2.3 UML Class Models

Question 1

What is UML used for?

Answer 1

To represent our software analysis

Question 2

What is a UML Class Digram?

Answer 2

aka static structure diagram

contains representations of:
- classes
- interfaces
- objects
- relationships

Question 3

What is a Class?

Answer 3

A description of a similar set of instances.

Question 4

What type of word makes a good class candidate?

Answer 4

Nouns

Question 4

What are candidates for a Class?

Answer 4

• domain objects
• roles
• events
  -interactions

Question 5

How is a class represented visually in UML?

Answer 5

Denoted by a rectangle with three horizontally partitioned units.

1. Name (required)
2. Attributes
3. Operations

Question 6

What does it mean when a class name is in italics?

Answer 6

It’s an abstract class.

Abstract classes describe the properties of subclasses but NEVER have their own instances.

Question 7

Why might you want to use an abstract class?

Answer 7

If you have related subclasses that have common features you can factor those features up into the abstract class.

Question 8

What are the symbols for visibility?

Answer 8

+ public
- private
# protected
~ package

Question 9

What attributes can you specify?

Answer 9

• name
• type
• (optional) multiplicity and ordering
• (optional) initial value
• (optional) derivation
• properties e.g., {frozen}

Question 10

What operation parameters can you specify?

Answer 10

• name
• type
• default value
• kind (in, out, inout)

Question 11

What operation properties can you specify?

Answer 11

• {query}
• {concurrency}
• {abstract}
• class scope (shown by an underline)

Question 12

What does an Interface require in UML?

Answer 12

Describe what the interface provides and requires.

Question 13

parameterized classes

Answer 13

Parameterized classes correspond to Java generics

Question 14

nested classes

Answer 14

• suitable for inner classes

Question 15

composite objects

Answer 15

• class diagrams within class rectangles

Answer 16

verbs describe relationships

association - people drive vehicles

generalization - a car is a kind of vehicle

dependencies - dependency between cars and pollution laws: if pollution laws change then cars might have to be adapted

Question 17

Aggregation vs Composition?

Answer 17

Say you have two classes: House and Room.

A House has a Room, but if you destroy the House, you also destroy the Room. Therefore, the association is NOT an aggregation but a Composition (open diamond).

In Composition there’s a responsibility for managing the lifetime of the constituent objects.

A particular constituent can only belong to one Composition.

Compositions also have the transitive property e.g., House can have Rooms and Rooms can have Closets. There is no such property for aggregations.

Aggregation = Open Diamond

Composition = Closed Diamond

Question 18

What is a qualifier?

Answer 18

A class attribute that provides access to instances of a particular class.

e.g., like the key in a database table.

Question 19

What is a link?

Answer 19

Just like classes can have instances, associations can have links.

Question 20

generalization

Answer 20

generalization is not inheritance. inheritance is an implementation whereas generalization is a modeling technique.

Question 21

What is overlapping vs disjoint?

Answer 21

Overlapping means a child class can inherit from more than one parent.

Disjoint means a child class can only inherit from one parent.

Question 22

What is complete vs incomplete?

Answer 22

Does the set of child classes cover all of the instances? if so, it’s complete, else incomplete.