Dependability ITV Model-based Analysis and Design of Embedded Software Techniques and methods for Critical Software Anders P. Ravn Aalborg University August.
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Dependability
ITV Model-based Analysis and Design of Embedded SoftwareTechniques and methods for Critical Software
Anders P. RavnAalborg University
August 2011
Basic Concepts
• Availability: readiness for correct service.• Reliability: continuity of correct service.• Safety: absence of catastrophic consequences.• Confidentiality: absence of unauthorized disclosure
of information• Integrity: absence of improper system alterations.• Maintainability: ability to undergo modifications.
Other terms
Threats and Means
Development Phase and Faults
1. the physical world with its natural phenomena,
2. human developers, some possibly lacking competence or having malicious objectives,
3. development tools: software and hardware used by the developers to assist them in the development process.
4. production and test facilities.
Fault * prevention ? * tolerance ? * removal ? * prediction ?
Use Phase and Faults1. the physical world with its natural phenomena,
2. administrators (including maintainers): entities (humans or other systems) that have the authority to manage, modify, repair and use the system; some authorized humans may lack competence or have malicious objectives;
3. users: entities that receive service from the system at their use interfaces;
4. providers: entities that deliver services to the system at its use interfaces;
5. infrastructure: entities that provide specialized services to the system, such as information sources (e.g., time, GPS, etc.), communication links, power sources, cooling airflow, etc.
6. intruders: malicious entities that attempt to exceed any authority they might have and alter service or halt it, alter the system’s functionality or performance, or to access confidential information. Examples include hackers, vandals, corrupt insiders, agents of hostile governments or organizations, and malicious software.
Fault * prevention ? * tolerance ? * removal ? * prediction ?
Elem
entary
Fau
lt
Classes
Combined classification
Failure Modes
Means
Fault
prevention
removal
prediction or forecasting
tolerance
Fault prevention
• Systematic procedures• Clean room (Harlan Mills)• Inspection• Reviews
Fault prevention
• Careful Design
• Conservative Design
• process (activities)
• notations
• tools
• robust functionality
• testability
• tracability
Fault Removal
In Development
1. Verification and validation
2. Diagnosis
3. Correction
In Use• Preventive maintenance• Corrective maintenance• Fault isolation
Verification Techniques
Test approaches
Fault forecasting
• Qualitative evaluation• Quantitative evaluation
Models: Markov-processes, Fault-trees, ...
Fault Forecasting
• Calculation – analysis of design
• Simulation – measurement on design
• Test -- measurement on implementation
Means
Exercise• Where would you add prevention, removal and forecasting
in a V-model process?• What would you add?
Requirements Spec --------------------------- Accpt. Test Report Acceptance Test Spec
Architectural Spec ------------------------ Integr. Test Report Integration Test Spec
Module Interface Spec Module Spec ------------------- Module Test Report
Module Test Spec
Program Source text
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