1. Safety-Critical Systems Dependability
Engineering and International Standards
Saleh Al-Da’ajeh
Saleh.aldaajeh@adpoly.ac.ae
http://www.adpoly.ac.ae
December 23, 2012
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2. 1Introduction
Overview
Safety -Critical Systems
Safety -Critical Systems Applications, Characteristics, and
other Terminologies
2Dependability
Taxonomy
Threats on Safety -Critical Systems Dependability
Dependability Attributes
3Means to Achieve Dependability
Achieving Dependability Quality Attributes
4Summary

3. Software Systems Development
Development Phases
Introduction
Overview
Safety -Critical Systems
Safety -Critical Systems
Applications, Characteristics,
and other Terminologies
Dependability
Taxonomy
Threats on Safety -Critical
Systems Dependability
Dependability Attributes
Means to Achieve
Dependability
Achieving Dependability
Quality Attributes
Summary
Figure: Waterfall Model - Typical Software Development Phases
Saleh Al-Da’ajeh Safety-Critical Systems Dependability December 23, 2012 3/16

4. Problems Developing Software Systems
Software Engineers Role in Solving Problems
Introduction
Overview
Safety -Critical Systems
Safety -Critical Systems
Applications, Characteristics,
and other Terminologies
Dependability
Taxonomy
Threats on Safety -Critical
Systems Dependability
Dependability Attributes
Means to Achieve
Dependability
Achieving Dependability
Quality Attributes
Summary
Saleh Al-Da’ajeh Safety-Critical Systems Dependability December 23, 2012 4/16

5. Safety-Critical Systems
Definition and Applications
Introduction
Overview
Safety -Critical Systems According to John C. Knight, Safety Critical Systems are those
Safety -Critical Systems
Applications, Characteristics, systems whose failure could result in a catastrophic consequences
and other Terminologies
such as loss in life.
Dependability
Taxonomy Examples of Safety-Critical Systems Applications and
Threats on Safety -Critical
Systems Dependability
Catastrophic Consequences:
Dependability Attributes
Loss of the Mars Polar Lander 1999, cost 110 million $
Means to Achieve
Dependability
Emergency Shut-down of the Hatch Nuclear Power Plant,
Achieving Dependability March 7th, 2008 - Software Update.
Quality Attributes
Power Outage across Northeastern U.S. and Southeastern
Summary
Canada, August 2003, cost 14 billion $
Airplanes crashes such as the American Airlines -Flight 965,
Korean Air-Flight 801, Air France- Flight 447.
Saleh Al-Da’ajeh Safety-Critical Systems Dependability December 23, 2012 5/16

6. Safety-Critical Systems Applications
Common Characteristics, and Other Terminologies
Introduction
Overview
Safety -Critical Systems
Safety -Critical Systems Safety-critical systems are also known as:
Applications, Characteristics,
and other Terminologies
Real-Time Systems
Dependability
Taxonomy
and some times known as "‘Embedded Systems"’ according to
Threats on Safety -Critical their existing environment.
Systems Dependability
Dependability Attributes
Different type of safety-critical systems shares four common
Means to Achieve
Dependability
requirements:
Achieving Dependability
Quality Attributes Real-time constraints
Summary
Dependability
Resources consumption
and Long-Operating life.
Saleh Al-Da’ajeh Safety-Critical Systems Dependability December 23, 2012 6/16

7. Safety-Critical Systems Dependability
Fundamental Concepts of Dependability
Introduction
Overview
Safety -Critical Systems
Safety -Critical Systems
Applications, Characteristics,
and other Terminologies
Dependability is the property of a system that delivers
Dependability
Taxonomy
justifiably services at a reliance level and the ability of the
Threats on Safety -Critical
Systems Dependability
system to avoid failures that are serious and numerous.
Dependability Attributes
The concept dependability consists of three main parts
Means to Achieve
Dependability Threats
Achieving Dependability
Quality Attributes Attributes
Summary
Means
Saleh Al-Da’ajeh Safety-Critical Systems Dependability December 23, 2012 7/16

8. Dependability Taxonomy
Dependability Exposed
Introduction
Overview
Safety -Critical Systems
Safety -Critical Systems
Applications, Characteristics,
and other Terminologies
Dependability
Taxonomy
Threats on Safety -Critical
Systems Dependability
Dependability Attributes
Means to Achieve
Dependability
Achieving Dependability
Quality Attributes
Summary
Figure: Dependability Taxonomy
Saleh Al-Da’ajeh Safety-Critical Systems Dependability December 23, 2012 8/16

9. The Threats: Faults, Error, Failure
Faults are further investigated enclosing various aspects such as phase of creation
Introduction
Overview
or occurence of faults, system boundaries, domain, phenomenological cause, intent,
Safety -Critical Systems
and presistance of faults.
Safety -Critical Systems Failures are discussed covering different aspects such as the domain of the failures,
Applications, Characteristics,
and other Terminologies controllability of the failures, consistency of the failures, consequences of the
failure.
Dependability
Taxonomy
Threats on Safety -Critical
Systems Dependability
Dependability Attributes
Means to Achieve
Dependability
Achieving Dependability
Quality Attributes
Summary
Figure: Relationship between Error, Faults, and Failures
Saleh Al-Da’ajeh Safety-Critical Systems Dependability December 23, 2012 9/16

