Introduction to UML
SOFTWARE ENGINEERING
BIT-8
APRIL, 16,2008
Agenda
 Part 1:
 Why modeling?
 Introduction to Unified Modeling Language.
 Uses of UML
 Mapping Diagrams.
 Part 2:
 Use-Case Diagrams
 Actors/Use-cases
 Part 3:
 Lab-Task: Case Study
Modeling
 A model is a simplified representation of a
complex reality.
 Complex systems and software cannot be
understood without properly modeling them.
 Today, software are getting complex and
consequently we need to understand them
through modeling.
Modeling
 In simple words, we need simpler representations for
complex models and modeling is a mean for dealing
with complexity.
 A modeling method comprises a language and also a
procedure for using the language to construct models.
 Modeling is the only way to visualize your design and
check it against requirements before you start to code.
Unified Modeling Language (UML)
 UML is a notational system which is principally
graphical and aims at modeling system using object
oriented concepts.
 UML is termed as a “Visual Modeling Language’.
 Generally UML is used for modeling software systems.
 UML consists of :
Views: shows different faces of the system and links with the process
 Diagrams: are basically the graphs that explain the contents of view.
 Model Elements: are contained within the diagrams.

Unified Modeling Language
 UML is a complete language for capturing knowledge
about a subject and then expressing that knowledge
i.e. gathering requirements and then modeling those
requirements.
 Such modeling includes two phases :
Analysis
Design
Unified Modeling Language
UML
Analysis Phase:
•System is described by a set
of requirements.
•USE-CASE DIAGRAM
Design Phase:
•It is tightly connected to the
analysis phase, as it starts
from the identification of
requirements and continues
up till the detailed
specification of those
requirements.
•Class Diagrams
•Interaction Diagrams
•State Chart Diagrams
•Deployment Diagrams
USE-CASE DIAGRAMS
SOFTWARE ENGINEERING
BIT-8
Use-Case Diagram
 Use
Case Diagram is used to describe the
functionalities provided by a system and the users
associated with that system.
 The Use case diagram is used to identify the primary
elements and processes that form the system.
 The primary elements are termed as "actors" and the
processes are called "use cases."
 The Use case diagram shows which actors interact with
each use case.
Use-Case Diagram
 The main purpose of the use-case diagram is:

to help development
requirements of a system

To help identify relationship of "actors" (human beings who will
interact with the system) with essential processes

teams
visualize
the
functional
and understand the relationships among different use cases
Elements of a use-case diagram
 Use-case diagrams contain the following
elements:
• Actors, which represent users of a system,
including human users and other systems.
• Use Cases, which represent functionality or
services provided by a system to users.
Actor
 Definition:
 The outside entity which communicates with the system:
 A Person (user)
 An external system
 Physical Environment
 An Actor has a unique name and an optional description
 Symbol:
UML notation used to represent an actor
Actor (Example)
 Consider the following scenario related to a
“University Management System” :


In a university management system, a Student can submit the
assignments, the instructor marks those assignments and
then uploads the result. The Student is allowed to view the
Results.
Now, by recalling the definition of actor, can you identify the
actors in this System?
 Student
 Instructor
Actor (Example/2)
Instructor
Student
Student
Student is an external
entity which interacts
with the system. Student
is a user of this system,
as some services are
used by it.
Instructor
Instructor is another
external entity which
interacts
with
the
university management
system.
Use-case
 Represent functionality or services provided by a
system to users.
 It is a description of set of sequence of actions that a
system perform that produces an observable result.
 A use case represents a class of functionality provided
by the system as an event flow.
 Use cases describe the interaction between a primary
actor and the system itself
Use-case
 The use case technique is used in software and systems
engineering to capture the functional requirements of a
system.
 Each use case describes how the actor will interact with
the system to achieve a specific goal.
 One or more scenarios may be generated from each
use case, corresponding to the detail of each possible
way of achieving that goal.
 Symbol :
UML notation used to represent a use-case
Use-case (Example)
 Consider the same example again:
 In a university management system, a Student can submit the
assignments, the instructor marks those assignments and then
uploads the result. The Student is allowed to view the Results.
 Now, by recalling the definition of use-case, can you identify
the use-cases in this System?
 Submit Assignments
 Mark Assignments
 Upload Results
 View Results
Use-case (Example/2)
 The use-cases are linked with the functional
requirements of this system. In this example :
Student submit the assignments.
 Instructor marks the assignments.
 Instructor upload the marks.
 Student can view the marks.

 It is now clear that how actors are interacting with
different use-cases of this system.
 Now, lets combine actors and use-cases in one
diagram? Easy ?
Symbols in Use-Case Diagrams
ACTOR
USE-CASE
INTERACTION:
denotes set of messages exchanged among objects
NOTES/COMMENTS
Use-Case Diagram (University Management System)
Submit
Assignments
Mark
Assignments
Student
Upload
Results
View Results
Instructor
Package:
University Management System
SYSTEM
BOUNDARY
Extending Use-Case Diagram
SOFTWARE ENGINEERING
BIT-8
Lab-Exercise
(Extracting Use-cases)
1 HOUR EXERCISE
Use-Case Associations
 Use case association is the relationship between use
cases
 Important types:
 Extends
 A use

case extends another use case
Include
 A use
case uses another use case (“functional
decomposition”)
<<Include>>: Functional Decomposition
 A function in the original problem statement is too
complex to be solved immediately.
 What’s the Solution?
 Describe the function as the aggregation of a set of simpler functions
 The associated use case is decomposed into smaller use cases
<<include>> Example
 The include association from Use Case A to Use Case B
indicates that an instance of A performs all the
behavior described in B
Base
(A)
<<include>>
Supplier (B)
 In <<include>> association, the base case cannot exist
alone. It is always called with the supplier use case
<<Extend>> Association for Use Cases
 Problem:

The functionality in the original problem statement needs to
be extended.
 Solution:

An extend association from Use Case B to Use Case A indicates
that B is an extension of A.
A
<<extend>>
B
Example
 Example:
 The
use case “ReportEmergency” is complete by itself
, but can be extended by the use case “Help” for a
specific scenario in which the user requires help
 Note: In an extend association, the base use case can
be executed without the use case extension
<<extend>>
ReportEmergency
Field Officer
Help
Lab-Exercise
 Read the following case :



Identify the actors
Identify (extract ) the use cases
Construct a proper use-case diagram (with proper symbols &
notations)
Case-Study
 Consider the Library Management System of SEECS. A
Student is allowed to issue books for a period of two
weeks. Student can read newspapers/magazines in the
library and can even access the databases for e-books.
The Library Staff is responsible for maintaining the
records of students and along with the issued books. The
Staff marks an entry in the register whenever a student
issue or return a book. A fine is charged on a student if
he/she fail to return the book on time. The Librarian is
there to manage the staff, check the records and prepare
reports for DG/DEAN.