SafetyCritical Systems 6 Quality Management and Certification

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Safety-Critical Systems 6Quality Management and
Certification

• T 79.5303

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Quality Management

• Systematic actions to gain quality,which is
  essential in the life cycle of a safety system.
• Quality Assurance
• - concentrates that manufacture prosess and
  work are performed correctly.
• Quality Control
• - ensures that product is correct.

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ISO 9000Quality Management System

• International Organisation for Standardisation
  (ISO) created the Quality Management System (QMS)
  basis already in 1987.
• ISO 90011987 Model for quality assurance in
  design, development, production, installation and
  servicing.
• ISO 90021987 Model for quality assurance in
  production, installation and servicing.
• ISO 90031987 Model for quality assurance in
  final inspection and test covered only the final
  inspection of finished product.

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ISO 9001

• ISO 90002000 combines the three standards 9001,
  9002, and 9003 into one, now called 9001.
• Design and development procedures are required
  only if a company does in fact engage in the
  creation of new products.
• New version has a goal to improve effectiveness
  via process performance metrics numerical
  measurement of the effectiveness of tasks and
  activities.

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ISO 9001

• A company or organization that has been
  independently audited and certified to be in
  conformance with ISO 9001 may publicly state that
  it is "ISO 9001 certified" or "ISO 9001
  registered."
• Certification to an ISO 9000 standard does not
  guarantee the compliance (and therefore the
  quality) of end products and services rather, it
  certifies that consistent business processes are
  being applied.
• ISO 9001 is not enough and more strict systems
  are needed. These are described on norms, which
  have to be followed according to get system
  certificated.

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ISO 9001 System

• The requirements in ISO 9001 include
• a set of procedures that cover all key processes
  in the business
• monitoring manufacturing processes to ensure
  manufactures are producing quality produce
• keeping proper records
• checking outgoing product for defects, with
  appropriate corrective action where necessary
• regularly reviewing individual processes and the
  quality system itself for effectiveness.

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Certification

• Process to indicate conformance with a standard
  checked by an authorised body.
• National Safety Authority, Minister of
  Transportation
• International institutes and certified /notified
  bodies in EU
• Follow given guidelines, like DO-178B, IEC 61508
  or CENELEC norms.

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Example in Avionic systemDO-178B Certification

• DO-178B provides the aviation community with
  guidelines for developing software for airborne
  systems and equipment that complies with accepted
  airworthiness requirements.
• Five software levels (A through E), Level A is
  the most stringent.

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DO-178B Certification
The number of objectives to be satisfied. In the
standard, "with independence" refers to a
separation of responsibilities where the
person(s) who verify an objective must not be the
developers of the item in question. In some
cases, an automated tool may be equivalent to
independence.
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Safety-Critical Systems Summary

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V - Lifecycle model
Requirements Model
Requirements Analysis
Test Scenarios
Test Scenarios
System Acceptance
Requirements Document
Functional / Architechural - Model
System Integration Test
Systems Analysis Design
Specification Document
Software Design
Module Integration Test
Software Implementation Unit Test
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I - Requirements

• Requirements are stakeholders (customer) demands
  what they want the system to do.
• Not defining how !!! gt specification
• Safety requirements are defining what the system
  must do and must not do in order to ensure
  safety. Both positive and negative functionality.
•  

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I - Requirement Engineering Right Requirements

• Ways to refine Requirements
• - complete linking to hazards (possible
  dangerous events)
• - correct testing modelling
• - consistent semi/formal language
• - unambiguous text in real English
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I - Semi-formal Requirements

• Requirements should be inambigious, complete,
  consistent and correct.
• Natural language has the intepretation
  possibility. More accurate description needed.
• Using pure mathematic notation not always
  suitable for communication with domain expert.
• Formalised Methods are used to tackle the
  requirement engineering. (Structured text,
  formalised English).

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I - Hazard formalisation
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I Multiple Hazards
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I - Hazard example
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I - Hazard Analysis

• A Hazard is situation in which there is actual or
  potential danger to people or to environment.
• Analytical techniques
• - Failure modes and effects analysis (FMEA)
• - Failure modes, effects and criticality
  analysis (FMECA)
• - Hazard and operability studies (HAZOP)
• - Event tree analysis (ETA)
• - Fault tree analysis (FTA)

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Fault Tree Analysis 1
The diagram shows a heater controller for a tank
of toxic liquid. The computer controls the heater
using a power switch on the basis of information
obtained from a temperature sensor. The sensor is
connected to the computer via an electronic
interface that supplies a binary signal
indicating when the liquid is up to its required
temperature. The top event of the fault tree is
the liquid being heated above its required
temperature.
 
