1. Software Engineering Modern Approaches Eric Braude and Michael Bernstein 1

2. © 2010 John Wiley & Sons Ltd. Chapter 13 Quality in Requirements Analysis 2

3. Learning Goals of This Chapter What is meant by the accessibility of requirements? Comprehensiveness? Understandability? How do you assess the degree of ambiguity of requirements? Consistency? Prioritization? What is meant by the degree of security in requirements? In what sense can requirements be complete? Testabile? Traceable? What are suitable metrics for these qualities? Requirements analysis Design Implementation Testing Maintenance Planning The Software Development Lifecycle Phase most relevant to this chapter is shown in bold 3

4. © 2010 John Wiley & Sons Ltd. The Qualities of Requirements Analysis.. accessible is each requirement?.. comprehensive is the SRS?.. understandable is each requirement?.. unambiguous is each requirement?.. consistent is the SRS?.. effectively prioritized are the requirements?.. secure is the requirement?.. self-complete is the SRS?.. testable is each requirement?.. traceable is each requirement? How.. 4

5. © 2010 John Wiley & Sons Ltd. Accessibility Ease of getting to statement of detailed requirements. Metric: 0: extremely long average access time (compared with organization’s norm) 10: average access time as fast as can be expected 5

6. © 2010 John Wiley & Sons Ltd. Issues in Attaining Comprehensive Requirements Not enough resources to satisfy every customer wish – Prioritize so that comprehensive within each batch of requirements Customer can’t / won’t read entire SRS – Make SRS easy to follow – Use a standard – “Read” SRS to customer Limitations of self-inspections – Subject to peer inspection Contradictory stakeholder requirements need to be satisfied – Apply diplomatic skills and expect compromise 6

7. Including Future Requirements Requirement #descriptionPriorityIteration 780Every DVD record shall contain the title, up to 60 alphanumeric characters 23 781Every customer record shall include his credit card number, consisting of 16 digits. 12 782… © 2010 John Wiley & Sons Ltd. 7

8. Comprehensiveness Metrics Let T = total number of documented detailed requirements (all priorities; all iterations) METRIC: % Requirements implemented = 100 * [ # requirements implemented ] T METRIC: % Requirements Currently Targeted = 100 * [ (# requirements implemented) + (# top priority requirements in current iteration) ] T 8

9.  Better version: Whenever all foreign players are absent from the area containing the player's main character, the player may change the quality values of this character, keeping the sum total of the quality values unchanged. The PlayerQualityWindow, (see section tbd) is used for this purpose. Changes take effect four seconds after the “OK” button is pressed. The player can decide the qualities of Encounter characters.  At any time? Probably not. Would have to test under all circumstances, many not intended, incurring unnecessary expense, and producing a wrong result. Ambiguity

10. © 2010 John Wiley & Sons Ltd. A metric (range: 0 to 100) 100 *  [unambiguity of each detailed requirement (0-2)] ________________________________________________ 2 * [number of detailed requirements] 0 = could have many meanings; 2 = clearly one meaning Unambiguity 10

11. Requirement 14. Only basic food staples shall be carried by game characters... Requirement 223. Every game character shall carry water.... Requirement 497. Flour, butter, milk and salt shall be considered the only basic food staples. Example of Inconsistency © 2010 John Wiley & Sons Ltd. 11

12. © 2010 John Wiley & Sons Ltd. Consistency Means: No contradiction, in whole or in part. Example: ….. DVD’s shall be classified alphabetically as drama, comedy, horror ….. Metric: Percentage of contradicted requirements ….. The DVD classification order shall be the order of preference of the customer’s. … 12

13. © 2010 John Wiley & Sons Ltd. A Prioritization Metric Assume three prioritizations: high, medium, and low Metric: Variation from # high = # medium = # low Let T = total number of detailed requirements 100*[ T - | T/3 – # high | - | T/3 - # medium | - | T/3 – # low | ] T 0 = worst; 100 = best 13

14. REQUIREMENTS 1. The application shall display a DVD in stock when a title is entered at the prompt; otherwise it shall display “OUT OF STOCK.” 2. The application shall display all of the store’s DVD’s by any director whose last name is entered at the prompt. These shall be displayed one by one. Advancing through the DVD’s shall be controlled by the forward arrow key. Incomplete : Lacks specification on how to display a video! Self-Completeness: (“nothing else needed” ) 14 © 2010 John Wiley & Sons Ltd.

