities to the nearby W-Mo-Bi orebodies at Mount Pleasant (MP). Tin-bearing lodes (0.03 to 0.66 wt, % Sn) are developed along faults and fractures that cut both mineralized (Bi-Sn-Mo-W) and unmineralized True Hill granite porphyry and enclosing metasedimentary rocks of the Waweig Formation. Within these lodes, particularly the central Main lode, two types of mineralization are present, an early chlorite-sulfide assemblage (Stage 1) and a later hematite-phengite-cassiterite assemblage (Stage 2) that replaces, in part, the earlier Stage 1 assemblage. The Stage 1 assemblage consists of Fe-rich septechlorite, pyrite, low-Fe sphalerite, magnetite, chalcopyrite, galena, Pb-Bi sulfides, tennantite, arsenopyrite and native Ag. Fe-Mg-Mn metasomatism responsible for chloritization was coincident with leaching of alkali and alkali-earth elements during feldspar hydrolysis. The Stage 1 assemblage (chl-sulfide) was formed at low temperature (<200°C) and low oxygen fugacity. The Stage 2 assemblage includes hematite, phengite, cassiterite and monazite with minor late quartz and fluorite. This assemblage was deposited at slightly higher temperatures (200"-300°CX higher oxygen fugacity (above hematite magnetite buffer) and at moderate pH 's (<musc-Kfs buffer). The overprinting of Stage 2 assemblages on portions of Stage 1 locally produces complex textures within the lodes at True Hill. The composition of both Stage 1 and 2 assemblages in the lodes is controlled by the (i) host rock composition and (ii) the mineralizing hydrothermal fluids. The deposition of Sn and LREE from Stage 2 fluids formed cassiterite and monazite along the reaction front between Stage 2 assemblages and chlorite-sulfide (Stage 1) and granite. Deposition of cassiterite probably occurred in response to (i) an increase in the Fe-Cl complexing at the expense of Sn- and LREE-C1 complexes during interation with Stage 1 assemblages, (ii) an increase in pH due to the feldspar hydrolysis in the granite and (iii) cooling of the fluid by the host rock. Although uneconomic, tin-sulfide lodes at True Hill have similarities with lodes developed within the North Zone of Mount Pleasant (New Brunswick) and Cornwall (England). However, the association of hematite and phengite with cassiterite mineralization is unique to this deposit RÉSUMÉ Le porphyre granitique subvolcanique de True Hill (Nouveau-Brunswick méridional) est lié par sa genèse au cortege granitique dévono-carbonifère de Beech Hill. Trois coupoles de porphyre granitique de True Hill (TH) altéré en greisen renferment des zones minéralisées en Bi-Sn-Mo-W et qui montrent des similitudes avec les gisements voisins de W-Mo-Bi présents a Mount Pleasant (MP). Des faisceaux filoniens porteurs d'étain (0,03 à 0,66% pds. Sn) s'installent le long de failles et de cassures recoupant les porphyres granitiques de True Hill, tant minéralises que stériles, ainsi que leur encaissant métasédimentaire (Formation de Waweig). Au sein de ces faisceaux, et surtout du faisceau central principal, on note deux types de minéralisation: un assemblage précoce à chlorite-sulfure (stage 1) et un assemblage tardif à hématite-phengite-cassitérite (stage 2) qui remplace en partie le premier. L'assemblage représentant le stage 1 consiste en de la septechlorite riche en Fe, de la pyrite, de la blende pauvre en Fe, de la magnétite, de la chalcopyrite, de la galène, des sulfures à Pb-Bi, de la tennantite, du mispickel et de l'argent natif. La métasomatose des Fe-Mg-Mn, dont provient la chloritisation, s'accompagne d'un lessivage des éléments alcalins et alcalino-terreux durant l’hydrolyse des feldspaths. L'assemblage denotant le stage 1 (chlorite-sulfures) se forma à basse température (<200°C) et faible fugacite d'oxygene. L'assemblage traduisant le stage 2 comporte de l'hématite, de la phengite, de la cassitérite, ainsi que de la monazite avec de faibles quantités de quartz et de fluorine tardifs. Cet assemblage fait inlervenir des températures un peu plus élevées (200°C a 300°C), une fugacité d'oxygène plus élevée (au-dessus du tampon hématite-magnétite) et des pH modérés (en-dessous du tampon des feldspaths potassiques de la muscovite). La surimpression des assemblages représentant le stage 2 sur des portions du stage 1 produit localement des textures complexes au sein des faisceaux filoniens de True Hill. La composition des assemblages dénotant tant le stage 1 que le stage 2 au sein de ces faisceaux est régie par: (i) la composition de l'encaissant et (ii) les étutdes minéralisateurs hydrothermaux. Le dépôt d'euin et de T.R. légères à paitir des fluides du stage 2 engendra de la cassitérite et de la monazite le long du front réactionnel, entre les assemblages témoins du stage 2, les chlorite-sulfures et le granite. Le dépôt de la cassitérite est probablement le fruit de: (i) une augmentation de la formation de complexes à Fe-Cl aux depens des complexes à Snet à Cl-T.R. légères durant l’interaction avec des assemblages du stage l,(ii)une élévation du pH par suite de 1 l’hydrolyse des feldspaths du granite, et (iii) le refroidissement du fluide par rencaissant Bien que de nature non économique, les faisceaux filoniens à étain et à sulfures présents à True Hill ne sont pas sans rappeler les faisceaux développés dans la Zone Nord de Mount Pleasant (Nouveau-Bnmswick) et à Cornwall (Angleterre). Cependant, ce gisement se singularise par l’association d'hématite et de phengite avec la minéralisation en cassitérite. [Traduit par le journal

