EXERCISES WEEK 1
In this week, you exercise basic data modeling techniques: classes, objects, associations, links,
and constraints. You practice with creating simple data models.
You can create your models on paper or with a (cloud-based) editor for class diagrams on your
laptop, like Visual Paradigm. However, object diagrams cannot be created in editors like Visual
Paradigm.
1. INTRODUCING CLASSES AND OBJECTS
Draw a class Student that has as attributes student number, student name, and date of birth.
Draw an object Ron which is from the class Student. Ron has student number 0001 and is born on
01-01-1985.
MODEL SOLUTION
0001 : Student
Student
Nr = 0001
Name = Ron
BirthDate = 01-01-1985
Nr
Name
BirthDate
2. USING CLASSES, OBJECTS, ASSOCIATIONS, AND LINKS
Draw a class diagram that has two classes: Student and Course:
a. Connect the Student class with the Course class using an association.
b. Add three relevant attributes for each of the classes. For example, for the class Student
you may define student number, student name, and date of birth.
c. Add multiplicity constrains on both ends of the association: a student takes one or more
courses; a course is taken by zero or more students.
Draw an object diagram in which Ron (an object from the class Student) takes the BIM course
(an object from the Course class). Provide values for all attributes of the objects.
MODEL SOLUTION
Student
Nr
Name
BirthDate
takes
*
1..*
Course
Nr
Name
Abbreviation
0001 : Student
1BV00 : Course
Nr = 0001
Name = Ron
BirthDate = 01-01-1985
Nr = 1BV00
Name = Business Modeling
Abbreviation = BM
3. PERSON IS EMPLOYEE OF COMPANY
Draw a class diagram described by the fact Person is Employee of Company and the following
statements:
a.
b.
c.
d.
It is possible that some Person is not Employee of any Company.
Each Person is Employee of at most one Company.
Each Company has at least one Person as Employee.
It is possible that the same Company has more than one Person as Employee.
(Draw one class diagram that addresses all these statements)
MODEL SOLUTION
Person
Employee
1..*
Company
0..1
4. STUDENT TAKES EXAM
a. Model in an object diagram the fact that Ron (whose student number is 237784) takes the
1BB50 exam on 6-Oct-2003.
b. Model the more general situation of students taking exams with the help of a class
diagram.
c. Attach sample extensions (populations) to all classes and associations in your model.
d. Which are the unique attributes in this model? Notice that it should not be possible to
have more than one exam per course per day.
e. Is it compatible with your class diagram for a person to take more than one exam? If this
is not the case, change the class diagram in a way, which makes this possible.
MODEL SOLUTION
237784 : Student
1BB50 20031006 : Exam
StudentNo = 237784
Name = Ron
CourseNo = 1BB50
Date = 06-10-2003
takes/is taken by
Student
{unique}
StudentNo
Name
Exam
CourseNo
Date
*
*
237784
237784
268315
268315
237784 Ron
215497 Ton
268315 Els
{unique}
1BB50-20031006
1R620-20031119
1R620-20031119
1BB50-20031117
1BB50 06-Oct-2003
1BB50 17-Nov-2003
1R620 19-Nov-2003
Note 1: The object identifier in the case of the Exam class is a combination of two attributes:
CourseNo and Date. This ensures that there is only one exam for a given course on a given date.
Note 2: The object identifier is given both in the name of the object and also as value in the class
attributes. Although it may seem redundant, it is not. One indicates the attribute to which this
value belongs, and the other one indicates that this is the object identifier.
5. CONFERENCE MANAGEMENT
In the problem domain of conference management, we may use a class Session for
representing the different sessions of a conference, which consist of a number of paper
presentations, and a class Participant for representing the conference participants. The
following class diagram also contains the chairperson association between Session and
Participant:
*
1
ChairPerson
3 joins
Session
Participant
*
*
a. Is it compatible with the class diagram for a participant to be the chairperson of multiple
sessions at a conference? If not, change the class diagram in such a way that makes this
possible.
b. Add attributes and attach sample extensions (populations) to the classes and the
association in this diagram.
c. Change the class diagram in such a way, which makes it possible for some sessions (for
instance, the main sessions) to have a vice-chairperson (note that a class may be
associated in different ways to another class).
d. Suppose participants evaluate sessions. Extend the class diagram in such a way that it
becomes possible for participants to grade sessions in a session evaluation.
e. Further extend the class diagram such that a session evaluation includes a number of
paper evaluations, and it becomes possible to evaluate each paper with a grade.
