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Software Architecture Case Study: A-7E Project Insights and Decomposition Strategies

This case study presents an in-depth examination of the A-7E project, highlighting its historical context, software architecture principles, and decomposition strategies. It draws on insights from "Software Architecture in Practice" and focuses on key aspects like information hiding and the structure of modules. Key project features such as avionics integration, data types, and process structures are explored. Additionally, the study emphasizes the importance of separation of concerns to enhance maintainability and adaptability in software systems.

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Software Architecture Case Study: A-7E Project Insights and Decomposition Strategies

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  1. A-7E Case Study CSSE 477 Software ArchitectureSteve Chenoweth, Rose-Hulman InstituteWk 1, Day 3

  2. Today • A case history – this • Ch 3 in Bass, et al. • Time to work on Project 1 in class.

  3. A7E - Acknowledgements Some of the material in these slides is taken from Software Architecture in Practice, 2nd edition by Bass, Clements, Kazman. http://www.sei.cmu.edu/staff/ljb/, http://www.sei.cmu.edu/staff/clements/, http://www.sei.cmu.edu/staff/rkazman/.

  4. Outline • History of A-7E Project • Decomposition Structure • Uses Relation • Process Structure

  5. David Parnas David Weiss Paul Clements Kathryn Britton Naval Research Laboratory

  6. A-7E History • Software Cost Reduction (SCR) • Information hiding • A-7E Project (1977 - 1987) • Requirements discovery • Reference Architecture • Software Architecture and Design • Partial implementation

  7. A-7E Avionics • Sensors • air probe • radar • Displays • map • heads-up • Input • joystick • keypad

  8. Module Guide • Provides decomposition structure of software architecture • Describes information hiding modules • Purposes: • avoid duplication and gaps • achieve separation of concerns • help maintainer find modules affected by a change request

  9. Decomposition Goals • Each module should be simple enough to understand fully • Change in implementation of a module should not affect other modules • Ease of making change related to likelihood of need for change

  10. Decomposition Structure • Hardware-Hiding Module • Behavior-Hiding Module • Software Decision Module • Application Data Type Module • Data Banker Module • Filter Behavior Module • Physical Models Module • Software Utility Module • System Generation Module

  11. Uses Relation • Similar to "calls" relation • Layers of what can call what: • EC = Extended Computer at the bottom • AT = Application Data Type Module • DI = Device Interface Module • FD = Function Driver Module • SS = Shared Services Module • Allowed-to-use relation defined in advance to partition programming These two at the top

  12. Layers Implied by Uses Relation

  13. Process Structure • Cooperating Sequential Processes • synchronization via shared data • Types of processes: • Function driver processes (for avionics): • Periodic – run every 40 ms • Demand-driven – await a triggering event • Access procedure processes (less frequent): • Periodic – run every 100 ms – compute and store values • Procedures to get and use values when called • Offline scheduling – to run all this on single processor! Avoids scheduling decisions at runtime.

  14. Process Consequences The offline analysis possible from the process design let lots of scheduling be pre-determined (prior to runtime): • Thread structure identified • Re-entrant procedures identified • Most-often invoked procedures identified • Mutual exclusion identified

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