10. Faults Analysis
Introduction
Overview
Safety -Critical Systems
Safety -Critical Systems
Applications, Characteristics,
and other Terminologies
Dependability
Taxonomy
Threats on Safety -Critical
Systems Dependability
Dependability Attributes
Means to Achieve
Dependability
Achieving Dependability
Quality Attributes
Summary
Saleh Al-Da’ajeh Safety-Critical Systems Dependability December 23, 2012 10/16

11. Failure Analysis
Introduction
Overview
Safety -Critical Systems
Safety -Critical Systems
Applications, Characteristics,
and other Terminologies
Dependability
Taxonomy
Threats on Safety -Critical
Systems Dependability
Dependability Attributes
Means to Achieve
Dependability
Achieving Dependability
Quality Attributes
Summary
Saleh Al-Da’ajeh Safety-Critical Systems Dependability December 23, 2012 11/16

12. Attributes According to the Larpie and /ISO 9126
Introduction
Overview Dependability consists of a subset of quality attributes that can be classified into
Safety -Critical Systems run-time quality attributes, and non-run time quality attributes:
Safety -Critical Systems
Applications, Characteristics,
and other Terminologies
Run-time Attributes
Dependability Availability: readiness of service for authorized users
Taxonomy Reliability: continuity of service. The system is expected to
Threats on Safety -Critical
Systems Dependability
perform its task in spite of the existence of some faults.
Dependability Attributes Integrity: non-occurrence of improper alternation of
Means to Achieve
information.
Dependability Confidentiality: non-occurrence of unauthorized disclosure of
Achieving Dependability
Quality Attributes information as system data and programs are resistant to
unauthorized modifications.
Summary
Safety: non-occurrence of catastrophic consequences for the
user(s) and in the operation environment.
Non Run-time attributes:
Maintainability: aptitude to undergo repairs and evolution
Saleh Al-Da’ajeh Safety-Critical Systems Dependability December 23, 2012 12/16

13. Achieving Dependability Quality Attributes
Verification, Validation, and Engineering
Introduction
Overview
Safety -Critical Systems
Safety -Critical Systems The oldest methods, approaches, and techniques undertaken
Applications, Characteristics,
and other Terminologies
to achieve dependability quality attributes are nowadays
Dependability depicted as verification and validation activities; falling into
Taxonomy
Threats on Safety -Critical the software testing stage.
Systems Dependability
Dependability Attributes The very recent mechanisms undertaken to achieve the
Means to Achieve various dependability quality attributes are focused on
Dependability
Achieving Dependability engineering quality attributes at the early stages, such as
Quality Attributes
balancing the quality attributes relationships by utilizing the
Summary
most suitable architectural strategies and patterns for the
software systems.
Saleh Al-Da’ajeh Safety-Critical Systems Dependability December 23, 2012 13/16

14. Means to Achieve Dependability to Safety
-Critical Systems
Introduction
Overview
Safety -Critical Systems Although dependability quality attributes achievement is
Safety -Critical Systems
Applications, Characteristics,
strongly related to the software architecture stage, yet
and other Terminologies
almost all the means undertaken to achieve dependability
Dependability
Taxonomy quality attributes are usually left to be used in late stages of
Threats on Safety -Critical
Systems Dependability
the software development life-cycle.
Dependability Attributes
Attaining dependability quality attributes is never isolated
Means to Achieve
Dependability to a distinct stage nor a certain technique/approach.
Achieving Dependability
Quality Attributes Means adopted by dependability engineers are as follow:
Summary Fault Prevention
Fault Tolerance
Fault Removal
Fault Forecasting
Saleh Al-Da’ajeh Safety-Critical Systems Dependability December 23, 2012 14/16

15. Is the solution to give up on our use of software
for such purposes altogether?!
Introduction
Overview
Safety -Critical Systems
Safety -Critical Systems
Applications, Characteristics, Recent decades bear testimony to how we have gone from
and other Terminologies
merely using software , to rely on it, and to ultimately
Dependability
Taxonomy becoming dependent on it, for our day to day lives.
Threats on Safety -Critical
Systems Dependability Better engineering, testing, and practices are needed to be
Dependability Attributes
implemented, and this is especially true of software that is
Means to Achieve
Dependability related to safety-critical systems.
Achieving Dependability
Quality Attributes Software engineering, and related curriculum at educational
Summary institution should be updated to reflect the every growing
importance of software safety as a field.
Saleh Al-Da’ajeh Safety-Critical Systems Dependability December 23, 2012 15/16

16. Thank you all for attending this seminar.
Questions are most welcomed !