CS 213 Assignment 4 UML for Online Discussion Forums solution




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In this assignment you and your partner will develop an object-oriented design and draw the UML, for the
discussion forums hosted on a website.
Read the DCS Academic Integrity Policy for Programmming Assignments – you are responsible for this. In
particular, note that “All Violations of the Academic Integrity Policy will be reported by the instructor to the
appropriate Dean”.
NOTE: If you feel the impulse to ask a question about the assignment on the Forum, firstmake sure you
have read this description carefully, and then read FAQs. Chances are your question is already answered
Online Discussion Forums
There is a website that hosts discussion forums. A person first needs to be a registered user on the website
before they can participate in one or more forums. A user does not necessarily have to be a member of any
The website hosts several forums.
Each forum has one or more members.
Members of a forum can:
1. post messages to the forum
2. read messages posted by other members to the forum, filtered and/or sorted by message
author, thread, or date
filtered by author means to extract all messags posted by a specific author
filtered by thread means to extract all messags posted in a specific thread – the basis of
filtering is the subject of the initiating message for that thread
filtered by date means to extract all messages posted on a specific date, or within a
range of dates
sorting by author (alphabetically arranging by name) can be done on all messages in the
forum, or on messages in the by-date or by-thread filtered subsets above
sorting by date (chronological/reverse chronological sequencing) can be done on all
messages in the forum, or on messages in any of the filtered subsets above
sorting by thread doesn’t really apply – technically it’s possible to sort all messages in the
forum by initiating message subject, but I can’t see how that would be useful
3. leave a forum
Each message is part of a discussion thread. It can be the initiating message for a new thread, or a
response to a previous message in a thread
Users on the website can:
1. create new forums
2. join an existing forum as member
Every forum has a single owner, who is initially the creator of the forum. The creator of a forum
automatically becomes its first member.
11/5/21, 2:43 PM CS 213 Fall 2021: Assignment 4
https://www.cs.rutgers.edu/courses/213/classes/fall_2021_venugopal/uml/uml.html 2/3
Each forum has one moderator, who is initially the creator of the forum. Only a forum member can be
its moderator.
Owners can:
1. invite users to join their forum by sending them an email invitation
2. invite a member to be the moderator – if the invitation is accepted, the new moderator replaces
the current moderator
3. invite a member to take over ownership – if the invitation is accepted, the ownership is
transferred to that member
4. delete the forum
Moderators can:
1. deny or pass through messages posted to the forum by members
2. resign as moderator by sending an email to the owner, at which point the owner becomes the
Choose the most appropriate representation for each entity in the model. (Entity here refers to class or
interface.) Use interfaces and abstract classes as needed. In each class, list the key attributes and methods
you determine are needed to fulfill the specification. Not all details are explicitly mentioned in the
specification above, but must be filled in by inference. Such details include choice of attributes and their
data types, choice of operations with parameters and return values, and choice of access levels
(public/protected/package/private) for attributes and operations.
Pay special attention to the relationships between entities. Remember, super-sub classes, and interface
implementations are the strongest connections between entities, followed by associations, followed by
dependencies. Make sure you are as specific as you can be with the multiplicities in associations, and
whether an association is a plain old link or an aggregation or a composition, whether it is bidirectional,
unidirectional or reflexive. Note: Every association is by definition bidirectional unless you explicitly show
unidirectionality. Make sure you show multiplicities for all associations.
Supplement to the UML
For each association, list the data structure(s) (full type definition in Java) that will be used to implement the
data that arises out of the association, and name the class(es) to which it/they will belong. (Refer to Slide 7–
Relationship data–of the lecture notes in Week 8->uml-2.pdf for an example. This is also emphasized in the
UML Class Diagram – Part 2 video of Week 8 Lessons.) You are not required to write the class outline. Just
draw a table with two columns, one for each data structure type definition, and the other for the class in
which it will be defined. If the class is not either of the end points of the association, but a new class
altogether, then make this fact explicit in the table.
Your UML and supplement will be graded on completeness, appropriate choices in class/interface/abstract
class for entities, in relationships between entities, and in the data structures used to implement associationspecific data. “Appropriateness” speaks to the best applicable/most precise design choices based on all the
object-oriented design issues we have covered in class, flexibility (how easy it is to use your design for a
range of functionality), extensibility (how easily your design can be extended to add more capabilities),
maintainability (how easy it is to fix problems that may be arise in implementation). Not all of these may
apply with equal importance (every model is different) but you want to use this as a checklist against your
design to spot, and correct, obvious flaws.
Submission Instructions
Submit a single PDF file, called forums_uml.pdf, to Canvas. (Whatever software you use to draw the
diagrams/write text, you MUST convert to PDF.) The PDF document should have the UML as well as the
supplementary table of data structures. If you have trouble fitting the UML in one page, draw the UML with
only the class names and relationships between them on one page, and then on other pages, draw the
details for each entity. Hand-drawn/hand-written submissions will NOT be accepted.
11/5/21, 2:43 PM CS 213 Fall 2021: Assignment 4
https://www.cs.rutgers.edu/courses/213/classes/fall_2021_venugopal/uml/uml.html 3/3
Submit ONE PDF for your team, but write the names of both partners in the document.
Frequently Asked Questions
Q: Do we need to show functionality for a User to register to the website?
A: No.
Q: Can we assume that a user can only be a user of this particular forum’s website, or can these users be a part of
other websites?
A: Yes, you can assume that a user can only be a user for this particular forum’s website.
Q: What’s the difference between the supplementary table of relationships and the UML Class diagram? For
example, would an ArrayList implemented in a class go in the diagram as well as the table of relationships?
A: As can be seen on “Slide 7–Relationship data–of the lecture notes in Week 8->uml-2.pdf”, ArrayList is not
attribute in the class diagram, so it belongs to the table
Q: Does a UML diagram include constructors?
A: No.
Q: Do we need to include the following in our diagram?
“if the invitation is accepted, the new moderator replaces the current moderator”
“if the invitation is accepted, the ownership is transferred to that member”
Or is it just enough to show that the owner can send these invitations?
A: The invitation association is good enough.
Q: Does “deny or pass” imply that a message cannot be shown on the forum until reviewed by a moderator?
A: Yes.
Q: Can a user account be deleted? Can a message be deleted later on?
A: You don’t need to consider these scenarios for the assignment.