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Modular Certification Basic Concepts

Modular Certification Basic Concepts. Overview . Objectives of Incremental Certification Principles Modular GSN Patterns/Templates Product/Process Containment IAWG Modular Software Safety Case Process. Cost of re-certification is related to the size and complexity of the system.

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Modular Certification Basic Concepts

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  1. Modular Certification Basic Concepts 18/04/07

  2. Overview • Objectives of Incremental Certification • Principles • Modular GSN • Patterns/Templates • Product/Process • Containment • IAWG Modular Software Safety Case Process 18/04/07

  3. Cost of re-certification is related to the size and complexity of the system. Cost of re-certification is related to the size and complexity of the change. £ £ Change Size & Complexity Change Size & Complexity Objectives:Typical Cost Relationships for Certification Current Aim for the Future 18/04/07

  4. Principles of Modular Certification • First step towards Incremental Certification is Modular Certification • Apply principles of object orientation to Safety Cases: • High cohesion • Low coupling • Information Hiding • Well-defined interfaces 18/04/07

  5. PublicGoal Module Reference ‘Away’Goal Modular GSN – Basic Symbols 18/04/07

  6. Modular GSN – Module View/Safety Case Architecture 18/04/07

  7. MSL Design Architecture Safety Case Architecture Application Layer (AL) RTBP OSL 18/04/07

  8. Patterns/Templates • Patterns • Authoring-Time Instantiations • Template • Read-Time Instantiations 18/04/07

  9. Product/Process • DEF STAN 00-56 issue 2 requires that process to develop system/software is appropriate • DEF STAN 00-56 issue 3 requires that product is demonstrated to be acceptably safe and only uses process argument where needed to support product evidence • Parallel study undertaken to DEF STAN 00-56 issue 3 • Process acceptability only highlighted where product argument relies upon it – public ‘process’ goal • Public process goal could be supported • Empirically, per instance of dependence on process argument • Generically, as individual public goals within an overall process argument • Variance of process with assurance requirements has not yet been considered 18/04/07

  10. Containment • Safety Case equivalent to ‘information hiding’, to manage complexity in safety case architectures • It is not always necessary for each safety case module to have visibility of all other safety case modules • Where elements of one safety case module are of limited applicability, their scope can be limited through containment • Particularly useful for Process arguments which relate only to a single product argument module 18/04/07

  11. Containment Simplifying the SCAWithout Containment 18/04/07

  12. Containment Simplifying the SCA With Containment 18/04/07

  13. Methods for Modular Certification • Probably many ways to do modular certification • IAWG have investigated modular software safety cases • Further material refers to experience gained in defining the IAWG Modular Software Safety Case method • Start by looking at how to define the Safety Case Architecture 18/04/07

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