1. CS540 Software Design Lecture 6 & 7 1 Lecture 6 & 7: Structured Analysis Anita S. Malik anitamalik@umt.edu.pk Adapted from Schach (2004) Chapter 11

2. CS540 Software Design 2Lecture 6 & 7 Specifications Phase Specification document must be Specification document must be Informal enough for client Informal enough for client Formal enough for developers Formal enough for developers Free of omissions, contradictions, ambiguities Free of omissions, contradictions, ambiguities Specification techniques include Specification techniques include Informal specifications Informal specifications Structured systems analysis Structured systems analysis Object Oriented analysis Object Oriented analysis Entity-relationship modeling Entity-relationship modeling Finite state machines Finite state machines Petri nets Petri nets Other formal techniques such as Z specification Other formal techniques such as Z specification

3. CS540 Software Design 3Lecture 6 & 7 Informal Specifications Example Example “If sales for current month are below target sales, then report is to be printed, unless difference between target sales and actual sales is less than half of difference between target sales and actual sales in previous month, or if difference between target sales and actual sales for the current month is under 5%”

4. CS540 Software Design 4Lecture 6 & 7 Meaning of Specification Sales target for January was $100,000, actual sales were only $64,000 (36% below target) Sales target for January was $100,000, actual sales were only $64,000 (36% below target) Print report Print report Sales target for February was $120,000, actual sales were only $100,000 (16.7% below target) Sales target for February was $120,000, actual sales were only $100,000 (16.7% below target) Percentage difference for February (16.7%) less than half of previous month’s percentage difference (36%), do not print report Percentage difference for February (16.7%) less than half of previous month’s percentage difference (36%), do not print report Sales target for March was $100,000, actual sales were $98,000 (2% below target) Sales target for March was $100,000, actual sales were $98,000 (2% below target) Percentage difference < 5%, do not print Percentage difference < 5%, do not print

5. CS540 Software Design 5Lecture 6 & 7 But Specifications Do Not Say This “[D]ifference between target sales and actual sales” “[D]ifference between target sales and actual sales” There is no mention of percentage difference There is no mention of percentage difference Difference in January was $36,000, difference in February was $20,000 Difference in January was $36,000, difference in February was $20,000 Not less than half of $36,000, so report is printed Not less than half of $36,000, so report is printed “[D]ifference … [of] 5%” “[D]ifference … [of] 5%” Again, no mention of percentage Again, no mention of percentage Ambiguity—should the last clause read “percentage difference … [of] 5%” or “difference … [of] $5,000” or something else entirely? Ambiguity—should the last clause read “percentage difference … [of] 5%” or “difference … [of] $5,000” or something else entirely? Style is poor Style is poor

6. CS540 Software Design 6Lecture 6 & 7 Informal Specifications (contd) Claim Claim This cannot arise with professional specifications writers This cannot arise with professional specifications writers Refutation Refutation Text Processing case study Text Processing case study

7. CS540 Software Design 7Lecture 6 & 7 Episode 1 1969 — Naur Paper 1969 — Naur Paper Given a text consisting of words separated by blank or by nl (new line) characters, convert it to line-by-line form in accordance with following rules: (1) line breaks must be made only where given text has blank or nl ; (2)each line is filled as far as possible, as long as (3)no line will contain more than maxpos characters Naur constructed a procedure (25 lines of Algol 60), and informally proved its correctness) Naur constructed a procedure (25 lines of Algol 60), and informally proved its correctness)

8. CS540 Software Design 8Lecture 6 & 7 Episode 2 1970 — Reviewer in Computing Reviews 1970 — Reviewer in Computing Reviews First word of first line is preceded by a blank unless the first word is exactly maxpos characters long First word of first line is preceded by a blank unless the first word is exactly maxpos characters long

9. CS540 Software Design 9Lecture 6 & 7 Episode 3 1971 — London found 3 more faults 1971 — London found 3 more faults Including: procedure does not terminate unless a word longer than maxpos characters is encountered Including: procedure does not terminate unless a word longer than maxpos characters is encountered

10. CS540 Software Design 10Lecture 6 & 7 Episode 4 1975 — Goodenough and Gerhart found 3 further faults 1975 — Goodenough and Gerhart found 3 further faults Including—last word will not be output unless it is followed by blank or nl Including—last word will not be output unless it is followed by blank or nl Goodenough and Gerhart then produced new set of specifications, about four times longer than Naur’s Goodenough and Gerhart then produced new set of specifications, about four times longer than Naur’s

11. CS540 Software Design 11Lecture 6 & 7 Case Study (contd) 1985 — Meyer detected 12 faults in Goodenough and Gerhart’s specifications 1985 — Meyer detected 12 faults in Goodenough and Gerhart’s specifications Goodenough and Gerhart’s specifications Goodenough and Gerhart’s specifications Were constructed with the greatest of care Were constructed with the greatest of care Were constructed to correct Naur’s specifications Were constructed to correct Naur’s specifications Went through two versions, carefully refereed Went through two versions, carefully refereed Were written by experts in specifications Were written by experts in specifications With as much time as they needed With as much time as they needed For a product about 30 lines long For a product about 30 lines long What chance do we have of writing fault-free specifications for a real product? What chance do we have of writing fault-free specifications for a real product?

