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OutlineOutlineIntroduction to UMLObjects and ClassesClass Diagrams
◦Class Icon◦Relationships◦Constraints
UML: Unified Modeling UML: Unified Modeling LanguageLanguage
The Unified Modeling Language (UML) is an industry-standard language for specifying, visualizing, constructing, and documenting the artifacts of software systems
The UML definition was led by Grady Booch, Ivar Jacobson, and Jim Rumbaugh (all now at Rational Software)
Objects and ClassesObjects and ClassesWhat’s object
◦ Identity◦ State◦ Behavior
Sequence Diagram Statechart Diagram
Messages and methodsWhat’s class
◦ Objects and Classes◦ Nature of a class◦ Class Attributes◦ Operation (Method)◦ Interfaces◦ Interfaces and Implementation◦ Corresponding C++ code
ObjectsObjectsConceptually, there are many ways to think
of an object– something that can be seen or touched– a thing to which some action is directed– something that performs a query action
The structure and behaviour of similar objects are defined in their common class
Objects have thee properties: identity , state, and behaviour (query action)
Object Property 1: Object Property 1: IdentityIdentityIdentity is that property of an object which
distinguishes it from all other objectsKeep in mind, however, that an object may
not have a name; Similarly, an object might have multiple names (aliases)– For this reason, there is a subtle distinction
made between the concepts of "name" and "identity"
Object Property 2: StateObject Property 2: State
The state of an object encompasses all of the (usually static) properties of the object plus the current (usually dynamic) values of each of these properties
Object Property 3: Object Property 3: BehaviourBehaviour
Behaviour is how an object acts and reacts, in terms of its status changes and message/information passing
The state of an object represents the cumulative results of its behaviour
Example ObjectsExample ObjectsThere are many physical objects we can
examine right in this room– each person is an object – any chair is not an object– each light bulb is an object– Any book is not an object– this room itself is an object (full or not)
See if the followings are objects or not:◦ Desk◦ Light◦ Person◦ Log◦ The Earth◦ Clock◦ Machine◦ Computer◦ Saving account
Answer: N, Y, Y, N, Y, Y, Y, Y, Y
Objects versus ClassesObjects versus ClassesHow would we describe the state,
behaviour, and identity for each of these objects
We have looked at objects and we have seen that objects can be "classified" into classes
As programmers, we work with both classes and objects from those classes
Classes and ObjectsClasses and ObjectsAn object is called an "instance" of a classThe terms instance and object are
interchangeableCreating an object from a class is often
called instantiationFor example, there are many person objects
in this room -- each person is an instance of the person class
The Nature of a ClassThe Nature of a ClassA class describes the common structure
(attributes/state) and behaviour of its instancesFor example,
– 3.14, 2.71, and 5.5 can be classified as Floats
– the following shapes can be classified as Circles
In a 2D drawing package, circles have a radius, a line thickness, a line color, and a fill color
Each individual circle (instance) drawn by the user has its own value for each attribute
The programmer writes a Circle class and the program instantiates a Circle object every time the user draws a Circle
a snowman made from 9 Circle instances
An attribute is a named property of a class that describes the range of values that instances of the property may hold.(Booch,1999)
An attribute has a type that defines the type of its instances.
Only the object itself should be able to change the value of its attributes.
