Topics for week 3

1
The Object-oriented Paradigm and The Unified
Modeling Language (UML)
2
Problems of software development

• "problems" of software development (review)
• conceptual integrity
• incremental build, progressive refinement
• large projects "differ" from small ones
• programming paradigms (1950s-present) attempts
  to deal effectively with these problems, make
  software easier to develop and to maintain

3
Languages and design methodology
Computer Language / Design Methodology brief
history 1950'sunstructured, no information
hiding--spaghetti code, GOTO,
flowcharts --machine code --assembly lang.
--FORTRAN, LISP (Algol COBOL) 1980s
structured, top-down design (3 basic control
structures, no GOTO), modularity --Pascal --(C)
--Ada 1990s encapsulation,
information-hiding, reuse, hardware/software
codesign --C --Java 2000s info
hiding web languages environments encapsulating
multiple languages, styles --.NET --Python --MA
TLAB
4
OO class
Important basic OO concepts class
encapsulates data structure (object)
and associated methods (functions)
these may be declared public / private /
protected appropriate uses public pass info
to object or request info about object (use
"messages") (can be used by anyone) private
modify object (can be used in class or by
friends) protected for descendants (in class
or by derived class and friends)
5
Record/class
traditional record (struct) functions to use
or modify this record can be anywhere
in the program OO class concept supports
encapsulation, information hiding
OO Prog.
DATA
DATA
DATA
DATA
DATA
DATA
DATA
Procedural Prog.
6
Inheritance
Ex Object data structures A. Base class B.
Derived class
X Y Z W
X Y Z
A.
B.
Useful OO techniques Inheritance ex in a
program modeling an ecosystem, we might have the
relationships wolf is carnivore sheep is
herbivore grass is plant carnivore is animal
herbivore is animal animal is organism plant is
organism here the base class organism holds
data fields which apply to all organisms, e.g.,
amount of water needed to survive two derived
classes, plant and animal, hold information
specific to each of these types of organisms,
e.g., kind of soil preferred by plant the animal
class also has two derived classes, wolf and
sheep Inheritance allows the collection of
common attributes and methods in "base" class and
inclusion of more specific attributes and methods
in derived classes
7
Polymorphism and overloading
Polymorphism base class can define a
virtual function appropriate versions of this
function can be instantiated in each derived
class (e.g., "draw" in the base class of
graphical objects can have its own specific
meaning for rectangles, lines, ellipses) Overload
ing ex cin gtgt num1 gtgt is overloaded
"shift ex can be overloaded to allow the
addition of two vectors ex a function name can
be overloaded to apply to more than one
situation e.g., a constructor can be defined one
way if initial values are given and a different
way if initial values are not given
8
Templates
Templates example template ltclass Tgt T
method1 (T x) .. can be specialized int
method1 (int x) float method1 (float
y) usertype method1 (usertype a) templates
promote reuse
9
Separate compilation

• Separate compilation
• Typically, an object-oriented program can be
  broken into three sets of components
• definitions and prototypes (text files, header
  files)
• implementations (compiled--source code need not
  be available to user)
• application program--uses the classes defined in
  header files and supported by the implementation
  files
• This strategy promotes reuse and information
  hiding

10
Misuse of object-oriented paradigm
Note no paradigm is misuse-proof
11
Using OO UML in quarter project
Developing an OO project we will use UML
(subset) determine specifications use
cases determine classes and connections (static
behavior) ER or class diagrams CRC
cards model dynamic behavior interaction
(object message) diagrams activity
diagrams state diagrams sequence diagrams
12
UML a language for specifying and designing an
OO project
UML stands for "unified modeling
language unifies methods of Booch, Rumbaugh
(OMT or Object Modeling Technique), and Jacobson
(OOSE or Object-Oriented Software
Engineering) mainly a modeling language, not a
complete development method Early versions --
second half of the 90's Not all methods we will
use are officially part of the UML description
13
Use cases
USE CASES a part of the Unified Modeling
Language" (UML) which we will use for
requirements analysis and specification each
identifies a way the system will be used and the
"actors" (people or devices) that will use it (an
interaction between the user and the
system) each use case should capture some
user-visible function and achieve some discrete
goal for the user an actual user can have many
actor roles in these use cases an instance of a
use case is usually called a "scenario Use case
will typically have graphical verbal forms
14
Example use case
Example cellular network place and receive calls
use case (based on Booch, Rumbaugh, and
Jacobson, The Unified Modeling Language User
Guide)
Text description --Use case name (cellular
network place and receive calls) --Participat
ing actors (cellular network and human
user) --Flow of events (network or user
accesses network to use its
functionality) --Entry condition(s) (user
accesses network using device or password)
--Exit condition(s) (call completed lost
or network busy) --Quality requirements
(speed, service quality)
System boundary
Use case diagramsummarizes, provides system
overview
Text descriptiongives important details
15
use case
Text description Use case name Participating
actors Flow of events Entry condition(s) Exit
condition(s) Quality requirements
16
Use casedetailed example (Pressman)

