Libyan International University Lecture 2 On Formal Models and Methods PDF

Libyan International University Formal Models and Methods Lecture 2 Dr. Salwa Elakeili Faculty of Information Technology  Outline Importance of proof (Cont) Overview of Formal Methods for Software Specification and Analysis Testing: Sta...

Libyan International University Formal Models and Methods Lecture 2 Dr. Salwa Elakeili Faculty of Information Technology  Outline Importance of proof (Cont) Overview of Formal Methods for Software Specification and Analysis Testing: Static vs Dynamic Analysis Failing Software Costs Money Failing Software Costs lives Concepts What are Formal Methods? Importance of proof (Cont) The construction of proofs is an essential part of writing a specification. A specification without proofs is untested: it may be inconsistent; ; it may defines unexpected properties; or omit those that were; it may make inappropriate assumptions. The practice of proof makes for better specifications why proof is crucial in formal methods: Ensuring Correctness: Formal proofs verify that a system behaves exactly as specified. This eliminates ambiguities that may arise from informal design methods. Error Detection: Proof-based methods detect errors early in the development process, reducing the cost of fixing bugs later on. Security Assurance: In safety-critical systems (medical devices), proof ensures that the system meets stringent security and performance standards. Unambiguous Communication: Formal proofs provide a clear and unambiguous way of communicating system behaviors between developers and stakeholders. Automation: With the use of theorem provers and model checkers, parts of the proof process can be automated, making formal verification more scalable.  Formal Methods for Software Specification and Analysis: An Overview ❑ Every Software engineering methodology is based on a recommended development process proceeding through several phases: ▪ Analysis, ▪ Specification, ▪ Design, ▪ Coding, ▪ Unit Testing, ▪ Integration and System testing, ▪ Maintenance ❑Formal Methods can: Be a foundation for describing complex systems Be a foundation for reasoning about systems Provide support for program development  Testing: Static vs Dynamic Analysis ❑ Static analysis of code does not require execution of code ❑Static analysis of the code can assist testing in deriving adequacy criteria ❑ It is used to find errors, security vulnerabilities, code inefficiencies, and deviations from coding standards early in the development process. By performing a detailed examination of the code’s structure, syntax, and logical flow, static analysis helps improve software quality and reduce the cost of fixing bugs later on.  Key Characteristics of Static Analysis: Non-execution-based: static analysis checks the code's structure, potential paths, and logic at compile-time or even earlier. Tool-driven: Automated tools are used to scan and analyze the code. These tools can detect patterns, vulnerabilities, and issues based on predefined rules and algorithms. Early Bug Detection: Since static analysis occurs early in the software development lifecycle, it helps identify potential problems before the software is even run, preventing defects from being introduced into later stages. ❑Dynamic Analysis of code involves running the system (testing) Program run formally under controlled conditions with specific results expected Dynamic analysis is crucial for understanding how software performs under different conditions and for identifying issues that may only arise during runtime, such as performance bottlenecks, and security vulnerabilities. dynamic analysis of the code can be used to assess whether the criteria have been met Path and Branch testing Types of Dynamic Analysis Unit testing Integration testing System testing Performance testing Security testing  Facts ❑ Software has become critical to modern life. ❑ Process Control (Oil, gas, water,…) ❑Transportation (air traffic control,….) ❑ Health Care (patient monitoring, device control,..) ❑ Finance (automatic trading, bank security,..) Failing Software costs Money and Life  Failing Software Costs Money ❑ Thousands of dollars for each minute of factory down- time ❑ Business failures associated with buggy software ❑Example ❑Knight Capital, a major player in the stock market, suffered a catastrophic software failure in August 2012. A bug in their trading algorithm caused the firm to make erroneous trades, resulting in a loss of $440 million in just 45 minutes. The faulty deployment of new software that interacted with an old system caused a cascade of trades that the company was unable to control. The financial hit was so severe that Knight Capital had to seek emergency funding and eventually merged with another company to survive.  Failing Software Costs lives Potential problems are obvious: Software used to control nuclear power plants (‫)محطات الطاقة النووية‬ Air-traffic control systems (‫) نظم مراقبة الحركة الجوية‬ Embedded software in cars Spacecraft launch vehicle control (‫)مركبة فضائية إطالق السيطرة على المركبة‬  Therac-25 Case: The Therac-25 was a radiation therapy machine used to treat cancer patients. It had software that controlled its functions, including delivering high doses of radiation to specific areas of the body. However, due to software bugs in its control system, the machine malfunctioned and administered massive overdoses of radiation to patients. Between 1985 and 1987, six patients were severely injured, and three of them died as a direct result of radiation overdoses caused by the software errors. The issue stemmed from inadequate safety checks and poor handling of errors in the software code.  Concepts ❑ Current methods of SW development involves only combination of diagrams, text, tables etc. ❑No methods are used to test the correctness of the end result in each of stages of SW development for e.g. requirement specification, design etc.. ❑This may lead to ambiguities, incompleteness.. ❑ This may not be a good option for safety critical systems (SCSs) where failure may have high price.  Formal methods Formal methods are intended to systematize and introduce rigor into all the phases of software development. It helps us avoid ignoring critical issues, provides a standard means to record various assumptions and decisions, and forms a basis for consistency among many related activities. In use since late 1970s more popular in Europe than US still only a niche market  Formal Methods ❑ Past years of the formal methods Unclear notation ‫تدوين غامض‬ Non-scalable techniques ‫تقنيات غير قابلة للتطوير‬ Inadequate tool support ‫دعم أداة غير كافية‬ Hard to use tools ‫من الصعب استخدام األدوات‬ Very few case studies ‫عدد قليل جدا من دراسات الحالة‬ ❑ Nowadays Trying to find more rigorous notation ‫تحاول أن تجد تدوين‬ ‫أكثر صرامة‬ More industries case studies Researchers try to gain benefits of using formal methods ‫يحاول الباحثون الحصول على فوائد استخدام األساليب الرسمية‬  What are Formal Methods ❑ Formal methods and testing are two important approaches that assist in development of high quality software ❑ By using formal methods and testing together, we can reduce the cost of development by applying testing techniques much earlier in the lifecycle while defects are relatively inexpensive to correct. ‫ يمكننا تقليل تكلفة التطوير من خالل‬، ‫باستخدام األساليب الرسمية واالختبار معًا‬ ‫تطبيق تقنيات االختبار في وقت مبكر جدًا من دورة الحياة بينما العيوب غير مكلفة‬ ‫نسبيًا لتصحيح‬ ❑ Techniques and tools based on mathematics and formal logic What are Formal Methods (Cont) ❑ Formal methods are applied to Safety Critical Systems (SCS) or security-critical software and systems ❑ Safety-critical systems are those systems whose failure could result in loss of life, significant property damage, or damage to the environment. ❑ Formal methods aim to increase our understanding of a system by revealing errors ❑ Can assume various forms and levels of rigor  In systems where the failure must be avoided, the use of formal method can be justified and is likely to be cost effective The use of formal methods is increasing in specialized in critical system development where emergent system properties such as ( safety, reliability and security) are very important. These critical systems have very high validation costs and the costs of system failure are large and are increasing. Formal methods are being used because they can reduce these costs Summary Formal methods and evaluation are two critical techniques to help develop high-quality software. Safety-critical systems are those systems whose failure could result in loss of life, significant property damage, or damage to the environment.