1. Class Diagrams

2. Object, State, Behavior, Identity
Object: An object is a representation of an entity, either real-world or conceptual.
State: State of an object is one of the possible conditions in which it may exist.
open and closed
Behavior: determines how an object responds to requests from other objects and typifies everything the object can do.
add a student and delete a student

3. Class Diagrams The main building block in object oriented modeling
They are used both for general conceptual modeling of the systematics of the application, and for detailed modeling translating the models into programming code
The classes in a diagram represent both the main objects and/or interactions in the application and the objects to be programmed
In the diagram these classes are represented with boxes which contain three parts

4. Class Diagrams
In the system design of a system, a number of classes are identified and grouped together in a class diagram which helps to determine the static relations between those objects
With detailed modeling, the classes of the conceptual design are often split in a number of subclasses
In order to further describe the behavior of systems, these diagrams can be complemented by state diagram or UML state machine
Also instead of class diagrams, Object role modeling can be used if you just want to model the classes and their relationships

5. Class Diagrams A class with three sections.
The upper part holds the name of the class
The middle part contains the attributes of the class
The bottom part gives the methods or operations the class can take or undertake

6. The class icon Defines The class icon has
Persistent system state
System behavior
The class icon has
Name
Attributes
Operations
It’s a rectangle divided into three compartments.

7. Structural Modeling: Core Elements
Reference: OMG tutorial on UML by Cris Kobryn

8. Structural Modeling: Core Elements (cont’d)
¹ An extension mechanism useful for specifying structural elements.
Reference: OMG tutorial on UML by Cris Kobryn

9. Structural Modeling: Core Relationships
Reference: OMG tutorial on UML by Cris Kobryn

10. Structural Modeling: Core Relationships (cont’d)
Reference: OMG tutorial on UML by Cris Kobryn

11. Associations An Association represents a family of links
Binary associations (with two ends) are normally represented as a line, with each end connected to a class box
Higher order associations can be drawn with more than two ends; in such cases, the ends are connected to a central diamond
Fig. 3-40, UML Notation Guide
Reference: OMG tutorial on UML by Cris Kobryn

12. Associations
An association can be named, and the ends of an association can be adorned with role names, ownership indicators, multiplicity, visibility, and other properties
There are five different types of association; bi-directional and uni-directional associations are the most common ones
Fig. 3-40, UML Notation Guide
Reference: OMG tutorial on UML by Cris Kobryn

13. Aggregations
Aggregation is a variant of the "has a" or association relationship; aggregation is more specific than association
It is an association that represents a part-whole or part-of relationship. As a type of association, an aggregation can be named and have the same adornments that an association can
However, an aggregation may not involve more than two classes

14. Aggregations
Aggregation can occur when a class is a collection or container of other classes, but where the contained classes do not have a strong life cycle dependency on the container—essentially, if the container is destroyed, its contents are not
In UML, it is graphically represented as a hollow diamond shape on the containing class end of the tree of lines that connect contained class(es) to the containing class

15. Composition Fig. 3-45, UML Notation Guide
Composition is a stronger variant of the "owns a" or association relationship; composition is more specific than aggregation
Has a strong life cycle dependency between instances of the container class and instances of the contained class(es): If the container is destroyed, normally every instance that it contains is destroyed as well
Note that a part can (where allowed) be removed from a composite before the composite is deleted, and thus not be deleted as part of the composite
The UML graphical representation of a composition relationship is a filled diamond shape on the containing class end of the tree of lines that connect contained class(es) to the containing class
Fig. 3-45, UML Notation Guide
Reference: OMG tutorial on UML by Cris Kobryn

16. Generalization
Indicates that one of the two related classes (the subtype) is considered to be a specialized form of the other (the super type) and supertype is considered as 'Generalization' of subtype
In practice, this means that any instance of the subtype is also an instance of the supertype
An exemplary tree of generalizations of this form is found in binomial nomenclature: human beings are a subtype of simian, which are a subtype of mammal, and so on. The relationship is most easily understood by the phrase 'A is a B' (a human is a mammal, a mammal is an animal).
Fig. 3-47, UML Notation Guide
Reference: OMG tutorial on UML by Cris Kobryn