12. CS540 Software Design 12Lecture 6 & 7 Episode 5 1989 — Schach found fault in Meyer’s specifications 1989 — Schach found fault in Meyer’s specifications Item (2) of Naur’s original requirement (“each line is filled as far as possible”) is not satisfied Item (2) of Naur’s original requirement (“each line is filled as far as possible”) is not satisfied

13. CS540 Software Design 13Lecture 6 & 7 Informal Specifications Conclusion Conclusion Natural language is not a good way to specify product Natural language is not a good way to specify product Fact Fact Many organizations still use natural language, especially for commercial products Many organizations still use natural language, especially for commercial products Reasons Reasons Uninformed management Uninformed management Undertrained computer professionals Undertrained computer professionals Management gives in to client pressure Management gives in to client pressure Management is unwilling to invest in training Management is unwilling to invest in training

14. CS540 Software Design 14Lecture 6 & 7 Structured Systems Analysis Three popular graphical specification methods of ’70s Three popular graphical specification methods of ’70s DeMarco DeMarco Gane and Sarsen Gane and Sarsen Yourdon Yourdon All equivalent All equivalent All equally good All equally good Many corporations use them for commercial products Many corporations use them for commercial products Gane and Sarsen used for object-oriented design Gane and Sarsen used for object-oriented design

15. CS540 Software Design 15Lecture 6 & 7 Structured Systems Analysis Case Study Sally’s Software Store buys software from various suppliers and sells it to the public. Popular software packages are kept in stock, but the rest must be ordered as required. Institutions and corporations are given credit facilities, as are some members of the public. Sally’s Software Store is doing well, with a monthly turnover of 300 packages at an average retail cost of $250 each. Despite her business success, Sally has been advised to computerize. Should she? Better question Better question What sections? What sections? Still better Still better How? Batch, or online? In-house or out-service? How? Batch, or online? In-house or out-service?

16. CS540 Software Design 16Lecture 6 & 7 Case Study (contd) Fundamental issue Fundamental issue What is Sally’s objective in computerizing her business? What is Sally’s objective in computerizing her business? Because she sells software? Because she sells software? She needs an in-house system with sound and light effects She needs an in-house system with sound and light effects Because she uses her business to launder “hot” money? Because she uses her business to launder “hot” money? She needs a product that keeps five different sets of books, and has no audit trail She needs a product that keeps five different sets of books, and has no audit trail Assume: Computerization “in order to make more money” Assume: Computerization “in order to make more money” Cost/benefit analysis for each section of business Cost/benefit analysis for each section of business

17. CS540 Software Design 17Lecture 6 & 7 Case Study (contd) The danger of many standard approaches The danger of many standard approaches First produce the solution, then find out what the problem is! First produce the solution, then find out what the problem is! Gane and Sarsen’s method Gane and Sarsen’s method Nine-step method Nine-step method Stepwise refinement is used in many steps Stepwise refinement is used in many steps

18. CS540 Software Design 18Lecture 6 & 7 Case Study (contd) Data flow diagram (DFD) shows logical data flow Data flow diagram (DFD) shows logical data flow “what happens, not how it happens” “what happens, not how it happens”

19. CS540 Software Design 19Lecture 6 & 7 Step 1. Draw the DFD First refinement First refinement Infinite number of possible interpretations Infinite number of possible interpretations

20. CS540 Software Design 20Lecture 6 & 7 Step 1 (contd) Second refinement Second refinement pending orders scanned daily pending orders scanned daily

21. CS540 Software Design 21Lecture 6 & 7 Step 1 (contd) Portion of third refinement Portion of third refinement

22. CS540 Software Design 22Lecture 6 & 7 Step 1 (contd) Final DFD Final DFD Larger, But easily understood by client Larger, But easily understood by client Larger DFDs Larger DFDs Hierarchy Hierarchy Box becomes DFD at lower level Box becomes DFD at lower level Frequent problem Frequent problem Process P at level L, expanded at level L+1 Process P at level L, expanded at level L+1 Correct place for sources and destinations of data for process P is level L+1 Correct place for sources and destinations of data for process P is level L+1 Clients cannot understand DFD—sources and destinations of data for P are “missing” Clients cannot understand DFD—sources and destinations of data for P are “missing” Solution Solution Draw “correct” DFD, modify by moving sources and destinations of data one or more levels up Draw “correct” DFD, modify by moving sources and destinations of data one or more levels up

23. CS540 Software Design 23Lecture 6 & 7 Step 2. Decide What Parts to Computerize Depends on how much client is prepared to spend Depends on how much client is prepared to spend Large volumes, tight controls Large volumes, tight controls Batch Batch Small volumes, in-house microcomputer Small volumes, in-house microcomputer Online Online Cost/benefit analysis Cost/benefit analysis

24. CS540 Software Design 24Lecture 6 & 7 Step 3. Refine Data Flows Data items for each data flow Data items for each data flow Refine each flow stepwise Refine each flow stepwise Refine further Refine further Need a data dictionary Need a data dictionary

