Chapter 25 - The Unified Modeling Language

Chapter Goals

To continue the exploration of the UML
To understand the creation and application of cases
To learn how to create and use the various diagram types in the UML
To understand how sequence diagrams help document the dynamic relationships between classes

25.1 Graphical Notation

Convey design information
Relationship information easily extracted
The following scale better than flowcharts:
- Object diagrams (chptr. 10)
- Class diagrams (chptr. 11)
- CRC cards (chptr. 13)
To follow: wider variety of class, sequence, and state diagrams, and use cases

25.2 Use Cases

Describe how a system should work
Each case:
- Focuses on a specific scenario
- Describes steps to completion
Each step represents an interaction between an outside entity (actor) and the system
Use case must complete to a point that is of some value

25.2 Use Cases

E.g., a voice mail system:

"Leave a message" - steps a caller (the actor) must take
- Value: actor deposits a message
"Retrieve messages" - steps the mailbox owner must take
- Value: actor retrieves his messages

25.2 Use Cases

A use case should have:
- Descriptive name
- Main sequence of actions
- Variants
  - Description of possible failures
Can be made simple or formal

25.2 Use Cases - E.g.

Leave a Message:

Caller dials mail system
System prompts for mailbox:
Enter mailbox #
Caller enters recipient's extension
System prompts for message:
Leave message for xxx
Caller speaks message
Caller hangs up
System stores message in recipient's mailbox

25.2 Use Cases - E.g. (cont.)

Variation #1:

1.1	User enters invalid extension (Step 3)
1.2	System responds `Invalid mailbox #`
1.3	Continue with Step 2

Variation #2:

2.1	Caller doesn't leave a message (after Step 4)
2.2	System discards empty message

25.3 UML Class Diagrams

Static
Describe class relationships
Classes drawn as boxes
Appropriate attributes and methods in additional compartments:

25.3 UML Class Diagrams (cont.)

Important attributes and methods are listed
Type of attributes and parameters can be specified attribute : Type

text : string
Similarly for return type of methods:
get_message(index : int) : Message
Types often omitted for attributes, parameters, and return values

25.3 UML Class Diagrams (cont.)

Links (connectors) for class diagrams:

25.3 UML Class Diagrams (cont.)

Denote multiplicity at the endpts. of the aggregation connector
Common notations:

* zero or more

1..* one or more

0..1 zero or one

1 exactly one

25.3 UML Class Diagrams (cont.)

Enclosing class contains arrow tip
A queue may have 0 or more messages
A message will be on exactly one queue

25.3 UML Class Diagrams (cont.)

Composition - stronger form of aggregation
Contained objects do not exist independently
A solid diamond is used
A message queue is permanently contained in a mailbox:
But messages are not specific to a given queue

25.3 UML Class Diagrams (cont.)

An association is a more general relationship
Used early in the design
Solid line w/no diamond
Roles can be written at the ends of the lines:
Students register for courses, courses have students
Bidirectional

25.3 UML Class Diagrams (cont.)

Associations are often directed
E.g., messages know nothing about the containing queue:
Use open arrow
Try to minimize dependencies

25.4 Sequence Diagrams

Show dynamics of a scenario
Describe communications among objects
Most commonly illustrates the behavior of a single method

25.4 Sequence Diagrams (cont.)

E.g., adding a message to a mailbox. The mailbox adds it to its new-message queue:
new_messages.add(...)

25.4 Sequence Diagrams (cont.)

Objects are boxes w/underlined text
Text might be:
- object_name : ClassName
- object_name
- : ClassName
Dashed vertical line is the lifeline

Used to sequence events

Rectangles are activation bars

Object is executing a method (or waiting)

Arguments are not listed

25.4 Sequence Diagrams (cont.)

A method called on the same object:

25.4 Sequence Diagrams (cont.)

Use <<create>> to denote the creation of a heap object:

25.4 Sequence Diagrams (cont.)

Omit a large amount of detail
Generally omit branches and loops (though notation is defined)
Just show the principal objects and order of calls
Can document complex interactions

Common when a limited object collaborates w/several others

25.5 State Diagrams

Describe a discrete set of states that affect behavior
Lists the transitions (some event) between the states
E.g., to retrieve recent messages, user must
- Enter mailbox #
- Enter passcode
- Enter menu command

25.6 Case Study: A Voice Mail System

Simulation of a simple voice mail system
3 events:
- Press a button - a single numeric character ('#' denotes end of sequence)
- Hang up - 'H' by itself
- Speak - any other input
Analysis phase: first formal step

Define behavior of system through use cases
Not a full spec (limitations, performance, etc.)

