THE UNIVERSITY OF WESTERN ONTARIO CS212b: Introduction to Software Engineering Final Examination: Marking Scheme

Transcription

1 THE UNIVERSITY OF WESTERN ONTARIO CS212b: Introduction to Software Engineering Final Examination: Marking Scheme Instructor: Raphael M. Bahati Sunday, April 19, 2005 This is a closed book exam with no reference materials or electronic devices of any type allowed. The exam consists of 8 questions worth a total of 150 marks. The mark allotment is provided for each question. It is recommended that you use the marks as a guide for the amount of time you should spend on each question. There are 20 pages in the exam, including this page. Write all your answers in the booklet provided. A summary sheet of UML notations is also provided. Question Marks Achieved TOTAL 150

2 1. [ 8 marks ] Briefly describe 3 important attributes of software quality. Usability, Efficiency, Reliability, Maintainability, Efficiency, and Reusability. Give 2 marks for each correct answer Give 2 marks for clarity 2. [ 7 marks ] In the class, we discussed two important techniques for verifying that a software performs as required. Which activity should be performed first, testing or inspection? Give a brief justification. Inspection should be performed before testing [ 3 marks ]. Inspection allows you to get rid of many defects quickly. If testing is done before inspection, and the inspectors then recommend that redesign is needed, the testing work has been wasted [ 4 marks ]. Give a maximum of 3 marks if they provided a good explanation to why testing should be done before inspection. 2

3 3. [ 15 marks ] Specify the behavior of a simple alarm clock using UML state diagrams. The alarm consists of three buttons: ALARM: for setting the alarm time SNOOZE: for postponing the ringing of the alarm. ON/OFF: for enabling and disabling the alarm. Initially, the alarm is disabled. Whenever the current time is the same as the alarm time and the alarm is enabled, the alarm starts ringing. If the alarm is ringing and the SNOOZE button is pressed, the ringing is postponed for 10 minutes. The alarm time can be set at any time using the ALARM button. Only when the alarm is enabled can it be disabled using the ON/OFF button. Enabled Not Ringing SNOOZE Disabled ON/OFF [currenttime =alarmtime] Snoozing ON/OFF after(10m) Ringing SNOOZE ALARM Set Alarm Time Deduct 1 mark for each missing state: Disabled, Enabled, Ringing, Not Ringing, and Snoozing. Deduct 1 mark for each missing transition. Deduct 1 mark for missing the start state. 3

4 4. [ 40 marks ] In your project, you were required to develop a software that will allow administrators to manage (add/update/delete) courses, students, and instructors. Instructors could also run the software to manage students grades, while students could use the software to register/drop courses. (a) In class, we identified five software process models: the waterfall model, the phased-release model, the spiral model, the evolutionary model, and the concurrent engineering model. i. Which model fits well with the approach used for the class project? Give a brief justification [ 4 marks ] The waterfall model, the phased release model, and the concurrent engineering model. A key characteristic is non changing requirements. Give 2 marks for identifying the correct model Give 2 marks for giving the correct justification. mention requirements specification. Only give 1 mark if they don t ii. What are the advantages of adopting the model you identified in (i) for a software development project? [ 4 marks ]. Give 2 marks if the advantages given correspond to the model selected in (i), even if they selected the wrong model! 4

5 (b) In order to test how your system handles stress situations, one approach would be to force it to its limits by supplying a very large amount of input. What is the maximum number of instructors, students, and courses that can be used to test how your system handles stress situations? Explain how you obtained your answers [ 4.5 marks ]. Instructors = 1000: instructor ID Students = 10000: student ID Courses = 3000: an instructor can teach a maximum of 3 courses. Give 1.5 marks for each correct answer; 1 mark for the correct value and 0.5 for the explanation. (c) You have been approached by the University to make the following modifications to the original project. Due to an increase in the number of students enrollment, a course can have multiple sections. In order for a course section to be offered, there must be between 10 to 30 students registered in the section. A course can require other prerequisite courses to be taken first. The system shall limit the number of course sections an instructor can be assigned to teach to 5. In addition, a course section must have an instructor. The system shall limit the number of course sections a student can register in to 5. The system shall limit the number of TAs assigned to a course section to 5. A course section must have at least one TA. Finally, the system should be modelled such that it is possible for a Person to be an instructor, a student, and a TA. That is, a person can be assigned to teach course sections, assist in course sections, and/or register to take courses. Each Person shall have a unique ID of 4 characters long, each of which is an integer (i.e. 0159). 5

