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1 Student name: Student number: Examination cover sheet (to be completed by the examiner) Course name: Software specification and architecture Course code: 2IW81 Date: Start time: 09:00 End time : 12:00 Number of pages: 11 Number of questions: 5 Maximum number of points/distribution of points over questions:100 Method of determining final grade: divide total of points by 10 Answering style: multiple choice questions; open questions Exam inspection: With your instructor Other remarks: It is not allowed to use study materials or a computer during the exam. The examination questions have been inspected by Julien Schmaltz, Kees Huizing, Anton Wijs, Loek Cleophas, and Serguei Roubstov. Instructions for students and invigilators Permitted examination aids (to be supplied by students): Notebook Calculator Graphic calculator Lecture notes/book One A4 sheet of annotations Dictionar(y)(ies). If yes, please specify: Other: Important: examinees are only permitted to visit the toilets under supervision it is not permitted to leave the examination room within 15 minutes of the start and within the final 15 minutes of the examination, unless stated otherwise examination scripts (fully completed examination paper, stating name, student number, etc.) must always be handed in the house rules must be observed during the examination the instructions of examiners and invigilators must be followed no pencil cases are permitted on desks examinees are not permitted to share examination aids or lend them to each other During written examinations, the following actions will in any case be deemed to constitute fraud or attempted fraud: using another person s proof of identity/campus card (student identity card) having a mobile telephone or any other type of media-carrying device on your desk or in your clothes using, or attempting to use, unauthorized resources and aids, such as the internet, a mobile telephone, etc. using a clicker that does not belong to you having any paper at hand other than that provided by TU/e, unless stated otherwise visiting the toilet (or going outside) without permission or supervision Associated with the Central Examination Regulations

2 TECHNISCHE UNIVERSITEIT EINDHOVEN Department of Mathematics and Computer Science Examination Software specification and architecture Tuesday, April 12th 2016, 09h00 12h00. Your answers must be formulated and written down clearly. First read ALL questions once! This examination consists in two parts: the first part is composed of 20 multiplechoice questions. Each question gives you 2 or 0 points. The second part is composed of 4 exercises worth 20 points each. You need to complete at least 3 of these exercises. Students following 2IHS10 need to address questions 1 to 12 and the first two exercises (exercise A and exercise B). Multiple Choice Questions (40 points) Answer the following multiple-choice questions. Each question has only one correct answer. You should encircle your answer. For each question, you will get 2 points if you circled the correct answer; 0 point otherwise. Question 1 Consider the statement "The system shall be able to process up to 40 executing jobs at a time". Among the four options below, select the best formulation for this statement as a requirement: a. The system shall not be able to process more than 40 jobs at a time. b. The system shall process jobs up to 40 simultaneous jobs. c. The system shall be able to process jobs up to 40 simultaneous jobs. d. The system shall process typically 40 jobs at a time. Question 2 Select from the requirements below, the one that is S.M.A.R.T. a. The system shall start quickly. b. The system shall start in a few seconds. c. The system shall start within 4 seconds. d. The system shall start as fast as possible. 1

3 Question 3 Select the answer below that best describes the relation between the three use-cases A, B, and C below: a. Use-case A always executes use-case B and always executes use-case C. Question 4 b. Use-case A always executes use-case B and sometimes executes use-case C. c. Use-case A sometimes executes use-case B and always se-case executes C. d. Use-case A sometimes executes use-case B and sometimes executes use-case C. Which of the following statements pertaining to actors in use-cases is "FALSE"? a. In presence of generalization a more general actor can always replace the specialized one. b. One user might be represented by multiple actors in the same use-case. c. Actor is a class of entities falling beyond the system boundaries and interacting with the systems. d. One use-case might involve multiple actors. Question 5 Consider the class diagram below composed of 3 classes, namely, A, B, and C. Which of the following statements about this class diagram is "TRUE": a. When an instance of A is deleted, all instances of B are deleted. Instances of C are unchanged. b. When an instance of A is deleted, all instances of B created by A are deleted. Instances of C are unchanged. c. When an instance of A is deleted, all instances of B created by A are deleted. Instances of C are deleted as well. d. When an instance of A is deleted, instances of B and C are unchanged. 2

