Quiz
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1. Who is the guru of Extreme Programming?
2. who are the gurus of UML?
3. Do we want highly or lowly cohesive
modules?
4. Do we want strongly or loosely coupled
modules?
What is the principle of Encapsulation?
6. Show the UML diagram for a class
Quiz Answers
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1. Kent Beck
2. Jacobson, Booch, Rumbaugh (Three Amigos)
3. Highly cohesive
4. Loosely coupled
5. The implementation of a module should be
separated from its contractual interface and hidden
from clients.
Point
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6.
-X : int
-Y : int
+move(in dx : int, in dy : int) : void
Point
X
Y
move(dx, dy)
Unified Modeling Language
UML
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Set of graphic notation techniques to create visual
models of software intensive systems
Architectural blueprint of a software system
Capture details about a system such that
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the problem is clearly understood
(design) solution architecture is developed
a chosen implementation is clearly identified and constructed
Provides for ways to express complex relationships among
the basic building blocks
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Those relationships can be static or dynamic
Easier to communicate with non-professionals
Introduction
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Class diagrams
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Shows the static relationships that exist among a group of classes
and interfaces
Common relationships include inheritance (is-a), aggregation (part-of
), dependency and composition
Introduction
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Interaction diagrams
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Used for modeling the dynamic behavior of a system
Two kinds of diagrams one of which are sequence
diagrams (others fall under collaboration diagrams)
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Used for modeling the message exchange between objects in a
system (what do I mean message?)
Capture the relative time ordering of messages exchanges
Introduction
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Other
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State chart diagrams
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Similar to finite state machines
Activity diagrams
Components diagrams
Deployment diagrams
More than12 now
/cond
Use Cases
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Interactions between system and external entities
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Users
Other Systems
What the system does, not how things happen
Specifies a sequence of actions, including variants,
that a system performs and that yields an observable
result of value to a particular actor (Jacobson, Booch,
Rumbaugh)
Use Cases
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Set of scenarios (likely/possible occurrences)
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Main Scenario
Alternative scenarios
Exceptional scenarios
Sequence of interactions between
actors/system
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A little story that outlines some expected sequence of request and
responses between actors and the system
Writing one is a like a game of “what happens next?”
Use Case
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Main Scenario – Normal flow of events and
outcomes
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“what will happen if all the preconditions are met”
Alternatives – also normal
Exceptions – what if preconditions are not met?
Paragraph description of what happens
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“A student registers in a class by logging in (if not
logged in), selecting and open class, and saving the
new schedule”
Use Case
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User: A student
Goal: registers in a class
Scenario: by logging in, (if not logged in),
selecting and open class, and saving the new
schedule
Online Shopping Example
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Name: Validate credit card
Actors: Customer, Credit card company
Main Scenario:
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1. Customer enters credit card number and
expiration date
2. System verifies card with credit card company
3. System sends authorization message to customer
Online Shopping Example
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Alternative 2a: If the credit card company
rejects the card, system sends a rejection
notice
Alternative 2b: If credit card company does not
respond in 10 seconds,
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Tell the user of delay
Repeat verifying the card
Alternative …
General Guidelines
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Use case must define a goal for its user
Must be a “sunny day” scenario
Make at an appropriate level
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not too detailed (trivial, tedious - e.g. login as a
separate use case)
not too high (vague)
Don’t get technical (e.g. reference to specific
DB)
Use Case Diagrams
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Show use cases, actors and their relationships
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Capture the precise requirements for the system from a
user’s perspective (not internal system)
Use Case Diagrams (UML)
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Consists of
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Actors
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A person, organization, or external system that plays a role in one or
more interactions with your system
Can make a service request to the system or be requested to provide
a service
Drawn as stick figures
Use cases (each includes main scenario, alternatives, and
exceptions)
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Scenario
Drawn as ovals
Use Case Diagrams (UML)
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Relationships among actors and use cases
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Generalization relationships among actors
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Association relationships between actors and use cases
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Communication in Visio
Dependency relationships among use cases
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Extends in Visio (change type to inherits) --- could be done in a
separate diagram
Include (Uses in Visio)
 Access account includes login
Extends (i.e. special case of) (Extends in Visio)
 Open a dual account vs. open an account
Last two should be within the System boundary diagram
Sometimes “uses” instead “includes”
University System
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Students, faculty and admins
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Students: Login and get grades
Faculty: Login, view student roster, & enter grades
for a student roster
Admins: Login and verify grades
System
Use Cases
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Every use case in the system must be explicitly described
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Name
Actors involved
Preconditions
Related Use Cases (Uses/Extends)
Main Scenario
Alternative Scenarios
Exceptional Scenarios
Withdraw money from bank via ATM
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Wrong pin
Balance not enough
Money not removed in 60 seconds
Use Cases
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Steps
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Extract actors and use cases
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Draw use case diagram
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Add more relationships, secondary uses cases, secondary actors
Complete
Refine use cases
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Main scenarios
Refine use case diagram
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Main uses cases and actors
Don’t worry about completeness … will refine later on
Describe every use case
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Nouns that perform actions or respond to actions are actors
Verbs or action nouns (registration, enrollment, etc …) are usually use cases
Alternative scenarios
Complete
Iterative development process
E-Book Store
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Allows customers to search and shop for books, music
CDs, and computer software on the Web
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Provides information about the titles it carries to help
customers make purchases
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Other functionalities
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Customer registration (needed for shopping only) – first time only,
login henceforth (needed for shopping only)
Support management of the system such as adding, deleting and
updating titles (Catalog manager)
Updating customer account information & processing orders
(Customer manager)
Manage inventory (Inventory manager) – e.g., order products
E-Book Store
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Actors:
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Customer
Manager
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Inventory
Catalog
Customer
Use Cases:
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Register
Login
Search/Browse
Shop
Manage Inventory
Manage Catalog
Manage Accounts
Manage Orders
«inherits»
«inherits»
User
«inherits»
E-Book Store
«inherits»
Register
Login
«uses»
Browse/Search
*
*
«uses»
Customer
«uses»
«uses»
Manage Catalog
«uses»
«uses»
Shop/Buy
Catalog Manager
Manage Inventory
Manage Accounts
Inventory Manager
Customer Manager
Manage Orders
Use Case: Shop
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Name: Shop
Primary Actor:
Customer
Uses/Extends:
Uses Browse & Login
Precondition:
Customer already
registered
Customer
System
1-Customer searches (Browse)
2-Show info on selected titles
3-Customer selects a title to buy
4-Add to shopping cart
Repeat steps 1 thru 4 as need
5-Done shopping and check out
6-Request customer ID and password
7-Customer enters customer ID
and password (Login) (first time
only)
8-Authenticate customer & Authentication
succeeds
9-Display contents of shopping cart
10-Request shipping address
11-Request payment method and billing address
12-Customer confirms order,
shipping address, payment
method and billing address
13-Validate payment method & Validation
Succeeds
14-Process order, issue receipt and notify
warehouse
Use Case: Shop
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Alternative Scenario 1
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Alternative Scenario 2
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Customer authentication fails  repeat login
procedure (warn user and go back to step 6)
Payment validation fails  prompt the customer for
new payment information (warn user and go back
to step 11)
Exceptional Scenario
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Customer leaves without checking out
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Save shopping cart for 48 hours