25.6.1 Use Cases for the Voice Mail System

Reach an Extension

The caller dials main # of system
System speaks prompt:
Enter mailbox number followed by #
Caller enters number of recipient
System speaks:
You have reached mailbox xxxx. Please leave message.

25.6.1 Use Cases for the Voice Mail System (cont.)

Leave a Message

Caller Reaches an Extension
Caller speaks msg
Caller hangs up
System places msg in recipient's mailbox

25.6.1 Use Cases for the Voice Mail System (cont.)

Log in

Mailbox owner Reaches an Extension
Owner enters the passcode, followed by # key. (Default passcode same as mailbox number. Owner may Change the Passcode)
System plays mailbox menu:
Enter 1 to retrieve your msgs Enter 2 to change your passcode Enter 3 to change your greeting

25.6.1 Use Cases for the Voice Mail System (cont.)

Retrieve Messages

Owner Logs in
Owner selects "retrieve msgs" option
System speaks msg menu:
Enter 1 to listen to current msg Enter 2 to save current msg Enter 3 to delete current msg Enter 4 to return to mailbox menu

25.6.1 Use Cases for the Voice Mail System (cont.)

Retrieve Messages (cont.)

Owner selects "listen to current msg" option
System plays current new msg; if none exists, plays current old msg. Neither queue is changed
System speaks msg menu
Owner selects "delete current msg" option. Msg permanently removed
Go back to Step 3

25.6.1 Use Cases for the Voice Mail System (cont.)

Variation #I. Saving a message

1.1	Start at Step 6
1.2	Owner selects "`save current msg`". Msg is removed from its queue, added to queue of old msgs.
1.3	Go back to Step 3

25.6.1 Use Cases for the Voice Mail System (cont.)

Change the Greeting

Owner Logs in
Owner selects "change your greeting" option
Owner speaks the greeting
Owner presses the # key
System sets the new greeting

25.6.1 Use Cases for the Voice Mail System (cont.)

Variation #I. Hang up before confirmation

1.1	Start at Step 3
1.2	Owner hangs up (disconnects)
1.3	System keeps old greeting

25.6.1 Use Cases for the Voice Mail System (cont.)

Change the Passcode

Owner Logs in
Owner selects "change your passcode" option
Owner types new passcode
Owner presses the # key
System sets the new passcode

25.6.1 Use Cases for the Voice Mail System (cont.)

Variation #I. Hang up before confirmation

1.1	Start at Step 3
1.2	Owner hangs up (disconnects)
1.3	System keeps old passcode

25.6.2 CRC Cards for the Voice Mail System

Discover classes
Nouns from the functional specification:
- Mailbox
- Message
- MailSystem

25.6.2 CRC Cards for the Voice Mail System (cont.)

`Mailbox`

Keeps messages
Track new vs. saved msgs
Messages can be
- Deposited in mailbox
- Retrieved
- Saved
- Deleted
Need FIFO - use queues
New vs. saved - use 2 queues
CRCs, so far:

25.6.2 CRC Cards for the Voice Mail System (cont.)

`MailSystem`

Need a class to manage mailboxes:

25.6.2 CRC Cards for the Voice Mail System (cont.)

`Telephone` (simulation)

Take user input
Play (display) output on speaker

25.6.2 CRC Cards for the Voice Mail System (cont.)

`Connection`

Multiple phones connected to system
Each connection keeps track of current state
Create a separate class, to avoid bogging down system
Driver responsible for creation of Telephone, MailSystem, and Connection

25.6.2 CRC Cards for the Voice Mail System (cont.)

Leave a Msg use case - simple scenario walkthrough

User types an extension:
- Telephone sends number to Connection
- Connection collaborator of Telephone
- Place the 2 cards adjacent)
Connection asks MailSystem to find appropriate MailBox object
- Vaguely included in the "manage mailboxes" responsibility
- Keep MailSystem and Mailbox cards close to Connection card
Connection asks Mailbox for its greeting
- Add "manage greeting" to Mailbox responsibilities
- add Mailbox as a collaborator of Connection

(cont.)

25.6.2 CRC Cards for the Voice Mail System (cont.)

Leave a Msg use case (cont.)

Connection asks Telephone to play greeting
User speaks the msg:
- Telephone asks Connection to record it
- Add "record voice input" responsibility to Connection
User hangs up:
- Telephone notifies Connection
Connection wraps the msg in a Message object
- Add Message as a collaborator of Connection
- Make a Message card with responsibility "manage msg contents"
The Connection adds the Message object to MailBox

25.6.2 CRC Cards for the Voice Mail System (cont.)

25.6.2 CRC Cards for the Voice Mail System (cont.)

Retrieve Messages use case

First few steps same as preceding.

