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CHAPTER TWO
OVERVIEW OF
UML
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Outline
An overview of UML.
Use Case Diagrams
Class Diagrams
Sequence diagrams
State chart diagrams
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UML – Unified modeling language
UML is a pictorial language used to make software blueprints.
The UML is a standard graphical design for presenting important analysis and design concepts
It is used to easily :-
specifying,
visualizing,
Design
constructing of software systems
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Cont..
UML specification defines two major kinds of UML diagram:
Structure diagrams:-
show the static structure of the system and its parts on different abstraction and implementation levels and how they are related to
each other.
The elements in a structure diagram represent the meaningful concepts of a system, and may include abstract, real world and
implementation concepts.
Behavior diagrams:- show the dynamic behavior of the objects in a system, which can be described as a series of
changes to the system over time
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Cont..
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UML Diagrams
Use Case Diagrams
Class Diagrams
Sequence Diagrams
State chart Diagrams
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Use Case Diagrams
It is a dynamic UML diagram used to express behaviour of the system .
It encapsulates the system's functionality by incorporating use cases, actors, and their
relationships.
It is simplest representation that shows :-
the interaction between the system and users
Is shows the relationship between the user and different use cases.
A Use Case diagram consists of
use cases,
Actors
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Actor
it is some one or something outside the system that interacts with the system.
An actor is anything that exchanges data with the system.
An actor can be a user, external hardware, or another system.
Represented as =>
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How to Find Actors
Which is capable to do the following task can be considered as the actor
Supply/use/remove information
Use the functionality.
Will support/maintain the system.
The system’s external resources.
The other systems will need to interact with this one.
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Documenting Actor Characteristics
We should considered the following questions or description
Brief Description for each actors
Why the actor is needed?
What will do the actor in the system?
Actor characteristics might influence how the system is developed
The actor's scope of responsibility.
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Use case
A use case is a list of actions or event steps that helps the achieve the goal of the system .
It is a technique for capturing, modelling and specifying the requirements of a system.
It is represented by oval circle
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How to Find Use Cases
We can find the use case of the system by analyzing the following pointes
What are the system tasks for each actor you have identified?
Does the actor need to be informed about certain occurrences in the system?
Can all features be performed by the use cases you have identified?
What information must be modified or created in the system?
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System boundary
It is rectangle diagram representing the boundary between the actors and the system.
Use Case Diagram(core relationship)
Association: communication between an actor and a use case; Represented by a solid line.
Generalization:
relationship between one general use case and a special use case (used for defining special alternatives)
Represented by a line with a triangular arrow head toward the parent use case.
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Cont.
Include: a dotted line labeled <<include>> beginning at base use case and ending with an arrows pointing to the
include use case.
It occurs when a chunk of behavior is similar across more than one use case
<<include>>
Extend: a dotted line labeled <<extend>> with an arrow toward the base case.
The extending use case may add behavior to the base use case. The base class declares “extension points”.
<<extend>>
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Example: Library management
System
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Use Case Diagrams(cont.)
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Cont.
Pay Bill is a parent use case and Bill Insurance is the child use case. (generalization)
Both Make Appointment and Request Medication include Check Patient Record as a subtask.(include)
The extension point is written inside the base case
Pay bill; the extending class Defer payment adds the behavior of this extension point. (extend)
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Class diagram
Used for describing structure and behavior in the use cases
Provides a conceptual model of the system in terms of entities and their relationships
Used for requirement capture, end-user interaction
Detailed class diagrams are used for developers
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Class representation
Each class is represented by a rectangle subdivided into three compartments
Name
Attributes
Operations
Modifiers are used to indicate visibility of attributes and operations.
‘+’ is used to denote Public visibility (everyone)
‘#’is used to denote Protected visibility (friends and derived)
‘-’is used to denote Private visibility (no one)
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An example of Class
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OO Relationships
There are two kinds of Relationships
Generalization (parent-child relationship)
In generalization, one element is a specialization of another general component. It may be
substituted for it.
It is mostly used to represent inheritance
Association (student enrolls in course)
It is a structural relationship that represents objects can be associated with another object inside the system
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Associations can be further classified as
Aggregation :- an object of one class can own or access the objects of another
E.g. A car needs a wheel to function correctly, but a wheel doesn't always need a car.
Composition:-It is not a standard UML relationship, but it is still used in various applications.
It is a whole/part relationship.
If a composite is deleted, all other
parts associated with it are deleted.
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OO Relationships: Generalization
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OO Relationships: Association
Represent relationship between instances of classes
Student enrolls in a course
Courses have students
Courses have exams Etc.
Association has
Role names (e.g. enrolls)
Multiplicity (e.g. One course can have many students)
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Interaction Diagram
It is a diagram representation used to describe the interactions among different elements or object
The purpose of interaction diagrams is to visualize the interactive behavior of the system.
It shows the flow of messages within a system
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Cont.
The purposes of interaction diagram can be describes as:
To capture dynamic behavior of a system.
To describe the message flow in the system.
To describe structural organization of the objects.
To describe interaction among objects.
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Cont.
The following factors are to be identified clearly before drawing the interaction diagram:
Objects taking part in the interaction.
Message flows among the objects.
The sequence in which the messages are flowing.
This interactive behavior is represented in UML by two diagrams known as
Sequence diagram and
Collaboration diagram
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sequence diagram
it is a type of interaction diagram it describes how and in what order a group of objects works together.
it is known as event diagrams or event scenarios
It is a good way to visualize and validate various runtime scenarios.
It shows different parts of a system work in a ‘sequence’ to get something done
It emphasizes on time sequence of messages
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Basic Sequence Diagram Notations
Class Roles or Participants:-
it describe the way an object will behave in context.
Use the UML object symbol to illustrate class roles, but don't list object attributes.
Activation or Execution Occurrence:-it represent the time an object needs to complete a task.
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Cont..
Self Message: A message an object sends to itself, usually shown as a U shaped arrow pointing back to itself.
Message flow :
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Example :-Sequence Diagram(Telephone call)
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Sequence Diagrams – Object Life Spans
Creation
Create message
Object life starts at that point
Activation
Symbolized by rectangular stripes
Place on the lifeline where object is activated.
Deletion
Placing an ‘X’ on lifeline
Object’s life ends at that point
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State chart Diagrams
A State chart diagram describes a state machine.
State machine is machine which defines different states of an object and these states are controlled by external or internal
events
State chart diagrams are useful to model the reactive systems.
Reactive systems can be defined as a system that responds to external or internal events.
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Cont..
it describes the flow of control from one state to another state.
States are defined as a condition in which an object exists and it changes when some event is triggered.
The most important purpose of State chart diagram is to model lifetime of an object from creation to termination.
It differ from activity diagram is consist of triggered states.
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Cont..
Why we use state chart diagram ?
To model the dynamic aspect of a system.
To model the life time of a reactive system.
To describe different states of an object during its life time.
Define a state machine to model the states of an object.
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Symbols and notation of state chart diagram
Start:-Start state symbol signals the first step of a process.
Transition:-symbol stands for the result of a process
Decision:-Decision were introduced in UML to support
conditionals in activities.
State :-State defines current condition of an event or activity.
End state :-End state symbol stands for the result of a process.
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Cont..
Sample of stat chart diagram
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Cont..
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E.g. login page
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Thank you
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