Fundamentals of Software Engineering

Outline
 What is UML and why we use UML?
 How to use UML diagrams to design
software system?
 What UML Modeling tools we use
today?

What is UML and Why we use UML?
 UML → “Unified Modeling Language”
 Language: express idea, not a methodology
 Modeling: Describing a software system at a high
level of abstraction
 Unified: UML has become a world standard
Object Management Group (OMG): www.omg.org

 More description about UML:
 It is a industry-standard graphical language for specifying, visualizing,
constructing, and documenting the artifacts of software systems
 The UML uses mostly graphical notations to express the OO analysis
and design of software projects.
 Simplifies the complex process of software design

 Why we use UML?
 Use graphical notation: more clearly than natural language
(imprecise) and code (too detailed).
 Help acquire an overall view of a system.
 UML is not dependent on any one language or technology.
 UML moves us from fragmentation to standardization.

1997: UML 1.0, 1.1
1996: UML 0.9 & 0.91
1995: Unified Method 0.8
Other methods
Booch ‘91
Booch ‘93 OMT - 2
OMT - 1
Year Version
2003: UML 2.0
2001: UML 1.4
1999: UML 1.3

How to use UML diagrams to
design software system?
 Types of UML Diagrams:
 Use Case Diagram
 Class Diagram
 Sequence Diagram
 Collaboration Diagram
 State Diagram
This is only a subset of diagrams … but are most widely used

Use-Case Diagrams
 A use-case diagram is a set of use cases
 A use case is a model of the interaction between
 External users of a software product (actors) and
 The software product itself
 More precisely, an actor is a user playing a specific role
 describing a set of user scenarios
 capturing user requirements
 contract between end user and software developers

Use-Case Diagrams
Library System
Borrow
Order Title
Fine Remittance
Client
Employee
Supervisor
Boundary
Actor
Use Case

Use-Case Diagrams
 Actors: A role that a user plays with respect to the system, including human
users and other systems. e.g., inanimate physical objects (e.g. robot); an
external system that needs some information from the current system.
 Use case: A set of scenarios that describing an interaction between a user
and a system, including alternatives.
 System boundary: rectangle diagram representing the boundary between
the actors and the system.

Use-Case Diagrams
 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.

Use-Case Diagrams
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>>
Include: a dotted line labeled <<include>> beginning at base
use case and ending with an arrows pointing to the include use
case. The include relationship occurs when a chunk of
behavior is similar across more than one use case. Use
“include” in stead of copying the description of that behavior.
<<include>>

Use-Case Diagrams
Figure 16.12
The McGraw-Hill Companies, 2005

Use-Case Diagrams
 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)
 Pay Bill is a parent use
case and Bill Insurance
is the child use case.
(generalization)
(TogetherSoft, Inc)

Class diagram
 A class diagram depicts classes and their interrelationships
 Used for describing structure and behavior in the use cases
 Provide 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

Class diagram
 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)
 By default, attributes are hidden and operations are visible.

Class diagram
Account_Name
- Customer_Name
- Balance
+addFunds( )
+withDraw( )
+transfer( )
Name
Attributes
Operations

OO Relationships
 There are two kinds of Relationships
 Generalization (parent-child relationship)
 Association (student enrolls in course)
 Associations can be further classified
as
 Aggregation
 Composition

Subtype2
Supertype
Subtype1
OO Relationships: Generalization
-Inheritance is a required feature of object orientation
-Generalization expresses a parent/child relationship among related classes.
-Used for abstracting details in several layers
Regular
Customer
Loyalty
Customer
CustomerExample:

 Represent relationship between instances of classes
 Student enrolls in a course
 Courses have students
 Courses have exams
 Etc.
 Association has two ends
 Role names (e.g. enrolls)
 Multiplicity (e.g. One course can have many students)
 Navigability (unidirectional, bidirectional)
OO Relationships: Association

Association: Multiplicity and Roles
University Person
1
0..1
*
*
Multiplicity
Symbol Meaning
1 One and only one
0..1 Zero or one
M..N From M to N (natural language)
* From zero to any positive integer
0..* From zero to any positive integer
1..* From one to any positive integer
teacheremployer
Role
Role
“A given university groups many people;
some act as students, others as teachers.
A given student belongs to a single
university; a given teacher may or may not
be working for the university at a particular
time.”
student

Class diagram
[from UML Distilled Third Edition]

Association: Model to Implementation
Class Student {
Course enrolls[4];
}
Class Course {
Student have[];
}
Student Course
enrollshas
* 4