MODEL SOLUTION
a+b
*
1
Session
3 joins
SessionNo
SessionName
StartTime
Participant
*
ParticipantNo
Name
*
A1 Theory
9:00
A2 Applications 14:00
B1 Case studies 16:00
A1
A2
B1
ChairPerson
003
017
035
017
003
003
Grefen
Reijers
Angelov
c+d+e
*
1
1
ChairPerson
1
3 joins
Session
Participant
*
1
*
*
ViceChairPerson
0..1
{unique}
3 madeFor
madeBy4
SessionEvaluation
-Grade
*
*
1
*
PaperEvaluation
Paper
*
1
*
-Grade
Note: The uniqueness constraint here is used to indicate that each participant can give only one
evaluation per session. This constraint can be modeled also in a different way (to be
demonstrated in the next lecture).
6. COURSE PREREQUISITES
The following class diagram describes some concepts from the problem domain of university
course management. Courses are given by faculty members. Courses have pre-requisites, that is,
certain other courses have to be taken before a specific course can be attended.
prerequisite
isGivenBy
Course
FacultyMember
CourseID
CourseName
0..1
*
*
1
a. Verbalize the recursive association between courses. Using CourseID as the standard
identifier of the Course class, give a sample extension (population) for this class and the
recursive association.
b. Is it compatible with the given class diagram that a course can have more than one prerequisite course? If this is not the case, change the class diagram in such a way that makes
this possible.
c. Is it possible for several courses to have the same course as a prerequisite? If this is not
the case, change the class diagram in such a way that makes it possible.
d. Express a constraint that prevents a course from being its own pre-requisite.
MODEL SOLUTION
a) Each course has zero or one course as prerequisite. Each prerequisite course has one
(successor) course.
CourseID
IIS10
IBB30
IIS40
IBB80
CourseName
IS Basic
DOM
IS Advance
OO Programming
Pre-requisite
IIS10
IBB30
CourseID
IIS40
IBB80
b) No, it is not possible, because of the "1" multiplicity in the "0..1" constraint.
c) and d)
prerequisite
*
isGivenBy
Course
CourseID
CourseName
FacultyMember
*
*
1..*
{A course must not be its own prerequisite.}
7. R&D PROJECT FUNDING
Governmental agencies use certain rules for funding research and development (R&D) projects.
The following remarks describe an information system that helps to put together committees for
evaluating R&D project proposals.
In general, a new R&D funding program is started by issuing a call for proposals (CFP) that
specifies a number of themes for which project proposals can be submitted. When the submission
deadline has passed, the project proposals submitted for a specific theme are evaluated by a
committee composed of external experts that are competent for this theme. One of the committee
members is appointed as chairperson. A theme may appear in more than one CFP. A CFP has a
unique reference number, a research program name, a date of publication, and an available
budget. The following information about experts is kept up-to-date: a unique identification
number, name, gender, date of birth, and the themes for which the expert is competent.
Make a class diagram including the most important object classes and constraints.
MODEL SOLUTION
1..*
1
isEvaluatedBy
0..1
ProjectProposal
Committee
*
*
*
*
refersTo
isSubmittedInResponseTo
{unique}
3 isMemberOf
1
2..*
1
CFP
RefNo
ProgramName
DateOfPublication
Budget
SubmissionDeadline
1
{unique}
Expert
Theme
*
1..*
*
*
ExpertID
Name
Gender
DateOfBirth
1
Chairperson
{Chairperson of committee must be member of committee }
Optional: for isMemberOf association, use role name Member at end of Expert
8. EXEMPTIONS AT THE OPEN UNIVERSITY
Students at the Open University (OU) have often completed other studies before they start
studying at the OU. They are usually eligible for exemption from part of their study programme
at the OU, as a result of their previous studies. A simplified description of the process involved in
such an exemption request is given below for someone hoping to study information science. An
information system for handling the exemption requests and decisions is to be developed. For
each student, a student number, name and address are registered. Many students have completed
one previous course of study; for example, Information Science at a higher technical college
(HTS), Dutch law or Tourism studies. There are now two possibilities:
Possibility 1
For several common types of previous study (such as Information Science at HTS), there are
standard exemption profiles (one for each previous study). Such a profile shows whether or not
there will be an exemption, for each subject to be followed at the OU. If the student has
completed one of these previous studies, the exemption decision for a subject will be justified by
means of the profile that applies to the student.
Possibility 2
If the student’s previous study does not fit into any standard profile, then the student must hand in
a request for which subjects he or she would like to be exempted. The decision, whether or not an
exemption is granted, is then registered per subject. If no exemption is granted for a particular
subject, then the reason for that is also registered.
Make a class diagram. State any assumptions that you have made.
MODEL SOLUTION
Student
StudNo
Name
Address
*
0..1
3 isFor
hasCompleted
Study
ExemptionProfile
1
*
0..1
*
exempts
1
isReasonFor
1..*
makes
refersTo
ExemptionRequest
*
1
Subject
*
1..*
1
*
1
consistOf
ExemptionDecision
1
1..*
ExemptionDecisionBySubject
Decision
Reason
*