Software reliability through fault-avoidance and fault-tolerance

Strategies and tools for the testing, risk assessment and risk control of dependable software-based systems were developed. Part of this project consists of studies to enable the transfer of technology to industry, for example the risk management techniques for safety-concious systems. Theoretical investigations of Boolean and Relational Operator (BRO) testing strategy were conducted for condition-based testing. The Basic Graph Generation and Analysis tool (BGG) was extended to fully incorporate several variants of the BRO metric. Single- and multi-phase risk, coverage and time-based models are being developed to provide additional theoretical and empirical basis for estimation of the reliability and availability of large, highly dependable software. A model for software process and risk management was developed. The use of cause-effect graphing for software specification and validation was investigated. Lastly, advanced software fault-tolerance models were studied to provide alternatives and improvements in situations where simple software fault-tolerance strategies break down

Association between Impaired Lung Function and Cardiovascular Disease. Cause, Effect, or Force of Circumstance?

No abstract available

Pulmonary artery stiffness in chronic obstructive pulmonary disease (copd) and emphysema: The Multi-Ethnic Study of Atherosclerosis (MESA) COPD Study

Purpose: Chronic obstructive pulmonary disease (COPD) and particularly emphysema are characterized by stiffness of the aorta, due in part to accelerated elastin degradation in the lungs and aorta. Stiffness of the pulmonary arteries (PAs) may also be increased in COPD and emphysema, but data are lacking. We assessed PA stiffness using MRI in patients with COPD and related these measurements to COPD severity and percent emphysema. Materials and Methods: The Multi-Ethnic Study of Atherosclerosis (MESA) COPD Study recruited 290 participants, age 50–79 years with 10 or more packyears and free of clinical cardiovascular disease. COPD severity were defined on postbronchodilator spirometry by ATS/ERS criteria. Percent emphysema was defined as the percentage of regions of the lung < -950 Hounsfield units on full-lung computed tomography (CT). PA stain was defined by the percent change in cross-sectional PA area between systole and diastole on MRI. Blood flow across the tricuspid and mitral valves was assessed by phase-contrast MRI for determination of the ventricular diastolic dysfunction (E/A ratio). Results: PA strain was reduced in COPD compared with controls (P = 0.002) and was inversely correlated with COPD severity (P = 0.004). PA strain was inversely associated to percent emphysema (P = 0.01). PA strain was also markedly correlated with right ventricular diastolic dysfunction measured by E/A ratios in the fully adjusted mix models (P = 0.02). Conclusion: PA strain is reduced in COPD, related in part to percent emphysema on CT scan, which may have implications for pulmonary small vessel flow and right ventricular function. Level of Evidence: 2 Technical Efficacy: Stage