CSC302 Engineering Large Software Systems page 1/8 Faculty of Arts and Science University of Toronto Midterm Test Department: Computer Science Instructor: Steve Easterbrook Date and Time: 10:10am, Thursday 26th Feb, 2009 Conditions: Closed Book Duration: 50 minutes This test counts for 20% of your final grade Name: _______________________________________________________ (Please underline last name) Student Number: _______________________________________________ Question Marks 1 ______________/20 2 ______________/20 3 ______________/20 Total___________/60 = _________%CSC302 Engineering Large Software Systems page 2/8 1. [Short Questions; 20 marks total] (a) [Software Architectures – 5 marks] What are coupling and cohesion, and why are they important in software design? Suggest measurable properties of a software design that can be used as indicators of the amount of coupling and cohesion. Coupling – a measure of the degree of interaction between software modules, e.g. the amount of knowledge each module needs to have about the other modules. Can be measured by looking at the number of method calls between modules, the number of parameters passed, etc. Cohesion – a measure of how well the things grouped together in a module belong together logically. Could be measured by looking at the number of internal method calls within a module, etc. These are important because they affect maintainability – if coupling is low and cohesion is high, it should be easier to change one module without affecting others. (b) [Scaling Agile methods – 5 marks] Describe two aspects of agile software development that don’t work well on very large software projects, and identify alternative strategies that can be used in their place. At what size of project do you expect such problems to kick in? [Many possible answers. Must have two distinct aspects, and cover alternative strategies and project size considerations for each. Suggestions include:] (1) Emphasis on face-to-face communication over documentation. This starts to breakdown when you have more many team members than can comfortably meet regularly as a team. E.g. meetings of more than around 10 people are unproductive, because it is hard for them all to contribute to the discussions. For larger teams, some of the communication must be in written form, e.g. through use of wikis, email, bulletin board systems, etc, to ensure the larger team communicates effectively. (2) Self organizing teams – developers decide for themselves which tasks to work on. This starts to break down when there are so many team members that you can no longer remember who’s working on what. Again, that’s probably around 10-12 people, although the size depends on how well the team members know one another. Alternative strategies include breaking the team up into subteams, and getting each subteam to work on a different module, or using a workbreakdown structure to identify tasks and allocate people to work on them.CSC302 Engineering Large Software Systems page 3/8 (c) [Uses of UML – 5 marks] What would you use a UML Sequence Diagram for? What are its advantages when used for this purpose? A UML Sequence diagram shows one possible way in which a set of objects can collaborate by message passing to carry out some task. It can be used as a detailed elaboration of a use case during the design process, to decide how the use case will be implemented, and to check that the implementation is feasible. The advantages of this use is that it bridges between the high level description of a use case that would be appropriate for the user to see, and the design of the program in terms of classes and methods. The sequence diagram demonstrates that a specific sequence of method calls between objects can implement the behaviour described in the use case. [note: other possible answers: use for debugging a complex program behaviour; use to compare two different designs to see how much coupling there is; use for documenting the expected behaviour of a design pattern, etc. (d) [Software Estimation – 5 marks] What is 3-point estimation? Why would you use it? Three point estimation involves asking a programmer to provide three different estimates of the amount of time it will take to perform a specific task: the expected time (e), the worst case (w) and the best case (b). These three estimates are then combined by calculating (w+4e+b)/6. 3-point estimation has been shown to provide more accurate estimates than asking for a single number, because it forces the programmer to think more carefully about the upper and lower bounds, and hence to be more realistic. As this type of estimation works best on small tasks, it could be used when planning an upcoming release on an agile development project, for calculating the estimated time needed to build each function requested by the user.CSC302 Engineering Large Software Systems page 4/8 2. [Domain Models – 20 marks] The following domain model captures some basic information about a kids’ karate club. In answering the following questions, state any assumptions that you make. a) How many times can a student attempt to earn a Black belt? [2 marks] As many times as they like (including none). This is because the student can make 0..* belt attempts, each of which is associated with exactly one grading, and each grading is associated with exactly one belt colour. b) The model distinguishes between ‘student’ and ‘person’. Why do some associations go to ‘Student’, and some to ‘Person’? Are these modeling decisions sensible? [2 marks] The distinction allows for people other than the students themselves (e.g. parents) to make payments for their membership. The distinction is useful because it allows us to say there are somethings only students can do (e.g. belt attempts) and some than anyone can do (e.g. pay). c) What are the implications of the multiplicities on the association between Person and Payment? [2 marks] Each person can make many payments, and each payment belongs to exactly one person. The 1..* implies that the only people we are interested in are those that have made at least one payment. The ‘1’ implies that it is not possible for several people to split a bill. d) Does it matter that ‘Person’ is not associated with ‘Family’? [2 marks] The model only allows us to record family relationships between students (e.g. siblings who are all
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