Class and Object diagrams in UML (Unified Modeling Language)

1. Class and Object diagrams in UML
(Unified Modeling Language)
http://www.paxcel.net
By:-
Tanjot Singh Sandhu
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2. 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.
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3. 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)
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4. 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
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5. Class Diagram
 Class diagram represents a set of classes, interfaces and
their relationships.
 It can be used to model Collaboration of classes,
Database schema.
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6. 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
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7. 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.
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8. 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
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9. 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.
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10. 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.
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11. 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.
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12. 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.
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13. 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.
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14. 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.
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15. 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.
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16. 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.
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17. 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.
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18. 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.
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19. 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.
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20. 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.
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21. 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.
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22. 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).
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23. Object Diagram... continued
 Object diagrams use notation very similar to class
diagrams.
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24. 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
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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.