4 Question 6 Consider the class diagram below composed of 3 classes, namely, company, role, and contract. Note that no multiplicity means a multiplicity of 1. Which of the following statements about this class diagram is "TRUE": a. Every company can have only one contract. Question 7 b. Every company can play only one role per contract. c. Every contract can be associated to only one company. d. Every company can have multiple roles within one contract. Consider the class diagram below composed of 2 classes, namely, A and B. Which of the following statements about this class diagram is "TRUE": a. A is a generalization of B. b. A is a composition of B. c. B is an implementation of A. d. B is a generalization of A. Question 8 Consider the class diagram below composed of 2 classes, namely, plane and flight. Which of the following statements about this class diagram is "TRUE": a. One flight can be assigned only to zero or one planes. b. One flight can be assigned to any number of planes. c. One plane can be assigned only to zero or one flight. d. One plane must be assigned to at least one flight. Question 9 Consider the sequence diagram below composed of 2 instances of classes A and B. Which of the following statements about this class diagram is "TRUE": 3

5 a. Method1 must be implemented by class B. b. Method1 must be implemented by class A and B. c. Method1 must not be implemented by A nor by B. d. Method1 must be implemented by class A. Question 10 Consider the sequence diagram below composed of 3 class instances, namely, A, B, and C. Which of the following statements is not enforced by the sequence diagram: a. m1 is received before m2 is sent. b. m2 is received before m3 is sent. c. m1 is sent before m2 is sent. d. m2 is sent before m3 is sent. Question 11 In the activity diagram below, which one of the executions (to completion) is not possible? a. A completes then C completes. B starts but is killed. b. B completes then C completes. A starts but is killed. c. A and B complete, C completes once. d. A and B complete, then C completes twice. Question 12 Consider the UML state machine below. Consider the sequence of events: e1, e3, e4, e5, e2. What state is reached at the end of this sequence? 4

6 H 1 e1 e2 2 a. 1 b. 2 c. 3 e3 e5 d. 4 3 e4 4 Question 13 Consider a traffic light. Whenever the light becomes green, it remains green until it becomes orange. It might remains orange for some time before it eventually becomes red. Which of the following LTL formulas expresses this statement? a. G(green green U (orange U red) b. G(green U orange U red) c. G(green X(green U (orange U red)) d. G(green X(green U (orange (orange U red))) Question 14 Consider a printer. A user can access the printer by sending a req signal to the printer. The printer will grant access to its services by responding with an ack signal. A requirement of the printer is to be fair, that is, it eventually serves all requests. Which of the following LTL formulas expresses this statement? a. G(req U ack) b. G(req Fack) c. G(req ack) d. GF(req ack) 5

7 Question 15 Consider the Labelled Transition System (LTS) below over atomic propositions a and b. Which of the following LTL properties holds for this LTS? a. GFb b. FGb c. Ga d. Gb Question 16 Which statement about the notion of "Time convergent sequences" of Timed Automata is "TRUE"? a. Time convergent sequences are flaws in model. b. Time convergent sequences come from zeno paths. c. Time convergent sequences cannot be avoided. d. Time convergent sequences are only present in models with timelocks. Question 17 Which statement defines the notion of "Timelock" in the theory of Timed Automata? a. A Timed Automaton has a timelock in state s if and only if there are no zeno paths starting from state s. b. A Timed Automaton has a timelock in state s if and only if there are no infinite sequences starting from state s. c. A Timed Automaton has a timelock in state s if and only if there are no time divergent sequences starting from s. d. A Timed Automaton has a timelock in state s if and only if there are no time convergent sequences starting from s 6

8 Question 18 Consider the Timed Automaton below over atomic propositions start and stop and clock x. The initial state is state number 0. Select the statement below that holds for this Timed Automaton a. This timed automaton has a timelock. b. This timed automaton has a zeno path. c. The time spent in state 1 is at least 2 time units and at most 5 time units. d. When in state 1, a stoptransition always takes place when clock x equals 2. Question 19 Which stakeholders are addressed by the process view of the 4+1 Views model of Kruchten: a. end-users b. programmers c. system integrators d. system engineers Question 20 The Gnutella protocol is an open decentralized group membership and search protocol. Gnutella has been designed to operate in a dynamic environment, where hosts can join and leave the network frequently. Furthermore, Gnutella is expected to be scalable and reliable, that is, external attacks should not cause significant data or performance loss. Which one of the following architectural styles would you apply if you would be designing Gnutella? a. Blackboard b. Client-server c. Peer-to-peer d. Mobile code 7

