Introduction to UML

Class and Object diagrams in UML
(Unified Modeling Language)

http://www.paxcel.net

By:-
Tanjot Singh Sandhu

Paxcel technologies. www.paxcel.net
This is the exclusive property of Paxcel Technologies. This may not be reproduced or given to third parties without their consent.

UML Background

 UML is a standard language for designing and
documenting a system in an object-oriented manner.
 UML includes a set of graphic notation techniques to
create visual models of object-oriented software-
intensive systems.
 The standard is managed, and was created, by the
Object Management Group (OMG).
 UML versions - UML 1.0, 1.1 1.2, 1.3, 1.4, and 1.5
 UML 2.0 – adopted by OMG in 2005.
 UML 2.3 - formally released in May 2010.
 UML 2.4.1 - formally released in August 2011.


Technical aspects of UML
 Building block of UML
Things
 Structural Things (Class, Interface, Collaboration, Use case,
Active class, Component, Node)
 Behavioral things (Message , State)
 Grouping things (Package)
 Annotational things (Notes)

– Relationships
• Dependency (represented as a dashed directed line)
• Association (rendered as solid line)
• Generalization (represented as a solid line with a hollow
arrowhead pointing to the parent)
• Realization (represented as a dashed line with a hollow
arrowhead pointing to the parent)


Technical aspects of UML (Continued)

Diagrams
• Structural/ Static
– Class Diagram
– Object Diagram
– Component Diagram
– Deployment Diagram
• Behavioral/ Dynamic
– Use case Diagram
– Sequence Diagram
– Collaboration Diagram
– Statechart Diagram
– Activity Diagram


Class Diagram
 Class diagram represents a set of classes, interfaces and
their relationships.
 It can be used to model Collaboration of classes,
Database schema.


Class Visibility
Visibility applies to attributes or operations, and specifies
the extent to which other classes can use a given
class‟s attributes or operations.

Three levels of visibility are possible:

1. Public level - usability extends to other classes +
2. Protected level - usability is open only to classes
that
inherit from original class #
3. Private level - only the original


Association in Class diagrams

 By grouping and relating between the classes we create
module and these are termed as Association.
 In order to associate them we need to draw solid arrowed
lines between the classes as shown in the below figure.
 Example – A Person works for a Company.


Association Properties

 Name
Name of the association
 Role
The specific role of the association
 Multiplicity
Indicates the number of objects that are connected
 Type
Plain association, aggregation, composition
 Direction
Direction can also be shown for a association


Association Multiplicity
 One class can be linked to instances of many other
classes.
 That is, it indicates how many objects of one class relate to one
object of another class. It is indicated by a single number or a range
of numbers.
 Thus, multiplicity can be termed as classes having
multiple associations.


Multiplicity Example

 A teacher teaches 1 to 3 courses (subjects).
 Each course is taught by only one teacher.
 A student can take between 1 to 5 courses.
 A course can have 10 to 300 students.


Aggregation Relationships
 Aggregation is a whole/part relationship. In below
example, Window is the whole, and Shape is part of
Window.
 Aggregation is represented with a hollow/ open diamond.
 Ends of a relationship are referred to as its “roles”. Notice
that the role at the Shape end of the aggregation is
marked with a “*”. This indicates that the Window contains
many Shape instances.


Aggregation vs Composition

 Both refer to member object but the existence of member
object (without the containing class or object or after the
lifetime of the containing class or object) makes the
difference.
 Aggregation is also known as a 'has a' relationship
because the containing object has a member object and
the member object can survive or exist without the
enclosing or containing class or can have a meaning after
the lifetime of the enclosing object also.
 Example ('has a'): Room has a table and the table can
exist without the room. The table can have meaning
without the room also.


