1. UML Class & Object Diagram I

2. Object-oriented modelling involves classes which function as types that describes their instances which are called objects.
- You look around, and you see one particular chair, a table, a person, and you realize that the objects are related - the person is sitting on the chair by the table.
- A system developed by using the object-oriented technique can be seen as a system consisting of a number of objects which cooperate to solve a task.

3. Object-oriented modelling includes description of: object properties links between objects object behaviour
- You look around, and you see one particular chair, a table, a person, and you realize that the objects are related - the person is sitting on the chair by the table.
- A system developed by using the object-oriented technique can be seen as a system consisting of a number of objects which cooperate to solve a task.

4. Objects Icons representing “real world objects” of different types.
myChair:
:Bus
:Plane
:Truck
:Ship
PN62001:Car
Represented in the UML notation.
Anonymous object, only type is given
Object name and no type
Object name (id) and type
At this moment you have x number of busses, one of them is represented by the buss picture.

5. Classify Objects
Some objects share the same type of qualities so we may formulate a general concept = define a class.
This is a form of abstraction - some of the differences between the objects are “abstracted away” (ignored).
Furniture
myChair:
yourChair:
theBrownSofa:
(a person has a name, the same number of chromosomes, ... )
A class describes a set of objects that have the same type of attributes, behaviour and relationships.

6. Class and Objects UML Notation
Person
SSN
name
address
drive()
Run()
...
class
attributes (fields)
operations
(methods)
class name
person1:Person
SSN =
name= Jane
address=Norway
person2:Person
SSN =
name = James
address = USA
objects
You when you declare the class you select which attributes and operations (behavior) are of interest for your system.
Objects of the given class will have individual values for the specified attributes.

7. Making a Model You are to solves some problem in a domain.
Simplify and find what is essential for your problem.
OO modelling: ”Objects from reality” are mapped ”directly” onto objects in your model.
chair:
car:
Tom:
Seated in
owner
model
mapping
reality

8. Subclass and Superclass
The class of human beings
The subclass of ”female objects”
People is superclass of Female
Jane:
James:
Person
Female
Male
The classes represented in the UML notation.
Person
Female
Male

9. Class Hierarchy ~ Reuse by Inheritance
An employee is a special type of person, so if you already have a Person class and needs an Employee class, then inheritance allows you to reuse class Person.
Person
SSN
name
address
Employee
title
department
An object of type Employee
Jane:Employee
SSN =
name = Jane
address = Norway
title = accountant
department = accounting
inheritance or specialization
Employee is a specialisation
of Person
superclass
subclass
An object of type Employee is also a Person.
An will have all attributes that a Person has plus all of its own.

10. Multiple Inheritance UML and OWL supports multiple inheritance.
Some object-oriented theoreticians claim that multiple inheritance should not be used! (e.g., Java).
Cassette
volume : Integer
Book
CassetteBook
Some times when we describe a new class we see that this new class should have characteristics from two (or more) existing classes. It is then possible to inherit from both classes.

11. One Common Ancestor for All Classes
Object
hashCode
In Java all classes have a common ancestor called Object.
In OWL it is called Thing.
In C++ UML this is not the case.
Person
Car
E.g., common operations: clone(), getClass()
Employee

12. Linking Objects Class Model
Objects are typically connected in some way or another. For example: Jane is married to James, Jane owns a car.
ownership
Person
Car
Class Model
married
association
Object Model (model instance of the class model)
:ownership
Jane:Person
someWreck:Car
Draw associations…
:married
links
James:Person

13. Part-of Relation Some objects can be seen as compost of other objects.
Head 1 1
Arm 1
Person 2 1 2
Leg

14. There Are Typically Many Ways to Classify Objects
Jim may be classified as a person, a male person, an employee, a student and so on - the context decides.
the classes may overlap (or they may be disjoint)
xxx:
Big box could be Person small once could be Male and Employee…

15. How to model gender?

16. Different Models May be Possible!
Person
Gender
Person
gender : String
Gender
Person
Female
Male
Female
Male
Gender
Person ?
Androgyni
Female
Male
Undecided
Big box could be Person small once could be Male and Employee…
Gender
Person
Female
Male
Androgyni

17. Object Behaviour operations ~ behaviour sending a message time
Synchronous and also asynchronous “message passing”…

18. An Object-Oriented Program ------ Objects Work Together and Solve Problems
Objects have identity.
Objects have state, the values of the attributes defines the state. The state change when the values of the attributes change.
Some objects are linked together.
The objects communicate by sending messages to each other (messages follows the links). Sending a message is the same as asking an object to perform one of its operations (methods).

19. Descriptive Models Model describedBy given System E.g. physics :
- the system under study is nature (which is given)
- the mission is to come up with a description (model) that is so good that it can be used to predict and explain natural phenomenon.

20. Specification (Prescriptive) & Descriptive Model
The “specifiedBy role” is a
specialization of the
“describedBy role.”
Model
describedBy
specifiedBy
given
describedBy
specifiedBy
specifies
System
System
In physics the system under study is nature (which
is given); the mission is to come up with a description
(model) that is so good that it can be used to predict
and explain natural phenomenon.
The specification of a software system; the implementation (system) must conform
to the model.
A system is a group of interacting, interrelated, or interdependent elements that form a complex whole.
Person
Car
:Person
:Car 1 *
name
name=“Bob”
:Car
Model
A Model Instance snapshot