9 Exercises (60 points) The second part of the examination consists in four exercises, 20 points each. You should answer at least three of these exercises. Please read all exercises first, choose the ones you are most comfortable with. Should you decide to answer four exercises, we will consider the three best solutions. Please, keep in mind that three correct solutions will give you more points than four wrong ones! Exercise A (Class Diagram) An internet shop sells items via shopping carts. Customers have a name, delivery address, address, and preferred payment strategy (see below). A customer has at most one shopping cart to which he/she can add and remove items. When finished with shopping, the customer takes the cart to checkout. There are several payment strategies (credit card, Paypal, ideal) that can be chosen (or changed) at checkout. After successful checkout, an order is created that is kept in a list of standing orders, until the order is delivered. Write a class diagram that models the internet shop described above. Pay attention to multiplicities. Do not add attributes for references that are drawn as relations (arrows representing association, etc.). Do not add getter and setter methods for attributes. Exercise B (General UML diagrams) Consider a software system supporting the work process of the TU/e Bureau for Computer Facilities (BCF). This bureau handles purchase laptop requests from employees. A case worker within BCF receives that request and monitors it until it is ordered and received. Case workers process the requests for laptops under Euro s, write a purchase order, and then send it to the approved vendor. Purchase requests over Euro s must first be sent out for a bid from the vendor that supplies the product. When the bids return, the case worker selects one bid. Then, the case worker writes a purchase order to be sent to the approved vendor. Once a laptop is received, BCF workers need to register it for easy network access and administrative purposes (who has which laptop). BCF also creates a special BCF account on every laptop for remote maintenance. It might happen that a laptop is given to its user before it is properly registered (say, the MAC address has not been registered). In that case, the software system will automatically send reminders to BCF workers to complete the laptop registration. a. (6 points) Draw a use case diagram for the BCF software system. In addition, give a detailed scenario (pre-condition, trigger, post-condition, main scenario, alternatives) of one of the use cases of your use case diagram. 8

10 b. (6 points) Based on the description of your scenario, draw an activity diagram for it. c. (6 points) Based on the description of this scenario, draw a sequence diagram for it. d. (2 points) informally argue about the consistency between the different diagrams. 9

11 Figure 1: Paper producer machine. Exercise C (LTL and TA) Consider the system shown in Figure 1. It is composed of a Machine, a coffee craving Person, and an Observer. The Machine is a coffee machine accepting coins as input and producing coffee. As you can see from the Timed Automaton of the Person, the Person repeatedly (tries to) insert a coin, (tries to) extract coffee after which (s)he will make a publication. Between each action the person requires a suitable time-delay before being ready to participate in the next one. The machine takes some time for brewing the coffee and will time-out if coffee has not been taken before a certain upper time limit. As a requirement we want the overall behaviour to ensure that the indicated Observer experiences a constant flow of publications from the system. In particular we want the Observer to complain if at any time more than 8 time-units elapse between two consecutive publications. a. (8 points) Create a Timed Automaton modelling the Machine and a Timed Automaton modelling the Observer. The objective is to insert state labels to all these models so that it is possible to express the following properties. You must also formalise those properties in LTL: (a) The Observer never complains. (b) If a coin has been inserted and next coffee has been received, a publication will eventually follow. (c) If a coin has been inserted, coffee is eventually produced. 10

12 b. (2 points) Do the models have timelock or zeno paths? Motivate your answer. c. (10 points) In the previous you formalised three properties. Do they hold? If yes, justify your answer. If not, please provide a counter-example to each property. A counter-example is a finite trace so that at the end of the trace the property is violated. If the properties do not hold, correct your models. Explain the motivation for your changes. 11

13 Exercise D (Architecture) (David Parnas, 1972) The KWIC ("keyword in context") index system accepts an ordered set of lines, each line is an ordered set of words, and each word is an ordered set of characters. Any line may be "circularly shifted" by repeatedly removing the first word and appending it at the end of the line. The KWIC index system outputs a listing of all circular shifts of all lines in alphabetical order. For example, given the following lines as the input: Programming methods Software specification and architecture Software engineering KWIC can be expected to produce the following output: and architecture Software specification architecture Software specification and engineering Software methods Programming Programming methods Software engineering Software specification and architecture specification and architecture Software While full-text search is possible these days instead, a KWIC index system may still be used in e.g. a search engine to show the context of a queried keyword in a search results. Your goal is to define a software architecture for the KWIC system. a. (5 points) Decide on the functional blocks needed for this system. b. (5 points) Select an architecture style to map these functional blocks to an architecture. Why and how would you use this style? c. What are the advantages and the disadvantages of your architecture? Consider how your architecture accommodates (a) (2 points) changes in data representation (e.g., circular shifts are stored as separate entities or lines are stored only as they have been entered and shifts are indicated using an index), (b) (2 points) changes in the algorithm (e.g., lines can be shifted as they are read or after all lines have been read and sorting can be done incrementally), 12

14 (c) (2 points) new functionality being added (e.g., removal of so-called stop words such as "and" or "the", or adding/removing case-sensitivity), (d) (2 points) huge amounts of data to process, (e) (2 points) the need to reuse some of the KWIC components as building blocks for a different system? 13