The values of the attributes define the state of the object
Class AttributesClass Attributes
Operation (Methods)Operation (Methods) An operation is the implementation of a
service that can be requested from any object of the class to affect behavior (Booch, 1999)
An operation can be:– Question (does not change the value of
the object)– Command (may change the value of the
object)
Objectsomething
action
state1 state2action
attribute1 attribute2
operation/method
attributes: {attribute1, attribute2}
operations/methods
value
structure
ReviewReview
Light
On OffTurn on/off
True FalseTurn_on
attributes: {True, False}
operations/methods:
value
structure
Turn_off
Turn_on/off ( )
Class DiagramClass DiagramIntroductionClass IconRelationshipsConstraints
IntroductionIntroduction
The class diagram is fundamental to object-oriented programming
UML’s class diagrams capture the attributes and operations of each class as well the relationships that exist between classes
Class IconClass IconClass IconHiding DetailsVisibility NotationAttribute SpecificationOperation Specification
UML Class IconUML Class Icon The UML class icon is
a rectangle with three compartments:– class name– class attributes– class operations
Attributes are specified in the following form:– object:class name
Circle
radius: float
center_x: int
center_y: int
area()
display()
Hiding DetailHiding Detail
Circle
area()
display()
Circle
radius: float
center_x: int
center_y: int
Circle
You can optionally leave out the attributes, operations, or both in a class icon:
UML Member Visibility UML Member Visibility NotationNotation
UML has three visibility prefixes for members:+ for public, # for protected, and – for private
–e.g.Circle
-radius: float
#area()
+display()
Full UML Attribute Full UML Attribute SpecificationSpecification
The full form of a UML attribute is as follows:[visibility] name [multiplicity] [: type] [= initial value] [{property}]
– The property choices are changeable, addOnly, and frozen
Student Info
-id: string
-hasGraduated: bool = false
Full UML Operation Full UML Operation SpecificationSpecification
The full form of a UML operation is as follows:[visibility] name [(parameter-list)] [:return-type] [{property}]
– The property choices are sequential, concurrent, guarded, and isQuery
The full form of a UML parameter is:[direction] name : type [= default-value]
– The direction choices are in, out, and inout
UML Class RelationshipsUML Class RelationshipsA class relationship is a connection between
two (or more) classesThe three most important class relationships
are generalizations, associations, and aggregations
UML provides a graphical representation for each of the relationships using a different line type for each relationship
Class RelationshipsClass RelationshipsGeneralizationAssociationAssociation ClassQualified AssociationTernary AssociationAggregation
GeneralizationGeneralization A generalization is a relationship between a general
thing (superclass) and a more specific kind of that thing (subclass)
In the UML, generalization requires that objects of the subclass may be used anywhere an object of the superclass appears
Person
Student
AssociationAssociationAn association is a structural relationship that
specifies that objects of one thing are connected to objects of another
Faculty Student
AssociationAssociationAssociations can be adorned with a name.
Faculty StudentTeaching
AssociationAssociationAssociations can be adorned with the roles.
teacherFaculty Studentlearner
AssociationAssociationAssociations can be adorned with the multiplicity.
4..*Faculty Student
1
Association Class (relation Association Class (relation attributes)attributes)
Each object of association class is one instance of relationship (link) in an association.
1..*Faculty Student4..*
Course
Qualified AssociationQualified Association
Qualified association relates two classes and a qualifier.
The qualifier is a special attribute that reduces the effective multiplicity of an association.
Directory Filefile name
Ternary AssociationTernary Association A ternary association is a structural relationship that
specifies that objects of one thing are connected to objects of other two’s.
Developer
LanguageProject
AggregationAggregation
An aggregation is an association that represents whole/part relationship
The “whole” end of the association relationship is adorned with an open diamond shape (e.g. X is part of Y)
e.g. door:Door is part of car:Car
X Y
Generalization, Aggregation, and Generalization, Aggregation, and AssociationAssociation
See if the following pairs of classes have generalization, aggregation or association Faculty & student (as) Hospital & doctor (as) Door & Car (ag --<>) Member & Organization (ag --<>) People & student (ge <|-- ) Circle & point (ge --|>) Department & Faculty (as) Employee & Faculty (ge <|--) Item & Printer (ge <|--) Account & Checking account (ge <|-- )
ConstraintsConstraintsConstraints on ObjectConstraints on Relations
(Ordering)General Constraints (Dependency)
Constraints on ObjectConstraints on ObjectThe constraints restricts the values that objects can be.Example: No employee’s salary can exceed the salary of the employee’s boss.
Employee
Salary
Employer
Salary
{salary <=boss.salary}
Constraints on Relations Constraints on Relations (Ordering)(Ordering)
{Order} indicates that the elements of the “many” end of an association have an explicit order that must be preserved.
Paper Author{ordered}
11..*
General Constraints General Constraints (Dependency)(Dependency)
A dependency is a using relationship that states that a change in specification of one thing may affect another thing that uses it (but not necessarily the reverse)
General Constraints General Constraints (Dependency)(Dependency)
Aerodrome
checkRVR( r: Runway ) Runway
Dependencies are often used when one class uses another class as an argument of the operation
Dependencies are also often used to express general constraints.
Person Committeemember-of
chair-of
{subset}
(Class Name, attribute, method) vs (Table Name, field, query)
(Class & object) vs (Table & row) (Table 1, table 2, … ) vs Knowledge relearning with
OO techniques to quickly locate the information
DesignDesign• Organize the data into “something” (i.e., object) being queried.• Observe the relationship between objects.• Describe the queries into methods, changing, updating, and even deleting the attribute information.• If necessary, translate class, object, attribute value, and method to table, row, field value, and query.
