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Project Management: Inspections and Reviews Formal Specifications

Project Management: Inspections and Reviews Formal Specifications. 5 February. Deliverables. Design Document Only highest levels Details will be filled in Living document. Reviews and Inspections. Reviews and Inspections. Why? Developer can’t correct unseen errors

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Project Management: Inspections and Reviews Formal Specifications

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  1. Project Management:Inspections and ReviewsFormal Specifications 5 February

  2. Deliverables • Design Document • Only highest levels • Details will be filled in • Living document

  3. Reviews and Inspections

  4. Reviews and Inspections • Why? • Developer can’t correct unseen errors • More eyes to catch problems • Earlier is cheaper • Integration fix typically 3-10 times the cost at design • Difference in terms • Review implies completed work, often reviewed by someone at a different level • Inspection implies peer review of work in progress

  5. Software Inspections • Disciplined engineering practice for detecting and correcting defects • Introduced at IBM by Fagan in the 1970s • More formal than walkthroughs or peer reviews • Roles, statistics • Used for specs, code, test plans, …

  6. Uses • Early detection of errors • Major escapes cost 2-10 times as much; minor 2-4 • Identification of excellence indicators • Completeness (requirements to code) • Correctness (specification to code) • Style (consistency) • Exit criteria for life cycle phases

  7. Additional Benefits • Programmer finds errors and types of errors that he is apt to make immediately • Awareness means focus on those types of errors and therefore improved skills • Designers get feedback on quality of their designs • Using statistical anomalies to recode

  8. Why do inspections work? • More eyes • Focused activity • Structure • Timely • Measurable criteria for passing and rework • Required follow-up

  9. Why Aren’t Inspections Used? • Rigorous and formal (requires training) • Time consuming • 4-5 people over multiple 2 hour sessions • 250-500 lines of code per hour • 5-10 errors detected per session • Boring, low tech • Egos

  10. References • Fagan, Design and code inspections to reduce errors in program development, IBM Systems Journal (reprinted 99) • Porter, Siy and Votta, A Review of Software Inspections, 1995

  11. Will you review or inspect?What?How?

  12. Formal Specifications

  13. Formal Methods and Specifications • Mathematically-based techniques for describing system properties • Used to show completeness, consistency, unambiguity • Able to be used without executing the program (inference systems)

  14. Inference Systems • Proving something about the specification not already stated • Formal proofs • Mechanizable • Examples: theorem provers and proof checkers

  15. Users of Specifications • Requirements analysis • rigor • System design • Decomposition, interfaces • Verification • Specific sections • Documentation • System analysis and evaluation • Reference point, uncovering bugs

  16. Properties of Specifications • Unambiguous • Maps to a single specificand set • Consistency • Maps to a non-empty specificand set • Completeness • Not required! • Balance between underspecification and overspecification

  17. Examples of Specification Languages • Abstract data types • Algebras, theories, and programs • VDM (Praxis: UK Civil aviation display system CDIS), Z (Oxford and IBM: CICS), Larch (MIT) • Concurrent and distributed systems • State or event sequences, transitions • Hoare’s CSP, Transition axioms, Lamport’s Temporal Logic • Programming languages!

  18. References • J.M. Wing, A Specifier's Introduction to Formal Methods. IEEE Computer, 23(9):8-24, September 1990. • Clarke et al, Formal methods: state of the art and future directions, ACM Computing Surveys, 28(4): 626--643, 1996.

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