6 i. Identify the design patterns that would be appropriate for this problem and give a brief justification for using them in your design [ 8 marks ]. The abstract-occurrence pattern: a course (abstract class) can have multiple sections (occurrence class). The player-role pattern: a person can have multiple roles at the same time; a student, an instructor, and/or a TA. Deduct 2 marks if any of the patterns above is missing. Give a maximum of 6 marks for identifying the patterns (3 marks for each pattern). Give a maximum of 2 marks for providing justifications for using the patterns (1 mark for each pattern). 6

7 ii. Draw a UML class diagram to incorporate the proposed changes. Your diagram should include the attributes personid, firstname, lastname, password, courseid, course- Name, and other important attributes. For example, you may want to have an attribute for the list of courses a student is registered in inside the student class, etc. Your diagram should only include class methods you use on the sequence diagram on the next page [ 12 marks ]. Deduct a maximum of 4 marks for missing attributes and methods (0.5 mark for each mistake). Deduct a maximum of 3 marks for wrongly labelled multiplicity or missing association (0.5 mark for each mistake). Deduct a maximum of 5 marks for missing classes (1 mark for each mistake). PersonRole 0..3 personid firstname lastname password Person Student coursestakinglist coursetaing TA Instructor coursesteachinglist isregistered haspassed addtocoursestlist istaing 1..5 isteaching Registration grade 1..5 CourseSection sectionid registrationlist requestotoregister addtoregistrationlist 1..5 * courseid coursename Course getprerequisite * prerequisite * 7

8 iii. Draw a UML sequence diagram showing a Person registering for a course. Note that, a Person cannot register for a course he/she is currently teaching, already registered in, or assigned to TA [ 7.5 marks ]. Deduct a maximum of 4 marks for missing conditions (0.5 mark for each mistake). Deduct a maximum of 3.5 marks for not including the classes that should have been included, or using classes that aren t part of their UML class diagram (0.5 mark for each mistake). 8

9 5. [ 20 marks ] Consider the Java function below: 1 public void coveragetest ( int x, int y ) 2 { 3 int f l a g ; 4 i f ( x < 0){ f l a g = 1;} 5 else i f ( x % 2 == 0){ f l a g = 0;} 6 else { f l a g = 1;} 7 i f ( y > x ){ 8 f l a g = x/ f l a g ; 9 } 10 else { f l a g = y/ f l a g ; } 11 } (a) Draw a flowchart diagram for this function [ 5 marks ]. 3 4 T 4_1 F 5 T 5_1 F 6 7 F 10 T

10 (b) Give a test suite that will achieve maximum line coverage on this code in the minimum number of test cases [ 3 marks ]. coveragetest(3,4) coveragetest(3,2) Deduct 1 mark for any extra test case. (c) Give test case(s) that, combined with the test case(s) you gave in part (b), make up a test suite that will achieve maximum node coverage on this code, in the minimum number of test cases [ 3 marks ]. coveragetest(2,3) coveragetest(-1,-2) Deduct 1 mark for any extra test case. (d) Give test case(s) that, combined with the test case(s) you gave in part (c), make up a test suite that will achieve maximum edge coverage on this code, in the minimum number of test cases [ 3 marks ]. The above test cases will be able to achieve maximum edge coverage. Deduct 1 mark for any extra test case. (e) Give test case(s) that, combined with the test case(s) you gave in part (d), make up a test suite that will achieve maximum path coverage on this code, in the minimum number of test cases [ 3 marks ]. coveragetest(-1,0) coveragetest(2,1) Deduct 1 mark for any extra test case. (f) What possible program execution error would your path coverage test suite reveal that your line coverage suite may not? [ 3 marks ] A case when flag is set to 0. This should be consistent with their test cases of line coverage. Deduct 3 marks if the test case they provided for line coverage set the value of flag to 0! 10

11 6. [ 20 marks ] Consider the Java method formattime, whose prototype and purpose is given below. / The method t a k e s the c urrent time in 1 2 hours format and d i s p l a y s i t in 2 4 hours format. For example, i f the current time i s 1 1 : 3 5 AM, the method d i s p l a y s 1 1 : 3 5, and i f i t i s 1 1 : 3 5 PM, the method d i s p l a y s hour the minute t h e timeofday AM or PM / public void formattime ( int hour, int minute, S t r i n g timeofday ) ; (a) Identify the set of equivalence classes for the input of the method formattime [ 4 marks ]. hour: [-infinity..0], [1..12], [13..infinity] minute: [-infinity..-1], [0..59], [60..infinity] timeofday: [AM], [PM], [any other string] Deduct 0.5 mark for each mistake (a maximum of 1 mark per parameter). 11

