1 Introduction -- 2 Overview -- 2.1 The Concept of Software Fault-tolerance -- 2.2 Failure Dependence -- 2.3 Evaluation of Reliability of Fault Tolerant Software -- 2.4 Adjudication Mechanisms -- 2.5 Conclusion -- References -- 3 Considerations on Software Diversity on the Basis of Experimental and Theoretical Work -- 3.1 The Different Failure Sets of a Two-fold Diverse System -- 3.2 Experimental Approach -- 3.3 Theoretical Approach -- 3.4 Additional Requirements -- 3.5 Comparison Between Single and Diverse Use of Programs -- 3.6 Conclusion -- References -- 4 The Impact of Forced Diversity on the Failure Behaviour of Multiversion Software -- 4.1 Introduction -- 4.2 Common Failure Behaviour of Forced and Unforced Diverse Systems w. r. t. the Voter Majority -- 4.3 Common Failure Behaviour of Forced and Unforced Diverse Systems w. r. t. the Voter Granularity -- 4.4 Conclusion -- References -- 5 Functional Diversity -- 5.1 Introduction -- 5.2 Limitations of Normal Diversity -- 5.3 Description of Functional Diversity Methodology -- 5.4 Advantages of Functional with respect to Normal Diversity -- 5.5 Disadvantages of Functional Diversity -- 5.6 Application Fields -- 5.7 Choice of the Modelling Approach for Functional Diversity -- 5.8 Classical Semantic Approach -- 5.9 Functional Semantics -- 5.10 Semantic Modelling of Functional Diversity -- 5.11 Functional Diversity Metrication -- 5.12 Definition of Functional Diversity Metrics -- 5.13 Classification of the Metrics -- 5.14 Reliability Analysis for Functionally Diverse Systems -- 5.15 Static Specification Analysis -- 5.16 Reliability Evaluation -- 5.17 Semantic Specification Language -- 5.18 Semantic Specification Analysis Methodology -- References -- 6 Estimation of Failure Correlation in Diverse Software Systems with Dependent Components -- 6.1 Introduction -- 6.2 Evaluation of the Inaccuracy Resulting from the Independence Assumption -- 6.3 The Case of Available Failure Observations -- 6.4 The Case of No Available Failure Observations -- 6.5 Conclusion -- References -- 7 Measurement of Diversity Degree by Quantification of Dissimilarity in the Input Partition -- 7.1 Input Partition and Coverage Diversity -- 7.2 Partition Diversity during the Testing Phase -- 7.3 Conclusion -- References -- 8 Comparison of Mnemonics for Software Diversity Assessment -- 8.1 The Initial Prototype Investigation -- 8.2 Enhancement of the Prototype -- 8.3 Further Improvements to Technique -- 8.4 Conclusions -- References -- 9 The FRIL Model Approach for Software Diversity Assessment -- 9.1 Software Attributes Affecting Diversity -- 9.2 Measuring Diversity -- 9.3 The FRIL Model for Software Diversity Assessment -- 9.4 Extension of the Work -- References -- 10 Reliability Evaluation -- 10.1 Introduction -- 10.2 State of The Art of Reliability Models for Fault Tolerant Software -- 10.3 System States of Fault Tolerant Architectures -- 10.4 Analysis of System Sub-states -- 10.5 Modelling Approach -- 10.6 Modelling Methods -- 10.7 Evaluation of the Equations -- References -- 11 The Impact of Voter Granularity in Fault-Tolerant Software on System Reliability and Availability -- 11.1 Definition of System States -- 11.2 Effect of Voter Granularity on System States -- 11.3 Examples -- 11.4 Strategic Choice of Optimal Granularity -- 11.5 Mixed Solutions -- 11.6 Conclusion -- References -- 12 A Theoretical Evaluation of the Acceptance Test in Recovery Block Programming -- 12.1 Introduction -- 12.2 General Features and Examples of Acceptance Tests -- 12.3 Formal Definition of Acceptance Test Characteristics -- 12.4 An Error Model for the Acceptance Test Behaviour -- 12.5 Conclusion -- References -- 13 Location of Checkpoints by Considering Information Reduction -- 13.1 Introduction -- 13.2 Failure Masking -- 13.3 Function Classes Reducing Information -- 13.4 Impact of Information Reduction on Failure Dependence -- 13.5 Information Reduction for Binary Values -- 13.6 Location of Checkpoints -- 13.7 Example -- 13.8 Conclusion -- References -- 14 Conclusions -- 14.1 Hardware Failure vs. Software Failure -- 14.2 Diversity and the Design of Fault-tolerant Software Systems -- 14.3 Assessment of Software Fault-tolerance -- 14.4 Prospect.