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Stepwise Refinement in Software Engineering

Learn about stepwise refinement in software engineering, its principles, benefits, and a mini case study demonstrating its application in designing a product. Understand how to concentrate on important issues and postpone detailed decisions. Explore the power of stepwise refinement and its impact on software development.

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Stepwise Refinement in Software Engineering

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  1. Object-Oriented and Classical Software EngineeringSixth Edition, WCB/McGraw-Hill, 2005Stephen R. Schachsrs@vuse.vanderbilt.edu

  2. CHAPTER 5 — Unit A THE TOOLS OF THE TRADE

  3. Overview • Stepwise refinement • Cost–benefit analysis • Software metrics • CASE • Taxonomy of CASE • Scope of CASE • Software versions • Configuration control • Build tools • Productivity gains with CASE technology

  4. 5.1 Stepwise Refinement • A basic principle underlying many software engineering techniques • “Postpone decisions as to details as late as possible to be able to concentrate on the important issues” • Miller’s law (1956) • A human being can concentrate on 7 ± 2 items at a time

  5. 5.1.1 Stepwise Refinement Mini Case Study • Design a product to update a sequential master file containing name and address data for the monthly magazine True Life Software Disasters • Three types of transactions • Type 1: INSERT (a new subscriber into the master file) • Type 2: MODIFY (an existing subscriber record) • Type 3: DELETE (an existing subscriber record) • Transactions are sorted into alphabetical order, and by transaction code within alphabetical order

  6. Typical File of Input Transactions Figure 5.1

  7. Decompose Process • No further refinement is possible Figure 5.2

  8. First Refinement Figure 5.3

  9. Stepwise Refinement Case Study (contd) • Assumption • We can produce a record when PROCESS requires it • Separate INPUT and OUTPUT, concentrate on PROCESS

  10. Stepwise Refinement Case Study (contd) • What is this PROCESS? • Example: Figure 5.4

  11. Stepwise Refinement Case Study (contd) • More formally: Figure 5.5

  12. Second Refinement Figure 5.6

  13. Third Refinement • This design has a major fault Figure 5.7

  14. Stepwise Refinement Case Study (contd) • The third refinement is WRONG • “Modify JONES” followed by “Delete JONES” is incorrectly handled

  15. Stepwise Refinement Case Study (contd) • After the third refinement has been corrected • Details like opening and closing files have been ignored up to now • Fix these after the logic of the design is complete • The stage at which an item is handled is vital • Opening and closing files is • Ignored in early steps, but • Essential later

  16. Appraisal of Stepwise Refinement • A basic principle used in • Every workflow • Every representation • The power of stepwise refinement • The software engineer can concentrate on the relevant aspects • Warning • Miller’s Law is a fundamental restriction on the mental powers of human beings

  17. Continued in Unit 5B

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