User types passcode
- Telephone notifies Connection
Connection asks Mailbox to check passcode
- Add "manage passcode" responsibility to Mailbox
If passcode valid:
- Connection sets the Mailbox as current
- asks Telephone to speak mailbox menu

25.6.2 CRC Cards for the Voice Mail System (cont.)

Retrieve Messages use case (cont.)

User chooses "retrieve msgs" option
- Telephone passes it on to Connection
Connection asks Telephone to speak msg menu
User types in the "listen to current message" option
- Telephone passes it on to the Connection
Connection gets first Message from current Mailbox
- sends its contents to the Telephone
- Add "retrieve messages" responsibility to Mailbox)

25.6.2 CRC Cards for the Voice Mail System (cont.)

Retrieve Messages use case (cont.)

Connection asks the Telephone to speak the message menu
User types in "save current message" option

The Telephone passes it on to the Connection

Connection tells the Mailbox to save current msg
- Modify the responsibilities of Mailbox to retrieve, save, delete messages)
The Connection asks the Telephone to speak the message menu

25.6.2 CRC Cards for the Voice Mail System (cont.)

The updated Mailbox CRC:
Remaining use cases do not add new information, hence, omitted

25.6.2 CRC Cards for the Voice Mail System (cont.)

High level reasoning is difficult
Easily-implemented operations vs. those that appear easy
Practice
Many false starts and detours
Redesign until system works
CRC cards are meant to fail early, often, and inexpensively
Plan to trash your first design
Practice

25.6.3 UML Class Diagrams for the Voice Mail System

Collaboration parts of the CRC cards show dependencies:
- Mailbox depends on MessageQueue
- MailSystem depends on Mailbox
- Connection depends on Telephone, MailSystem, Message, and Mailbox
- Telephone depends on Connection

25.6.3 UML Class Diagrams for the Voice Mail System

Aggregation:
- System has mailboxes
- Mailbox has 2 msg queues
- Queue has msgs (maybe)
- A Connection has a current mailbox; also references to the MailSystem and Telephone objects
No inheritance
Note: aggregation implies dependency

25.6.3 UML Class Diagrams for the Voice Mail System

25.6.4 UML Sequence and State Diagrams

Understand complex control flow w/multiple objects
Telephone reads input
Passes it to Connection
Postulate 3 functions for Connection:
- dial - passes on button press
- record - passes on speech
- hangup - tells connection telephone has hung up

25.6.4 UML Sequence and State Diagrams (cont.)

Leave a Message sequence diagram

25.6.4 UML Sequence and State Diagrams (cont.)

Leave a Message sequence diagram

Caller keys in extension (shown as single call to dial)
Connection calls system's find_mailbox
The Mailbox object on the right is returned
Connection invokes get_greeting
(greeting is passive; doesn't appear on diagram)
Connection plays appropriate greeting
Telephone reads msg from user, passes it to connection
Telephone reads hangup, passes it to connection
Connection constructs Message, adds it to mailbox

25.6.4 UML Sequence and State Diagrams (cont.)

Retrieve a Message sequence diagram

25.6.4 UML Sequence and State Diagrams (cont.)

System is not in control of input
Telephone notifies connection of any input event
E.g., connection is called 3 times during Leave a Msg
The connection must keep track of states, to determine proper action on given input
Next slide is the state diagram for the system

25.6.4 UML Sequence and State Diagrams (cont.)

25.6.5 Implementation

Following files can be downloaded and run
Enter Q to quit
Look at the classes
Compare documentation to the CRC cards and UML diagrams
Trace functions calls, compare to the sequence diagrams
Find the state transitions for Connection
Only modify Telephone and MailSystemTest to add a GUI (chptr 27)

25.6.5 Implementation (`message.h`)

25.6.5 Implementation (`mailbox.h`)

25.6.5 Implementation (`mailbox.cpp`)

25.6.5 Implementation (`mailsystem.h`)

25.6.5 Implementation (`mailsystem.cpp`)

25.6.5 Implementation (`telephone.h`)

25.6.5 Implementation (`telephone.cpp`)

25.6.5 Implementation (`connection.h`)

25.6.5 Implementation (`connection.cpp`)

25.6.5 Implementation (`mailsystemtest.cpp`)

Chapter Summary

Graphical notations help convey design information
Use cases provide concrete scenarios from which general action can be abstracted
Class diagrams record various relationships, including use, dependency, and inheritance
Sequence diagrams record the dynamic interaction between objects
State diagrams are useful for documenting objects that change their behavior during the course of execution according to their current state

