Reliable Cycles and Formal Techniques and Constancy

Reliable cycles and Formal techniques and constancy Trustworthy cycles • To ensure a minimal number of software defects, it is important to have a defined, repeatable software process. • A defined repeatable process is one that doesn't rely solely on individual skills; it can be executed by different people. • Controllers use information about the process to verify that good software practices have been used. • For defect detection, the process activities should include significant effort dedicated to verification and validation. Trustworthy interaction attributes • Explicitly defined o • A process that has a defined process model used to drive the software development process. Data should be collected during the process to demonstrate that the development team has followed the process as defined in the model. Repeatable o A process that does not depend on individual interpretation and judgment. The process can be repeated across projects and with different teams, regardless of who is involved in development. Trustworthy cycle activities • Requirements reviews to ensure that the requirements are, as much as possible, complete and consistent. • Requirements management to ensure that changes to the requirements are controlled and that the impact of proposed requirements changes is understood. • Formal specification, where a mathematical model of the software is created and analyzed. • System modeling, where the software design is clearly documented as a set of graphical models, and the relationships between the requirements and these models are documented. 1 • Design and program reviews, where the different descriptions of the system are evaluated and reviewed by different individuals. • Static analysis, where automated checks are carried out on the source code of the program. • Test planning and management, where a comprehensive set of system tests is designed. o The testing strategy must be carefully formulated to ensure that these tests provide coverage of the system requirements and have been correctly applied in the testing strategy. Trustworthy cycles and agility • Reliable software often requires verification, so both process and product documentation must be produced. • Early requirements analysis is also essential to identify requirements and conflicts that might compromise the safety and security of the system. • These conflict with the general approach in agile development of co-evolving requirements and systems and minimizing documentation. • An agile process can be defined that combines methods such as iterative development, test-first development, and customer interaction in the development team. • As long as the team follows that process and documents their activities, agile methods can be used. • However, additional documentation and planning are necessary, so "pure agile" is impractical for reliable systems engineering. Formal specification • Formal methods are approaches to software development that rely on mathematical representation and analysis of software. • Formal methods include: o Formal specification; o Specification analysis and verification; o Transformational development; o Program verification. 2 • Formal methods significantly reduce certain types of software errors and can be cost-effective for reliable systems engineering. Formal methodologies • • Check-based approaches o Different descriptions of a software system, such as a specification and a program implementing that specification, are shown to be the same. o This demonstrates the absence of execution errors. Refinement-based approaches o A description of a system is systematically transformed into another, lower-level representation — for example, a specification is transformed automatically into an implementation. o This ensures that, if the transformation is correct, the descriptions are equivalent. Utilization of formal methods • The primary benefits of formal methods are in reducing the number of defects in systems. • Therefore, their main area of applicability is in reliable systems engineering. There have been several successful projects where formal methods have been used in this context. • In this domain, the use of formal methods is likely to be cost-effective because high system failure costs must be avoided. Categories of error • Specification and design errors and omissions o • Creating and analyzing a formal model of the software may uncover errors and omissions in the software requirements. If the model is produced systematically from source code, analysis using model checking can find undesirable states that might occur, such as deadlock in a concurrent system. Inconsistencies between a specification and a program o If a refinement approach is used, mistakes made by developers that make the software inconsistent with the specification are avoided. 3 Program modeling finds inconsistencies between a program and its specification. Advantages of formal specification • Developing a formal specification requires the system requirements to be thoroughly analyzed. This helps identify problems, inconsistencies, and deficiencies in the requirements. • Since the specification is expressed in a formal language, finding inconsistencies and incompleteness can be analyzed automatically. • If you use a formal method such as the B method, you can transform the formal specification into a "correct" program. • Program testing costs may be reduced if the program is formally checked against its specification. 4