25. CS540 Software Design 25Lecture 6 & 7 Step 3. Refine Data Flows (contd) Sample data dictionary entries Sample data dictionary entries

26. CS540 Software Design 26Lecture 6 & 7 Step 4. Refine Logic of Processes Have process give educational discount Have process give educational discount Sally must explain discount for educational institutions Sally must explain discount for educational institutions 10% on up to 4 packages, 15% on 5 or more 10% on up to 4 packages, 15% on 5 or more Translate into decision tree Translate into decision tree

27. CS540 Software Design 27Lecture 6 & 7 Step 4 (contd) Advantage of decision tree Advantage of decision tree Missing items are quickly apparent Missing items are quickly apparent Can also use decision tables Can also use decision tables CASE tools for automatic translation CASE tools for automatic translation

28. CS540 Software Design 28Lecture 6 & 7 Step 5. Refine Data Stores Define exact contents and representation (format) Define exact contents and representation (format) COBOL: specify to pic level COBOL: specify to pic level Ada: specify digits or delta Ada: specify digits or delta Specify where immediate access is required Specify where immediate access is required Data immediate access diagram (DIAD) Data immediate access diagram (DIAD)

29. CS540 Software Design 29Lecture 6 & 7 Step 6. Define Physical Resources For each file, specify For each file, specify File name File name Organization (sequential, indexed, etc.) Organization (sequential, indexed, etc.) Storage medium Storage medium Blocking factor Blocking factor Records (to field level) Records (to field level)

30. CS540 Software Design 30Lecture 6 & 7 Step 7. Determine Input/Output Specs Specify input forms, input screens, printed output Specify input forms, input screens, printed output

31. CS540 Software Design 31Lecture 6 & 7 Step 8. Perform Sizing Numerical data for Step 9 to determine hardware requirements Numerical data for Step 9 to determine hardware requirements Volume of input (daily or hourly) Volume of input (daily or hourly) Size, frequency, deadline of each printed report Size, frequency, deadline of each printed report Size, number of records passing between CPU and mass storage Size, number of records passing between CPU and mass storage Size of each file Size of each file

32. CS540 Software Design 32Lecture 6 & 7 Step 9. Hardware Requirements DASD requirements DASD requirements Mass storage for back-up Mass storage for back-up Input needs Input needs Output devices Output devices Is existing hardware adequate? Is existing hardware adequate? If not, recommend buy/lease If not, recommend buy/lease

33. CS540 Software Design 33Lecture 6 & 7 However Response times cannot be determined Response times cannot be determined Number of I/O channels can only be guessed Number of I/O channels can only be guessed CPU size and timing can only be guessed CPU size and timing can only be guessed Nevertheless, no other method provides these data for arbitrary products Nevertheless, no other method provides these data for arbitrary products The method of Gane and Sarsen/De Marco/Yourdon has resulted in major improvements in the software industry The method of Gane and Sarsen/De Marco/Yourdon has resulted in major improvements in the software industry

34. CS540 Software Design 34Lecture 6 & 7 Structured Analysis (Summary) Nine Steps: 1. Draw the Data Flow Diagram (DFD) 2. Decide what section to computerize 3. Determine the details of the data flows 4. Define the logic of the processes 5. Define the data stores 6. Define the physical resources 7. Determine input-output specifications 8. Perform sizing 9. Determine the hardware requirements

35. CS540 Software Design 35Lecture 6 & 7 Air Gourmet Case Study: Structured Sys. Anal. Data flow diagram reflects centrality of SPECIAL MEAL DATA Data flow diagram reflects centrality of SPECIAL MEAL DATA See Appendix E for remainder of structured systems analysis See Appendix E for remainder of structured systems analysis

36. CS540 Software Design 36Lecture 6 & 7 Testing during the Specification Phase Walkthrough of the document Walkthrough of the document Inspect the document against a checklist. A study done on inspections showed each hour invested in inspections at analysis stage saved 30 hrs of execution-based fault detection and correction. Inspect the document against a checklist. A study done on inspections showed each hour invested in inspections at analysis stage saved 30 hrs of execution-based fault detection and correction.

37. CS540 Software Design 37Lecture 6 & 7 Metrics for Analysis Phase Size, cost, duration, effort and quality Size, cost, duration, effort and quality Size: number of pages in the specification document Size: number of pages in the specification document Quality: note the number of faults of each type found during inspection Quality: note the number of faults of each type found during inspection Duration and effort: number of items in the data dictionary, number of files, data items, processes etc. Duration and effort: number of items in the data dictionary, number of files, data items, processes etc.

38. CS540 Software Design 38Lecture 6 & 7 Challenges of Analysis Phase The documents generated during the analysis phase should be informal enough for the client to understand and formal enough for the development team to use as the description of the product to be built The documents generated during the analysis phase should be informal enough for the client to understand and formal enough for the development team to use as the description of the product to be built To keep within the ‘what’ boundary and not cross to the ‘how’ boundary To keep within the ‘what’ boundary and not cross to the ‘how’ boundary