12 (b) Write a java implementation of the method. Your method should first validate the values of its input parameters. For instance, if the value of the parameter minute is 65, the method should display the message: ERROR: Invalid time [ 6 marks ]. 1 public void formattime ( int hour, int minute, S t r i n g timeofday ) 2 { 3 int hrs ; 4 i f ( ( hour < 1 hour > 1 2 ) ( minute < 0 minute > 59) 5 (! timeofday. e q u a l s ( AM ) &&! timeofday. e q u a l s ( PM ) ) ) 6 { 7 System. out. p r i n t l n ( ERROR: I n v a l i d time ) ; 8 return ; 9 } 10 i f ( timeofday. e q u a l s ( PM ) ) 11 hrs = hour + 12; System. out. p r i n t l n ( hrs + : ) ; i f ( minute < 10) 16 System. out. p r i n t l n ( 0 ) ; System. out. p r i n t l n ( minute ) ; 19 } Deduct 1 mark if the method is too complex to understand! Deduct 1 mark if there is a syntax error Deduct 2 marks if the method fails to do what it was supposed to do. 12

13 (c) As a percentage, what is the maximum degree of line coverage that can be achieved for the code in (b)? Give an explanation [ 2 marks ]. 100% (d) Give a test suite that will achieve the maximum line coverage on the code in (b) in the minimum number of test cases [ 3 marks]. formattime(11, 05, AA) formattime(11, 05, AM) formattime(11, 05, PM) Deduct 1 mark for any extra test case. (e) Explain why line coverage is the weakest coverage measure when performing structural testing. Give a test case to support your answer [ 5 marks ]. It gives a false impression since not all the conditions are checked. formattime(11, 99, AM) Deduct 2 mark if they don t give a test case. 13

14 7. [ 35 marks ] The following UML use case diagram shows the relationships between a set of use cases and actors for a simple library system. Search for a book by Tittle Search for a book by Author Borrower Add a new book Search for a book by ID Delete a book Place a book on hold Change a book's information Check Personal information Librarian Update a Borrower's Information Check out a book Check in a Book Clerk Renew a book Add a Borrower Record fine payment Figure 1: UML use case diagram for the library system 14

15 (a) Redraw the diagram using actor generalization [ 5 marks ]. Search for a book by Title Check Personal Information Borrower Search for a book by ID Search for a book by Author Place a book on hold Check out a book Borrower Update a Borrower's Information Check in a Book Add a Borrower Renew a book Add a new book Clerk Record fine payment Change a book's information Delete a book Librarian Search for a book by title Check Personal Information Deduct 1 mark if they included the two use cases in their generalization, allowing the clerk to inherit them! 15

16 (b) Explain how the following design patterns could be used to model the library system. Give a brief justification for using them in your design. i. The abstract-occurrence pattern [ 5 marks ]. A book (abstract class) could have multiple copies (occurrence class). having to duplicate information common for each copy. Deduct 1 mark if they don t give a reason This avoids ii. The player-role pattern [ 5 marks ]. A person (player class) could have multiple roles. For instance, an employee (clerk or librarian) could borrow books. This prevents instances from changing classes. Deduct 1 mark if they don t give a reason iii. The read-only interface pattern [ 5 marks ]. A librarian can make modifications whereas borrowers are read-only. This allows only the privileged classes to be able to modify attributes of objects that are immutable for others. Deduct 1 mark if they don t give a reason 16

17 (c) Draw a UML class diagram for the library system incorporating the design patterns you identified in (b). Your diagram should show important class attributes and methods [ 15 marks ]. Deduct a maximum of 4 marks for missing attributes and methods (0.5 mark for each mistake). Deduct a maximum of 3 marks for wrongly labelled multiplicity or missing association (0.5 mark for each mistake). Deduct a maximum of 5 marks for missing classes (1 mark for each mistake). PersonRole 0..2 personid firstname lastname password Person Borrower Employee borrowedbooks * Clerk Librarian Loan borroweddate duedate returneddate * BookCopy barcodenumber * Book bookid booktitle authorslist publicationdate 17

18 8. [ 5 marks ] Briefly discuss the factors which contributed to the success (or failure) of your group project. If given another opportunity to do the project again, what would you do differently? They should have full marks for this questions However, deduct 1 mark if their explanation is not clear! 18