Aggregation vs Composition (Continued)

 Composition is also known as a 'is a part of' relationship
because the member object is a part of the containing
class.
 Member object cannot survive or exist outside the
enclosing or containing class or does not have a meaning
after the lifetime of the enclosing object.
 Example ('is a part of'): IMEI no. is a part of the Mobile.
IMEI no. cannot exist without the mobile and the IMEI no.
has no meaning after the lifetime of the mobile.


Example - Aggregation vs Composition

 Aggregation

 As you can see, Person does not manage the lifetime of
Address. If Person is destroyed, the Address still exists.


Example - Aggregation vs Composition

 Composition

 If we were going to model a car, it would make sense to
say that an engine is part-of a car.
 Within composition, the lifetime of the part (Engine) is
managed by the whole (Car), in other words, when Car is
destroyed, Engine is destroyed along with it.
 As you can see in the example code above, Car manages
the lifetime of Engine.


Inheritance Relationships

 Depicted by a hollow triangular arrowhead.
 One or more lines proceed from the base of the arrowhead
connecting it to the derived classes.


Dependency Relationships

 Sometimes the relationship between two classes is very
weak. They are not implemented with member variables
at all. Rather they might be implemented as member
function arguments.
 Consider, for example, the Draw function of the Shape
class. Suppose that this function takes an argument of
type DrawingContext.
 Represented as dashed-arrow line.


An abstract class and interface in UML
 Stereotype – Type/ word or string within two surrounding
characters “«»”, called guillemets (pronounced Gee-may).
 Interface is represented by stereotype, «type» in the class
diagram.
 Abstract classes are represented by „{abstract}‟ as shown
in figure.


Some of the commonly used stereo types while writing UML:

<<Application>>:- Used to represent a UI system in a application.
<<Database>> :- represents a database in a application.
<<Table>> :- A table with in database.
<<Library>> :- A reusable library or function.
<<File>> :- Physical file on a folder.
<<Executable>> :- A software component which can be executed.
<<Web services>> :- Represents a web service.
<<JDBC>> :- Java database connectivity , a JAVA API to connect to
database.
<<ODBC>> :- Open database connectivity , a Microsoft API to connect to
database.


Object Diagram
 Class diagrams shows the types and how they are linked.
 Object diagram gives a pictorial representation of class
diagram at any point of time.
 We represent object with Object Name: Class Name.
 Property is represented by „PropertyName=Value‟.
 We can show multiplicity as different objects of same class.
 Other UML entities, such as an aggregation or composition
symbol (a diamond) may also appear on an object diagram.
 Note: - Object diagrams should only be drawn to represent
complicated relationship between objects. It‟s possible that
it can also complicate your technical document as lot. So
use it sparingly.


Object Diagram (Continued)

 Draw an object diagram to illustrate a real-life example of
a class and its relationships.
 Object diagrams can help clarify classes and inheritance
and are sometimes drawn while planning classes.
 Helpful in understanding the system from practical
perspective.
 Assist non-programming stakeholders who may find class
diagrams too abstract.
 An object can also be thought of as the description of an
individual within a group.
 Hence “CheckingAccount” might be defined as a UML
class and “John‟s checking account at Agency Bank”
would be illustrated as an object diagram (on next slide).

Object Diagram... continued

 Object diagrams use notation very similar to class
diagrams.


References
 http://en.wikipedia.org/wiki/Unified_Modeling_Language
 http://www.dotnetfunda.com/articles/article143.aspx
 http://www.dotnetfunda.com/articles/article145.aspx
 http://www.careerride.com/UML-FAQs.aspx
 http://www.objectmentor.com/resources/articles/umlClassDiagrams.pdf
 http://www.altova.com/umodel/object-diagrams.html
 http://design-antony.blogspot.in/2007/07/aggregation-vs-composition.html
 http://www.c-
sharpcorner.com/UploadFile/pcurnow/compagg07272007062838AM/compagg.asp
x


Introduction to UML

More Related Content

What's hot

Viewers also liked

Similar to Introduction to UML

More from Paxcel Technologies

Recently uploaded

Introduction to UML