15. When a requirement is present, so must all those necessitated by its presence. A metric (0 = best; 1 poor; no theoretical upper limit) : [number of missing necessary associated requirements] [number of detailed requirements present] Self-Completeness 15

16. The system shall display the difference in salary between the client and the world wide average for the same trade  -- can't be tested because the average mentioned cannot be determined (event though it exists).  Better: The system shall display the difference in salary between the client and the estimated world-wide average for the same trade as published by the United Nations on its website www.tbd at the time of the display.... www.tbd Testability © 2010 John Wiley & Sons Ltd. 16

17. Example of a User Satisfaction Questionnaire User Satisfaction 0 = of no value; 5 = average satisfaction; 10 = a pleasure to use QualityScore 1. Overall appearance 2. Layout of text areas 3. Layout of buttons 4. Readability 5. Ease of entering data 6. Degree to which erroneous data entry is prevented ….. © 2010 John Wiley & Sons Ltd. 17

18. Including Tests with Requirements: Example Requirement The the video store application shall implement a discount program as follows. One DVD: no discount Two DVD’s: 20% discount for the second DVD Three DVD’s: 40% discount for the second and third DVD All video’s beyond the third are discounted at 40%. © 2010 John Wiley & Sons Ltd. 18

19. Including Tests with Requirements Accompanying Tests 1.Customer Owen Jones rents one DVD. He is charged the regular rental of $5.00 2.Customer Teresa Edwards rents two DVD’s. She is charged the regular rental of $5.00 for the first and $4.00 (20% discount) for the second. 3.Customer Theodore List rents three DVD’s. He is charged the regular rental of $5.00 for the first, $4.00 (20% discount) for the second, and $3.00 (40% discount) for the third. 4. Customer Fred Harari rents five DVD’s. He is charged the regular rental of $5.00 for the first, $4.00 (20% discount) for the second, and $3.00 (40% discount) for the third. The fourth and fifth DVD’s are charged at $3.00 (40% discount). © 2010 John Wiley & Sons Ltd. 19

20. © 2010 John Wiley & Sons Ltd. (Range: 0 to 100) 100 *  [traceability of each detailed requirement (0-2)] ________________________________________________ 2 * [number of detailed requirements] 0 = untraceable; 2 = clearly traceable to a specific class A Traceability Metric 20

21. Example: Form for Detailed Inspection No.Requirement Description Trace- able back- ward Com- prehensive Con- sistent Feasible Unam- biguous ClearPrecise Modifi- able Test- able Traceable forward Note 14 1001 Area Requirement 1 Note 2 Note 1 Yes No 1YesNo 1No 2No 1, 2 Yes 1002 Area Requirement 2 Yes No 3YesNo 3Note 3Yes 1003 Area Requirement 6 YesNote 5 YesNo 3 No 5Yes 1004 Area Requirement 3 Yes Note 6Note 3Yes 1005 Area Requirement 4 YesNote 7Yes 1006 Engagement Requirement 1 Note 2Yes Note 3Yes 1007 EncounterCharacter Requirement 1 YesNote 1Yes No 1YesNo 1No 2No 1, 2 Yes 1008 EncounterCharacter Requirement 2 YesNo 11Yes Note 8YesNo 6YesNote 9 1009 EncounterCharacter Requirement 3 Yes Note 3Yes 1010 EncounterCharacter Requir-ement 4 Note 11 Yes Note 12 No 7Yes 1011 EncounterGame Requirement 1 Yes Note 13Yes 1012 Foreign Character Requirement 1 Note 11 Yes No 8, 9Yes 1013 Player Character Requirement 1 Yes No 10YesNote 15Yes 1014 Player Character Requirement 2 Yes No 12 Note 3No 12Yes 1015 Player Character Requirement 3 Yes Note 10 Yes No.Requirement Description Trace- able back- ward Com- prehensive Con- sistent Feasible Unam- biguous ClearPrecise Modifi- able Test- able Traceable forward Note 14 © 2010 John Wiley & Sons Ltd. 21