OO Relationships: Composition
Class W
Class P1 Class P2
Association
Models the part–whole relationship
Composition
Also models the part–whole relationship but, in
addition, Every part may belong to only one
whole, and If the whole is deleted, so are the
parts
Example:
A number of different chess boards: Each square
belongs to only one board. If a chess board is
thrown away, all 64 squares on that board go as
well.
Whole Class
Part Classes
Example
Figure 16.7
The McGraw-Hill Companies, 2005
[From Dr.David A. Workman]

OO Relationships: Aggregation
Class C
Class E1 Class E2
AGGREGATION
Container Class
Containee Classes
Bag
Apples Milk
Example
Aggregation:
expresses a relationship among instances of related
classes. It is a specific kind of Container-Containee
relationship.
express a more informal relationship than
composition expresses.
Aggregation is appropriate when Container and
Containees have no special access privileges to
each other.
[From Dr.David A. Workman]

Aggregation vs. Composition
CompositionComposition is really a strong form of association
components have only one owner
components cannot exist independent of their owner
components live or die with their owner
e.g. Each car has an engine that can not be shared with other cars.
Aggregations
may form "part of" the association, but may not be essential to it. They
may also exist independent of the aggregate. e.g. Apples may exist
independent of the bag.

Good Practice: CRC Card
Class Responsibility Collaborator
 easy to describe how classes work by moving cards around; allows to
quickly consider alternatives.

Interaction Diagrams
 show how objects interact with one another
 UML supports two types of interaction
diagrams
 Sequence diagrams
 Collaboration diagrams

Sequence Diagram(make a phone call)
Caller Phone Recipient
Picks up
Dial tone
Dial
Ring notification Ring
Picks up
Hello

Sequence Diagram:Object interaction
Self-CallSelf-Call: A message that an
Object sends to itself.
Condition: indicates when a
message is sent. The message is
sent only if the condition is true.
Iteration
Condition
A B
Synchronous
Asynchronous
Transmission
delayed
Self-Call
[condition] remove()
*[for each] remove()

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.
 Rectangle also denotes when
object is deactivated.
 Deletion
 Placing an ‘X’ on lifeline
 Object’s life ends at that point
Activation bar
A
B
Create
X
Deletion
Return
Lifeline

Sequence Diagram
User Catalog Reservations
1: look up ()
2: title data ()
3: [not available] reserve title ()
4 : title returned ()
5: hold title ()
5 : title available ()
6 : borrow title ()
6 : remove reservation ()
•Sequence diagrams demonstrate the
behavior of objects in a use case by
describing the objects and the
messages they pass.
•The horizontal dimension shows the
objects participating in the interaction.
•The vertical arrangement of
messages indicates their order.
•The labels may contain the seq. # to
indicate concurrency.
Message

Interaction Diagrams: Collaboration diagrams
User
Catalog
Reservations
start
1: look up
2: title data
3 : [not available] reserve title
4 : title returned
5 : hold title
6 : borrow title
6: remove reservation
5: title available
Collaboration diagrams are equivalent to sequence diagrams. All the features of sequence diagrams are
equally applicable to collaboration diagrams
Use a sequence diagram when the transfer of information is the focus of attention
Use a collaboration diagram when concentrating on the classes

State Diagrams (Billing Example)
State Diagrams show the sequences of states an object goes through
during its life cycle in response to stimuli, together with its responses and
actions; an abstraction of all possible behaviors.
Unpaid
Start End
Paid
Invoice created paying Invoice destroying

State Diagrams (Traffic light example)
Yellow
Red
Green
Traffic Light
State
Transition
Event
Start

What UML Modeling tools we use today?
 List of UML tools http://en.wikipedia.org/wiki/List_of_UML_tools
 ArgoUML: http://argouml.tigris.org/
 Rational Rose (www.rational.com) by IBM
 UML Studio 7.1 ( http://www.pragsoft.com/) by Pragsoft Corporation:
Capable of handling very large models (tens of thousands of classes).
Educational License US$ 125.00; Freeware version.
 TogetherSoft Control Center; TogetherSoft Solo (
http://www.borland.com/together/index.html) by Borland

Conclusion
 UML is a standardized specification language
for object modeling
 Several UML diagrams:
 use-case diagram: a number of use cases (use case models the interaction
between actors and software)
 Class diagram: a model of classes showing the static relationships among them
including association and generalization.
 Sequence diagram: shows the way objects interact with one another as
messages are passed between them. Dynamic model
 State diagram: shows states, events that cause transitions between states.
Another dynamic model reflecting the behavior of objects and how they react to
specific event
 There are several UML tools available

Fundamentals of Software Engineering

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Fundamentals of Software Engineering