`*`	zero or more
`1..*`	one or more
`0..1`	zero or one
`1`	exactly one

Chapter 25 - The Unified Modeling Language

Chapter Goals

25.1 Graphical Notation

25.2 Use Cases

25.2 Use Cases

25.2 Use Cases

25.2 Use Cases - E.g.

Leave a Message:

25.2 Use Cases - E.g. (cont.)

Variation #1:

Variation #2:

25.3 UML Class Diagrams

25.3 UML Class Diagrams (cont.)

25.3 UML Class Diagrams (cont.)

25.3 UML Class Diagrams (cont.)

25.3 UML Class Diagrams (cont.)

25.3 UML Class Diagrams (cont.)

25.3 UML Class Diagrams (cont.)

25.3 UML Class Diagrams (cont.)

25.4 Sequence Diagrams

25.4 Sequence Diagrams (cont.)

25.4 Sequence Diagrams (cont.)

25.4 Sequence Diagrams (cont.)

25.4 Sequence Diagrams (cont.)

25.4 Sequence Diagrams (cont.)

25.5 State Diagrams

25.6 Case Study: A Voice Mail System

25.6.1 Use Cases for the Voice Mail System

Reach an Extension

25.6.1 Use Cases for the Voice Mail System (cont.)

Leave a Message

25.6.1 Use Cases for the Voice Mail System (cont.)

Log in

25.6.1 Use Cases for the Voice Mail System (cont.)

Retrieve Messages

25.6.1 Use Cases for the Voice Mail System (cont.)

Retrieve Messages (cont.)

25.6.1 Use Cases for the Voice Mail System (cont.)

Variation #I. Saving a message

25.6.1 Use Cases for the Voice Mail System (cont.)

Change the Greeting

25.6.1 Use Cases for the Voice Mail System (cont.)

Variation #I. Hang up before confirmation

25.6.1 Use Cases for the Voice Mail System (cont.)

Change the Passcode

25.6.1 Use Cases for the Voice Mail System (cont.)

Variation #I. Hang up before confirmation

25.6.2 CRC Cards for the Voice Mail System

25.6.2 CRC Cards for the Voice Mail System (cont.)

Mailbox

25.6.2 CRC Cards for the Voice Mail System (cont.)

25.6.2 CRC Cards for the Voice Mail System (cont.)

MailSystem

25.6.2 CRC Cards for the Voice Mail System (cont.)

Telephone (simulation)

25.6.2 CRC Cards for the Voice Mail System (cont.)

Connection

25.6.2 CRC Cards for the Voice Mail System (cont.)

Leave a Msg use case - simple scenario walkthrough

25.6.2 CRC Cards for the Voice Mail System (cont.)

Leave a Msg use case (cont.)

25.6.2 CRC Cards for the Voice Mail System (cont.)

25.6.2 CRC Cards for the Voice Mail System (cont.)

Retrieve Messages use case

25.6.2 CRC Cards for the Voice Mail System (cont.)

Retrieve Messages use case (cont.)

25.6.2 CRC Cards for the Voice Mail System (cont.)

Retrieve Messages use case (cont.)

25.6.2 CRC Cards for the Voice Mail System (cont.)

25.6.2 CRC Cards for the Voice Mail System (cont.)

25.6.3 UML Class Diagrams for the Voice Mail System

25.6.3 UML Class Diagrams for the Voice Mail System

25.6.3 UML Class Diagrams for the Voice Mail System

25.6.3 UML Class Diagrams for the Voice Mail System

25.6.4 UML Sequence and State Diagrams

25.6.4 UML Sequence and State Diagrams (cont.)

Leave a Message sequence diagram

25.6.4 UML Sequence and State Diagrams (cont.)

Leave a Message sequence diagram

25.6.4 UML Sequence and State Diagrams (cont.)

`Mailbox`

`MailSystem`

`Telephone` (simulation)

`Connection`

25.6.5 Implementation (`message.h`)

25.6.5 Implementation (`mailbox.h`)

25.6.5 Implementation (`mailbox.cpp`)

25.6.5 Implementation (`mailsystem.h`)

25.6.5 Implementation (`mailsystem.cpp`)

25.6.5 Implementation (`telephone.h`)

25.6.5 Implementation (`telephone.cpp`)

25.6.5 Implementation (`connection.h`)

25.6.5 Implementation (`connection.cpp`)

25.6.5 Implementation (`mailsystemtest.cpp`)