• Example SAFEHOME system (Pressman)
• Use case InitiateMonitoring
• (Pressman text categories
• Primary actor (1)
• Goal in context (2)
• Preconditions (3)
• Trigger (4)
• Scenario (5)
• Exceptions (6)
• Priority (system development) (7)
• When available (8)
• Frequency of use (9)
• Channel to actor (10)
• Secondary actors (11)
• Channels to secondary actors (12)
• Open issues (13) )

Homeowner
Accesses system via internet
Sensors
System administrator
Reconfigures sensors and related system
features
Pressman, p. 163, Figure 7.3
17
Use casedetailed example (Pressman)
Example SAFEHOME system (Pressman) Use case
name InitiateMonitoring Participating actors
homeowner, technicians, sensors Flow of events
(homeowner) --Homeowner wants to set the system
when the homeowner leaves house or remains in
house --Homeowner observes control
panel --Homeowner enters password --Homeowner
selects stay or away --Homeowner observes
that read alarm light has come on, indicating the
system is armed
18
Use detailed example (Pressman)--continued
Entry condition(s) Homeowner decides to set
control panel Exit condition(s) Control panel
is not ready homeowner must check all sensors
and reset them if necessary Control panel
indicates incorrect password (one beep)homeowner
enters correct password Password not
recognizedmust contact monitoring and response
subsystem to reprogram password Stay selected
control panel beeps twice and lights stay light
perimeter sensors are activated Away selected
control panel beeps three times and lights away
light all sensors are activated
19
Use casedetailed example (Pressman)

• Quality requirements
• Control panel may display additional text
  messages
• time the homeowner has to enter the password
  from the time the first key is pressed
• Ability to activate the system without the use
  of a password or with an abbreviated password
• Ability to deactivate the system before it
  actually activates

20
Use case additionssimplifications of use case
descriptions

• A. Include one use case includes another in its
  flow of events (cases A and B both include case
  C)
• Extend extend one use case to include
  additional behavior (cases D and E are extensions
  of case F)

ltltincludegtgt
A
C
B
ltltincludegtgt
ltltextendgtgt
D
F
E
ltltextendgtgt
21
Use case additions
C. Inheritance one use case specializes the
more general behavior of another G and H
specialize behavior of J)
G
J
Authenticate with password
authenticate
H
Authenticate with card
22
Use case continued
Examples what would be a use case for
vending machine user university student
management system (e.g., student changes
registration)
Use case name Participating actors Flow of
events Entry condition Exit condition Quality
requirements
23
System Tests

• Note
• Use cases can form a basis for system acceptance
  tests
• For each use case
• Develop one or more system tests to confirm that
  the use case requirements will be satisfied
• Add explicit test values as soon as possible
  during design phase
• These tests are now specifically tied to the use
  case and will be used as the top level acceptance
  tests
• Do not forget use cases / tests for performance
  and usability requirements (these may be
  qualitative as well as quantitative)

24
Additional useful uml constructs
25

• Question How do you start an OO design?
• --components?
• --objects?
• --how will they interact?
• Answer One common method is to start with
  components, along with any design patterns which
  can be identified.
• In general
• design is an iterative process
• all team members should take an active part in
  exploring possible designs
• simple designs are preferable to complex
  designs--but it may take several iterations to
  develop a simple design which meets the project
  requirements
• we will look at a subset of UML to do project
  design.

26
Analysis model (UML version) --functional model
(use cases and scenarios) --analysis object
model (static class and object
diagrams) --dynamic model (state and sequence
diagrams) As system is analyzed, specifications
are refined and made more explicit if necessary,
requirements are also updated
27
Example an activity diagram for analyzing a
system you are building
28
Review use case Graphical description
Text description Use case
name Participating actors Flow of events Entry
condition(s) Exit condition(s) Quality
requirements
Homeowner
Accesses system via internet
Sensors
System administrator
Reconfigures sensors and related system
features
Pressman, p. 163, Figure 7.3
29
Review Use case writing guide --each use
case should be traceable to requirements --name
should be a verb phrase to indicate user
goal --actor names should be noun
phrases --system boundary needs to be clearly
defined --use active voice in describing flow of
events, to make clear who does what --make sure
the flow of events describes a complete user
transaction ---if there is a dependence among
steps, this needs to be made clear --describe
exceptions separately --DO NOT describe the user
interface to the system, only functions --DO NOT
make the use case too longuse extends, includes
instead --as you develop use cases, develop
associated tests
30
Review Use case additionssimplifications of
use case descriptions