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Fault event not fully traced to its source
Basic event, input
Fault event resulting from other events
OR connection
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I - Risk Analysis

• Risk is a combination of the severity (class) and
  frequency (probability) of the hazardous event.
• Risk Analysis is a process of evaluating the
  probability of hazardous events.
• The Value of life??
• Value of life is estimated between 0.75M 2M
  GBP.
• USA numbers higher.

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V - Lifecycle model
Requirements Model
Requirements Analysis
Test Scenarios
Test Scenarios
System Acceptance
Requirements Document
Functional / Architechural - Model
System Integration Test
Systems Analysis Design
Specification Document
Software Design
Module Integration Test
Software Implementation Unit Test
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II - Designing for Safety 1

• Faults groups
• - requirement/specification errors
• - random component failures
• - systematic faults in design (software)
• Approaches to tackle problems
• - right system architecture (fault-tolerant)
• - reliability engineering (component, system)
• - quality management (designing and producing
  processes)

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II - Designing for Safety 2

• Hierarchical design
• - simple modules, encapsulated functionality
• - separated safety kernel safety critical
  functions
• Maintainability
• - preventative versa corrective maintenance
• - scheduled maintenance routines for whole
  lifecycle
• - easy to find faults and repair short MTTR
  mean time to repair
• Human error
• - Proper HMI

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II Design - Fault Tolerance

• Fault tolerance hardware- Achieved mainly by
  redundancy Redundancy- Adds cost, weight, power
  consumption, complexityOther means- Improved
  maintenance, single system with better materials
  (higher MTBF)

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V - Lifecycle model
Requirements Model
Requirements Analysis
Test Scenarios
Test Scenarios
System Acceptance
Requirements Document
Functional / Architechural - Model
System Integration Test
Systems Analysis Design
Specification Document
Software Design
Module Integration Test
Software Implementation Unit Test
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III - Safety-Critical Software 1

• Correct Program
• Normally iteration is needed to develop a
  working solution. (writing code, testing and
  modification).
• In non-critical environment code is accepted,
  when tests are passed.
• Testing is not enough for safety-critical
  application Needs an assessment process
  dynamic/static testing, simulation, code analysis
  and formal verification.

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III - Safety-Critical Software 2

• Dependable Software
• Process for development
• Work discipline
• Well documented
• Quality management
• Validated/verificated

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III - Safety-Critical Software 3

• Designing Principles
• Use hardware interlocks before computer/software
  
• New software features add complexity, try to
  keep software simple
• Plan for avoiding human error unambigious
  human-computer interface
• Removal of hazardous module (Ariane 5 unused
  code)

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III - Safety-Critical Software 4

• Designing Principles
• Add barriers hard/software locks for critical
  parts
• Minimise single point failures increase safety
  margins, exploit redundancy and allow recovery.
• Isolate failures dont let things get worse.
• Fail-safe panic shut-downs, watchdog code
• Avoid common mode failures Use diversity
  different programmers, n-version programming

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III - Safety-Critical Software 5

• Designing Principles
• Fault tolerance Recovery blocks if one module
  fails, execute alternative module.
• Dont relay on run-time systems

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III - Safety-Critical Software 6

• Reduction of Hazardous Conditions -summary
• Simplify Code contains only minimum features
  and no unnecessary or undocumented features or
  unused executable code
• Diversity Data and control redundancy
• Multi-version programming shared specification
  leads to common-mode failures, but
  synchronisation code increases complexity

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Verified software process
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V - Lifecycle model
Requirements Model
Requirements Analysis
Test Scenarios
Test Scenarios
System Acceptance
Requirements Document
Functional / Architechural - Model
System Integration Test
Systems Analysis Design
Specification Document
Software Design
Module Integration Test
Software Implementation Unit Test
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Testing

• Testing is a process used to verify or validate
  system or its components.
• Testing is performed during various stage of
  system development. V-lifecycle diagram.
• Module testing evaluation of a small function
  of the hardware/software.
• System integration testing investigates
  correct interaction of modules.
• System validation testing a complete system
  satisfies its requirements.

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Home assignments

• 1.12 (primary, functional and indirect safety)
• 2.4 (unavailability)
• 5.10 (incompleteness within specification)
• 7.15 (reliability model)
• 9.17 (reuse of software)
• 11.2 Textual specification
• 11.18 Z-language
• 12.7 Dynamic testing
• Please email your home assignments by 26 April
  2007 to herttua_at_uic.asso.fr
• References OFFIS, I-Logix, KnowGravity