The Object-oriented Paradigm
and
The Unified Modeling Language (UML)
1
Problems of software development
"problems" of software development (review):
**conceptual integrity
**incremental build, progressive refinement
**large projects "differ" from small ones
programming paradigms (1950’s-present): attempts to deal
effectively with these problems, make software easier to
develop and to maintain
2
Languages and design methodology
Computer Language / Design Methodology: brief history:
1950's:unstructured, no information hiding--”spaghetti” code, GOTO, flowcharts
--machine code
--assembly lang.
--FORTRAN, LISP
(Algol; COBOL)
1980’s: structured, top-down design (“3 basic control structures, no GOTO”), modularity
--Pascal
--(C)
--Ada
1990’s: encapsulation, information-hiding, reuse, hardware/software codesign (from
simulation languages developed much earlier, e.g., Modula, simula)
--C++
--Java
2000’s: info hiding; web languages; environments encapsulating multiple languages, styles
--.NET, C#
--Python
3
--MATLAB, Mathematica, Labview, …
A Brief History: Computer Hardware, Computer Languages, Design Techniques
1950's:unstructured, no information hiding-”spaghetti” code, GOTO, flowcharts
--machine code
--assembly lang.
--FORTRAN, LISP (Algol; COBOL)
Early machines—large, central (Eniac)
wpclipart.com
chilton-computing.org.uk
1970s,1980s: structured, top-down design (“3 Supercomputers, “Minicomputers”, PCs,
multiuser machines, PICs
basic control structures, no GOTO”),
modularity
http://en.wikipedia.org/wiki/PIC
--Pascal, C, PL/I, Ada
_microcontroller#History
techxav.com
cse.mtu.edu
1990’s: encapsulation, information-hiding,
Beowulf clusters, Spread of the Internet
reuse, hardware/software codesign (from
simulation languages developed much earlier,
visual.merriame.g., Modula, simula)
webster.com
--C++, Java
2000’s: info hiding; web languages;
environments encapsulating multiple
languages, styles
--.NET, C#, Python, Perl, MATLAB,
Mathematica, Labview, …
“Ubiquitous computing”, laptops,.
Personal communication devices,
multicore processors, GPUs
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
A.
Useful OO techniques:
X
Ex: Object data
Y
Y
structures:
Z
Z
A. Base class
X
B.
W
B. Derived class
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
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in derived classes
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)
Overloading:
ex: cin >> num1;
>> 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 <class T>
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
[scenario: instance of use case; concrete informal
description of 1 feature; enhances understanding of use case]
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
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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 (e.g., CRC cards)
There exist many versions of UML—syntax may have slight
differences among versions—be aware of this as you read and
13
work on homework and projects
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
Text description
User Guide)
Place call
Cellular
network
Receive call
Use
scheduler
User
System boundary
Use case diagram—summarizes,
provides system overview
--Use case name
Place
(cellular network
place
conference
and receive calls)
call
--Participating actors
(cellular network and
human user)
--Flow of events
Receive
(network or user
additional
accesses network
to
call
use its functionality)
--Entry condition(s)
(user accesses
network using device
or password)
--Exit condition(s)
(call
completed
Validate
user
lost or network busy)
--Quality requirements
(speed, service quality)
--Open issues
(for future versions, e.g.)
Use Case
(Example)
Key:
Use Case
Actor
“Extends”
“Uses”
Text description—gives 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 case—detailed example (Pressman)
Example: “SAFEHOME” system (Pressman)
Use case: InitiateMonitoring
Arms/disarms
system
(Pressman text categories:
•Primary actor (1)
Homeowner
•Goal in context (2)
•Preconditions (3)
•Trigger (4)
•Scenario (5)
•Exceptions (6)
•Priority (system development) (7)
•When available (8)
System
administrator
•Frequency of use (9)
•Channel to actor (10)
•Secondary actors (11)
•Channels to secondary actors (12)
•Open issues (13) )
Accesses system
via internet
Sensors
Responds to
alarm event
Encounters an
error condition
Reconfigures
sensors
and related
system features
Pressman,
p. 163,
Figure 7.3
17
Use case—detailed 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
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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 recognized—must 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 case—detailed 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 additions—simplifications of use case descriptions
A. Include: one use case includes another in its flow of
events (cases A and B both include case C)
A
<<include>>
C
B
<<include>>
Example: report a fire: both “open incident” and “send fire
trucks” include the use case “view city map”
B. Extend: extend one use case to include additional
behavior (cases D and E are extensions of case F)
<<extend>>
D
F
E
<<extend>>
Example: ConnectionDown between two emergency
responders is a “special case” of Reportemergency but it
can use the basic functionality of ReportEmergency
21
Use case additions
C. Inheritance: one use case specializes the more general
behavior of another G and H specialize behavior of J)
Authenticate with
password
G
H
J
authenticate
Authenticate with card
Note: use case inheritance is BEHAVIORAL or
FUNCTIONAL inheritance
Standard OO inheritance is STRUCTURAL inheritance
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
TESTING at the system level:
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)
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Requirements  Specifications  …..
Use cases, tests
classes, …
Requirements must be:
--complete
--consistent
--unambiguous
--correct
25
Another way to organize requirements (text)--FURPS:
Functional requirements:
*F—functionality
Nonfunctional requirements:
“Quality”:
*U—Usability
*R—Reliability (Dependability—reliability, robustness, safety)
*P—Performance
*S—Supportability
“Constraints”:
*implementation requirements
Operations requirements, packaging requirements, legal requirements
* = important this quarter
26
Steps to turn requirements into specifications:
--identify actors
--identify scenarios (specific examples of use cases)
--identify use cases
--refine use cases as appropriate (extends / includes)—don’t overdo
this
--identify relationships among actors and use cases
--can now begin to identify objects needed ( design)
--also need to identify nonfunctional requirements
27
Use case writing guide (p. 137 of text):
--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 long—use extends, includes
instead
--as you develop use cases, develop associated tests
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Example—bank simulation (Horstmann)
Horstmann, Mastering ObjectOriented Design in C++, Wiley,
1995
Teller 1
Customer 3 Customer 2 Customer 1
Teller 2
Teller 3
Teller 4
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Use Cases--Bank
Goal: Develop a tool to simulate the bank to decide on optimal
values for number of tellers, number of customer queues, etc.
Use cases?
30
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Topics for week 3