• A. Include one use case includes another in its
  flow of events (cases A and B both include case
  C)
• Extend extend one use case to include
  additional behavior (cases D and E are extensions
  of case F)

ltltincludegtgt
A
C
B
ltltincludegtgt
ltltextendgtgt
D
F
E
ltltextendgtgt
31
Review Use case additions
C. Inheritance one use case specializes the
more general behavior of another G and H
specialize behavior of J)
G
J
Authenticate with password
authenticate
H
Authenticate with card
32
Class and object diagrams Identify Objects from
Use Case Specifications USE ENDUSERs TERMS AS
MUCH AS POSSIBLE Entity objects things, for
example --nouns (customer, hospital,
infection) --real-world entities (resource,
dispatcher) --real-world activities to be tracked
(evacuation_plan) --data sources or sinks
(printer) Boundary objects system interfaces,
for example --controls (report(emergencybutton) -
-forms (savings_deposit_form) --messages
(notify_of_error) Control objects usually one
per use case --coordinate boundary and entity
objects in the use case Use the identified
objects in a sequence diagram to carry out the
use case
33
Common classes

• Other common types of classes which the developer
  can look for include
• tangible things, e.g., Mailbox, Document
• system interfaces and devices, e.g.,
  DisplayWindow, Input Reader
• agents, e.g., Paginator, which computes document
  page breaks, or InputReader
• events and transactions, e.g., MouseEvent,Customer
  Arrival
• users and roles, e.g., Administrator, User
• systems, e.g., mailsystem (overall),
  InitializationSystem (initializes)
• containers, e.g., Mailbox, Invoice, Event
• foundation classes, e.g., String, Date, Vector,
  etc.

34
Sequence Diagram
Sequence Diagram a sequence diagram also
models dynamic behavior typically a sequence
diagram shows how objects act together to
implement a single use case messages passed
between the objects are also shown sequence
diagrams help to show the overall flow of control
in the part of the program being modeled they
can also be used to show concurrent
processes asynchronous behavior
35
Sequence Diagram--Syntax
Objects in the sequence diagram are shown as
boxes at the top below each object is a dashed
vertical line--the objects lifeline an arrow
between two lifelines represents each
message arrows are labeled with message names
and can also include information on arguments and
control information two types of
control condition, e.g., is greaterthan
zero iteration, e.g., for all array
items return arrows can also be included
36
Sequence Diagram Example
37
ER diagrams

• Useful object relationships
• These diagrams represent the relationships
  between the classes in the system. These
  represent a static view of the system.
• There are three basic types of relationship
• inheritance ("is-a")
• aggregation ("has-a)
• association ("uses")
• These are commonly diagrammed as follows

38
ER diagram is-a
is-a draw an arrow from the derived to the base
class
39
ER diagram--has-a
has-a draw a line with a diamond on the end at
the "container" class. Cardinalities may also be
shown (11, 1n, 10m 1, i.e., any number gt
0, 11, i.e., any number gt 1)
tire car can exist independentlyshared
aggregation
person
arm is part of the person composition aggregation
arm
1 2
40
ER diagram--uses
uses or association there are many ways to
represent this relationship, e.g.,
employs
1
company
car
gasstation



n
employee
1
works for
41
CRC cards
CRC cards class--responsibilities--collaborators
cards "responsibilities" operators,
methods "collaborators" related classes (for
a particular operator or method)
Make one actual card for each discovered class,
with responsibilities and collaborators on the
front, data fields on the back. CRC cards are
not really part of UML, but are often used in
conjunction with it.
42
CRC card--example
Example (based on Horstmann, Practical
Object-Oriented Development in C and Java)
front back
Class Mailbox
Queue of new messages Queue of kept
messages Greeting Extension number Passcode
43
State Diagram
State Diagram another way of adding detail to
the design--models dynamic behavior describes
all the possible states a particular object can
be in and how that object's state changes as a
result of events that affect that object usually
drawn for a single class to show behavior of a
single object used to clarify dynamic behavior
within the system, as needed
44
State Diagram--Properties
A state diagram contains a "start" point, states,
and transitions from one state to another. Each
state is labeled by its name and by the
activities which occur when in that state.
Transitions can have three optional labels
Event Guard / Action. A transition is
triggered by an Event. If there is no Event,
then the transition is triggered as soon as the
state activities are completed. A Guard can be
true or false. If the Guard is false, the
transition is not taken. An Action is completed
during the transition.
45
State Diagram--Example
Example this state diagram example for an
"order" in an order-processing system is from
Fowler and Scott, UML Distilled (Addison-Wesley,
1997)
start
/get first item
not all items checked /get next item
all items checked all items available
Dispatching
Checking
initiate delivery
check item
all items checked some items not in stock
delivered
item received all items in stock
Delivered
Waiting
item received some items not in stock
46
Examplebank simulation (Horstmann)
Horstmann, Mastering Object-Oriented Design in
C, Wiley, 1995
Teller 1
Teller 2
Customer 1
Customer 3
Customer 2
Teller 3
Teller 4
47
Examplebank simulation (Horstmann), cont.
An initial solution (Horstmann, p. 388)
48
Examplebank simulation (Horstmann), cont.
An improved solution (Horstmann, p. 391)
49
Comparison
What simplifications have been made? Why?
50
Example How would we use the tools described so
far to design a smart vending machine? How
would we develop test cases at each stage? Use
cases? Class diagram? Sequence
diagram? Classes / CRC cards?