1. Structural Modeling

2. Objectives
Define the purpose of structural models

3. Structural Models: Introduction
Use-case and activities describe how a system behaves
Structural models describe a static view of
The data stored in a system
The interface describing how that data is accessed
Structural models ultimately become class diagrams
This data and interface together form a class
We are back to OOP

4. Classes and their Members
A class is a template or blueprint for an object
It’s attributes store data
It’s operations (method) act on the data
Triggers are a special form of method
Responsibilities

5. Class Relationships Some classes have relationships to each other
They fall into 3 categories
Generalization
Aggregation
Association

6. Generalization We again talk about an “IS-A” relationship
Your book calls it a “a kind of” relationship
We inherit attributes and methods from other classes
The inherited class is called the base class or super class
The inheriting class is called the derived class or subclass

7. Aggregation Aggregation relates to “the parts of a whole”
X is a part of Y
A transmission is part of a car
An engine is part of a car
The inverse of aggregation is decomposition
An engine can be part of other things than a car

8. Association You saw association related to use-case diagrams
Associations between classes are more loosely defined than generalization and aggregation
A professor writes a book

9. The Process of Identifying Objects
So how do we figure out how to structure classes, their attributes and their methods?
What are the relationships between classes?
There are a few common techniques to do this
Textual analysis
Brainstorming
Use-case narratives and diagrams
CRC cards

10. Identifying Objects: Textual Analysis
Review use-case diagrams and text in use-case descriptions based on the following rules
Common nouns imply a class objects
Adjectives imply attributes
A doing verb implies an operation (method)
A transitive verb implies an operation
A doable activity with a direct object
A having verb implies an aggregation or association relationship

11. Identifying Objects: Other
Brainstorming is designed to think up new and non-obvious ideas
Common object lists
Lists of objects belonging to a particular category

12. CRC Cards Class-Responsibility-Collaboration diagram
They provide a rough cut analysis of a class interface

13. CRC Card: Example

14. CRC Card: Parts Header Class name Description
Type (concrete or abstract)
Associated use-cases (optional)

15. CRC Card: Parts
A two-column layout of responsibilities and collaborators
Responsibilities
Collaborators
CreatePurchaseOrder
Vendor / Material
EditPurchaseOrder
CancelOrder
Vendor
ApprovePurchaseOrder
ReceiveGoods
Material
PayVendor
Vendor / AccountsPayable

16. CRC Card: Parts Lists of attributes and relationships Attributes
PurchaseOrderID
PurchaseOrderAmount
Vendor
Relationships
Type
Generalization
Order
Aggregation
OrderItem ShippingInstructions

17. Class Diagrams
From the CRC cards, we can create more formal class diagrams
They depict
Classes having attributes and methods
Relationships between classes
Cardinality

18. Class Diagrams: Members
A class diagram lists the class name, attributes and operations in sections
Attributes appear as name: type
Methods appear as name(parameter list)

19. Class Diagrams: Inheritance
Drawn a line from the derived class to the base class
Abstract members appear in italics

20. Class Diagrams: Interfaces
An interface is a contract and classes implement interfaces
Depict with dotted lines instead of solid lines

21. Class Diagram: Association
A general bi-directional link between classes
Both classes are aware of each other

22. Class Diagram: Aggregation
Remember that aggregation is a special type of association used to model the whole to its parts
Basic aggregation depicted with a hollow diamond
The child instance can outlive the parent instance
Composition depicted with a filled diamond
The child instance cannot outlive the parent instance

23. Relationships: Multiplicity
Relationships also have multiplicity
How object instances are related to other object instance
Symbol
Meaning 1
Attribute has a single value
0..1
Attribute can be null *
A collection of values
1..*
A collection containing at least one value
n..m
A collection containing between n and m values

24. Visibility Object-oriented program supports a notion of visibility
Mark
Visibility
Description +
Public
Visible by other classes and packages #
Protected
Visible to derived types -
Private
Visible only to the owner type ~
Package
Visible to other types in the same package

25. Refactoring This whole process is iterative
And we refine how classes are organized and their attributes