17. Generalization
The UML graphical representation of a Generalization is a hollow triangle shape on the supertype end of the line (or tree of lines) that connects it to one or more subtypes.
The generalization relationship is also known as the inheritance or "is a" relationship.
The supertype in the generalization relationship is also known as the "parent", superclass, base class, or base type.
The subtype in the specialization relationship is also known as the "child", subclass, derived class, derived type, inheriting class, or inheriting type.
Fig. 3-47, UML Notation Guide
Reference: OMG tutorial on UML by Cris Kobryn

18. Generalization
Note that this relationship bears no resemblance to the biological parent/child relationship: the use of these terms is extremely common, but can be misleading
Generalization-Specialization relationship
A is a type of B
E. g. "an oak is a type of tree", "an automobile is a type of vehicle"
Generalization can only be shown on class diagrams and on Use case diagrams.
Fig. 3-47, UML Notation Guide
Reference: OMG tutorial on UML by Cris Kobryn

19. Dependencies
Dependency is a weaker form of relationship which indicates that one class depends on another because it uses it at some point of time
It exists if a class is a parameter variable or local variable of a method of another class
Fig. 3-50, UML Notation Guide
Reference: OMG tutorial on UML by Cris Kobryn

20. UML Class Diagram Examples
Reference:

26. Object Diagram
A diagram that shows a complete or partial view of the structure of a modeled system at a specific time
Focuses on some particular set of object instances and attributes, and the links between the instances

27. Object Diagram
A set of objects (instances of classes) and their relationships
A static snapshot of a dynamic view of the system
Represents real or prototypical cases
Very useful before developing class diagrams
Worth saving as elaborations of class diagrams

28. Instance Specifications
Each object and link is represented by an Instance Specification
This can show an object's classifier (e.g. an abstract or concrete class) and instance name, as well as attributes and other structural features using slots
Each slot corresponds to a single attribute or feature, and may include a value for that entity

29. Instance Specifications
The name on an instance specification optionally shows …
an instance name, a ':' separator, and optionally one or more classifier names separated by commas
The contents of slots, if any, are included below the names, in a separate attribute compartment
A link is shown as a solid line, and represents an instance of an association

30. Example
As an example, consider one possible way of modeling production of the Fibonacci sequence

31. Example
In the first UML object diagram, the instance in the leftmost instance specification …
is named v1,
has IndependentVariable as its classifier,
plays the NMinus2 role within the FibonacciSystem, and
has a slot for the val attribute with a value of 0

32. Example The second object … is named v2,
is of class IndependentVariable,
plays the NMinus1 role, and
has val = 1

33. Example The DependentVariable object … is named v3, and
plays the N role

34. Example The topmost instance, an anonymous instance specification, …
has FibonacciFunction as its classifier, and
may have an instance name, a role, and slots, but these are not shown here

35. Example The diagram also includes three named links, shown as lines
Links are instances of an association

36. Example
After the first iteration, when n = 3, and f(n-2) = 1, and f(n-1) = 1, then f(n) = = 2
At a slightly later point in time, the IndependentVariable and DependentVariable objects are the same, but the slots for the val attribute have different values
The role names are not shown here

37. Example
After several more iterations, when n = 7, and f(n-2) = 5, and f(n-1) = 8, then f(n) = = 13
In a still later snapshot, the same three objects are involved
Their slots have different values
The instance and role names are not shown here

38. Usage
If you are using a UML modeling tool, you will typically draw object diagrams using some other diagram type, such as on a class diagram
An object instance may be called an instance specification or just an instance
A link between instances is generally referred to as a link
Other UML entities, such as an aggregation or composition symbol (a diamond) may also appear on an object diagram

39. More Examples
Object diagram
Class diagram

40. More Examples
What does this object diagram tell us?

41. More Examples
What would the class diagram look like that goes along with this object diagram?

42. More Examples
Does this make sense to you?

43. More Examples