Description
Software Modelling and Design
1 System Outline: An Interactive Quiz System
The outline of the system is as described in Coursework 1, i.e., http://edshare.soton.ac.
uk/20332/
For Coursework 2, you will model the system using Event-B according to the following
requirements.
1.1 Users
The system manages a set of registered users. A user can register with the system with a
password. Registered users can log in to the system using their password. Once logged in, the
user user can log out of the system. (Here, we do not model the fact that a user can log in
using multiple devices.)
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REQ 1 The system manages a set of registered users
REQ 2 The system should allow a user to register with a password
REQ 3 The system should only allow a user to log in to the
system using the correct password
REQ 4 A logged-in user can log out of the system
1.2 Quizzes
Only logged in users can create new quizzes. The user who created a quiz becomes the creator
of the quiz. Each quiz contains a sequence of questions. The creator of a quiz, once logged
in, can create new questions and their answers for that quiz, can update the existing questions
of the quiz and their answers, can remove a question from the quiz, and can remove the quiz
itself.
REQ 5 A logged in user can create a new quiz and becomes the
creator of the quiz
REQ 6 Each quiz contains a “sequence” of questions
REQ 7 A logged in creator of a quiz can create new questions
and answers of the quiz
REQ 8 A logged in creator of a quiz can update the existing
questions and their answers of the quiz
REQ 9 A logged in creator of a quiz can remove a question
from the quiz
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REQ 10 A logged in creator of a quiz can remove the quiz
For each question, the number of possible answers (i.e., the options) is between 2 and 4.
Amongst the options, only one of the answers is the correct one for the question.
REQ 11 Each question has between 2 and 4 possible options
REQ 12 Each question has exactly one correct answer, which
must be one of the options of the question
1.3 Running Quizzes
The quiz can be shared to other registered users of the system by the quiz’s creator, who must
be logged in. Once shared the quiz is accessible to the other users.
REQ 13 The logged in creator of a quiz can share the quiz with
other registered users, who then have access to the quiz.
The state machine of a running quiz can be seen in Figure 1. Any logged in user who has
access to a quiz can start the quiz and becomes the quiz’s host. Moreover, a quiz can have
more than one running instance at the same time. Once started, participants can join a running
instance of a quiz. Participants can be logged in users or anonymous users.
REQ 14 A logged in user who has access to a quiz can begin that
quiz and becomes the quiz’s host
REQ 15 A quiz can have multiple running instances at the same time
REQ 16 Participants (logged in users or anonymous users) can
join a running quiz instance
At each step, the host shows the question and the participants answer the question via their
device. When a question is finished (e.g., when the all participants have answered or when the
host terminates the question early), a summary of the question is shown. After showing the
summary of the question, the host can move to the next question of the quiz if any. At any
point, the host can decide to terminate the quiz early. At the end of a quiz, a summary of the
quiz is shown.
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Figure 1: State Machine of a Running Quiz
REQ 17 At each step, the host shows the question and the
participants answer the question
REQ 18 When a question is finished, a summary of the question is shown
REQ 19 After showing the summary of the question, the host
can move to the next question of the quiz (if any)
REQ 20 The host can finish the quiz when there are no more
questions or terminate the quiz early
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REQ 21 At the end of a quiz, the quiz’s summary is shown
2 Tasks (50 marks)
2.1 Task 1 (5 marks)
Identify the main entities from the system requirements and create a class diagram to represent
the important relationships between these entities. You may reuse your class diagram from
Coursework 1.
2.2 Task 2 (45 marks)
Use the system requirements and the class diagram to create an Event-B model of the interactive
quiz system. Make sure to
• Identify appropriate Event-B sets and constants
• Identify appropriate Event-B variables and invariants. The invariants should clearly specify any constraints between state variables. You may lose marks by not having invariants
to represent constraints.
• Identify appropriate Event-B events. Your model should have the events:
– User registers to the system
– User logs in to the system
– User logs out of the system
– User creates a quiz
– User removes a quiz
– User create a questions (including its options, and the correct answer)
– User updates a question
– User removes a question
– User shares a quiz to another user
– User hosts a quiz
– Register user joins a running quiz
– Anonymous user (guest) joins a running quiz
– The quiz’s host starts the quiz
– Participant answers the question
– Finish a question and show the question summary
– The host continues to the next question
– Finish a quiz and show the quiz summary
– The host ends a running quiz
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• Identify constraints on the variables and model these as invariants, e.g., only logged in
user who has access to the quiz may host the quiz.
Hints You should consider using extension refinement to structure your Event-B model.
Remarks
• Up to 10 marks will be awarded for a model developed using the Rodin platform (see the
submission instructions below).
• Up to 5 marks will be awarded for a model using extension refinement.
• This means a paper-based solution without refinement will have a maximum of 35/50
marks.
3 Submission Instructions
Each group should submit a written report (PDF format, one report per group) giving your
answer to each of the tasks above. Clearly indicate your group number, member names and
email IDs on the front page. Make sure your Event-B models are appropriately commented and
are included in the PDF report. You should also include an archive of your project from the
Rodin tool containing your models. Up to 10 marks will be awarded for the model developed
using the Rodin platform. You should use the automated hand-in facilities found on the student
Web pages at: https://handin.ecs.soton.ac.uk/.
The group allocations are on the course Noteswiki page.
If you feel there are any ambiguities in the requirements feel free to make your own interpretation, but make sure any interpretations you make are clearly indicated in the report. You
should work together as a group to accomplish these tasks. It is the responsibility of each group
to make initial contact and arrange their own group meetings. Please inform us of any problems
contacting your group members. You should avoid discussing your solutions with other groups.
NB: Group size is four . It may be necessary to run one or two groups of three depending on
the size of the class, or any students dropping out. In these cases the workload will be reduced
accordingly.
• Group of 3: You are not required to model the events corresponding to
– User logs out of the system
– User removes a quiz
– User updates a question
• Group of 2: You are not required to model the events corresponding to
– User logs out of the system
– User removes a quiz
– User updates a question
– Anonymous user (guest) joins a running quiz
Furthermore, you can omit the details about question summary and quiz summary of a
running quiz.
6 COMP 1216
