1. Class Diagram
M. Seidl, et al., Introduction to Object-Oriented Modeling, Springer, Chaper 4. Soft copy (pdf) downloadable freely through UTEP library.

2. Class Diagram Models data, entities and static structures
Most important and most widely-used diagram in UML
Central model due to stability (of data), say, compared to functionalities such as use cases.
Describes the structure of a system by showing the system's classes, their attributes/operations, and the relationships among the classes

3. Example: PC Architecture
0..2
0..2
interface
IdeDevice
Motherboard
IdeBus
interface ScsiDevice
CdRom
{abstract}
HpCdWriter
LaserController

4. Types of Relationships
Construct
Notation
Association
Aggregation
Composition
Generalization
Realization
Dependency

5. Association General binary relationships between classes
Commonly represented as direct or indirect references between classes
Student
Course

6. Association Details Can express the following optional information
Association name (e.g., enroll)
Navigability (e.g., ->)
Multiplicity (e.g., 10..*)
Role names (e.g., course) 1 2
enroll
Student
Course
10..*
course 3 4

7. Association Name
May have an optional label consisting of a name and a direction drawn as a solid arrowhead with no tail.
The direction arrow indicates the direction of association with respect to the name, i.e., the direction in which the name should be read.
Use a verb or verb phrase.
advise
Faculty
Student

8. Navigability
An arrow may be attached to the end of path to indicate that navigation is supported in that direction.
advise
Faculty X
Student

9. Multiplicity
Optional multiplicity specification defining the number of objects that can participate in an instantiated relation
On one or both association ends
The multiplicity specifies an integer interval, e.g.,
l..u closed (inclusive) range of integers
i singleton range
0..* entire nonnegative integer, i.e., 0, 1, 2, …
advise 1
0..*
Faculty
Student

10. Role Names Optional role name on one or both association ends
Use a noun or noun phrase describing the semantics of the role.
advise 1
0..*
Faculty
Student
advisor
advisees

11. Exercise Write skeletal Java code conforming to the following model.
10..*
enroll
0..*
Student
Course
1..3
0..*
taught
instructor 1
advised 1
Faculty
advisor

12. Aggregation
Special form of association representing has-a or part-whole relationship.
Distinguishes the whole (aggregate class) from its parts (component class).
No relationship in the lifetime of the aggregate and the components (can exist separately).
Aggregate
Component

13. Composition Stronger form of aggregation
Implies exclusive ownership of the component class by the aggregate class
The lifetime of the components is entirely included in the lifetime of the aggregate (a component can not exist without its aggregate).
Composition
Component

14. Example University 1..* 1..* 0..* College Department Student chair-of
member-of 1
1..*
Faculty

15. Generalization And Realization
An extension relation is called specialization and generalization.
An implementation relation is called realization.
Superclass
Superinterface
Interface
Subclass
Subinterface
Class
extension of
classes
extension of
interfaces
implementation
of interfaces

16. Example Student {abstract} Graduate {abstract} Nondegree Undergraduate
Master
PhD

17. Dependency
Relationship between the entities such that the proper operation of one entity depends on the presence of the other entity, and changes in one entity would affect the other entity.
The common form of dependency is the use relation among classes.
<<use>>
Class1
Class2

18. Exercise: Strength (Coupling)?
Association, aggregation, composition, generalization, realization, and dependency.
Weakest
Strongest

19. Class Details
The UML notation for classes is a rectangular box with as many as three compartments.
Name
attribute1 ……
attributen
operation1 …
operationn
The top compartment show the class name.
The middle compartment contains the
declarations of the attributes (fields) of the class.
The bottom compartment contains the
declarations of the operations (methods) of the class.

20. Example Attribute type Name of the class Attribute name
Student
- name: String = “John” {readOnly}
- courses: Course [*]
+ register (c: Course)
+ isRegistered (c: Course) : Boolean
Other Properties
Visibility:
+, -, #, ~
Default value
Multiplicity
Operation
name
Return value
Parameters 20 20

21. Inline vs. Diagram Notation
Two ways to express associations
Use either one, but not both. 1
Course
Instructor
Course
-instructor: Instructor
-students: Student[10..*]
-instructor
10..*
-students
Student

22. Guidelines Identify important data, entities, and domain concepts
List all nouns or noun phrases
Determine candidate classes
Define relationships among classes
Association/aggregation: has-knowledge-of, is-part- of
Generalization/realization: is-a relation
Define responsibilities of classes (operations)
Define internal structures of classes (attributes)
Refine, refine, refine …

23. Exercise
Form a pair.
Model the Battleship game by drawing a class diagram; focus on the functional core (or business logic), not UI.
Assume:
A board consists of n*n places (or squares), where n >= 10.
A player’s feet consists of 5 ships: aircraft carrier (size 5), battleship (4), frigate (3), submarine (3), and minesweeper (2).
Ships can’t overlap when placed on a board.

24. Sample Solution has_fleet_of Ship isSunk 5 0..1 is_placed_on
s: ship size
0, s
Game
activePlayer
changeTurn
isWonBy
Place
hit
isHit
place_ships 2 1
n*n
Player
Board 1
pick_place_of
ComputerPlayer
placeShips 1
Strategy
pickPlace

25. Exercise
Any ambiguity or impreciseness in the previous class diagram? Find and list all of them.
How to know that the previous diagram is a “correct” or “good” design/model?
Refine it by introducing more public operations from the client view point.