Transcript Distributed Programming

Object Oriented Software Development
CIS 50-3

Marc Conrad



D104 (Park Square Building)
[email protected]
Today:
Object Oriented Analysis
The most single important ability in object
oriented analysis and design is to skillfully assign
responsibilities to software components.
16/07/2015 23:24:13
Marc Conrad - University of Luton
1
What is an Object?





An object is an entity which consists of a number of
operations and a state which remembers the effect of
the operations.
State is regarded as information which is saved in a
set of variables.
Operations (aka. methods) read and/or affect the
information.
The only part that can be seen by an outsider are the
operations. For this reason, operations are also
known as behaviours.
Information is hidden to the outsider.
16/07/2015 23:24:13
Marc Conrad - University of Luton
2
90
80
70
60
East
West
North
50
40
30
What is an object?





20
10
0
1st Qtr 2nd Qtr 3rd Qtr 4th Qtr
Tangible Things as a car, printer, ...
Roles
as employee, boss, ...
Incidents
as flight, overflow, ...
Interactions
as contract, sale, ...
Specifications
as colour, shape, …
 An object represents an individual, identifiable
item, unit, or entity, either real or abstract,
with a well-defined role in the problem
domain.
 An "object" is anything to which a concept
applies.
16/07/2015 23:24:13
Marc Conrad - University of Luton
3
Example:
A Person as an Object
Information:
Name,
Age,
Address,
Friends,
...
16/07/2015 23:24:13
Behaviour:
jump
bend legs
stretch legs
lift arms,
...
walk
talk
Marc Conrad - University of Luton
4
UML diagram of the
Person class
Person
-name: string
-yearOfBirth: int
+create(theName: string ,theYear: int)
+jump()
+getAge(this year: int):int
Name
Private data
(attributes)
Initialisation
(constructor)
Public
behaviour
(methods)
Java code of the Person class
public class Person {
Name
private String name;
private int yearOfBirth;
Private data
(attributes)
public Person(String theName, int theYear) {
name = theName;
yearOfBirth = theYear;
}
public void jump() {
System.out.println(name + " jumps");
}
public int getAge(int thisYear) {
return thisYear - yearOfBirth;
}
}
Initialisation
(constructor)
Public
behaviour
(methods)
C++ code of the Person class
#include <iostream>
class Person{
private:
char name[20];
int yearOfBirth;
public:
Person(char *theName, int theYear) {
yearOfBirth = theYear;
sprintf(name, theName);
}
void jump() {
std::cout << name <<
" jumps" << std::endl;
}
int getAge(int thisYear) {
return thisYear - yearOfBirth;
}
};
Name
Private data
(attributes)
Initialisation
(constructor)
Public
behaviour
(methods)
Basic Terminology:
Classes and Instances




A Class is a template or abstract description of the
same type of objects. It defines the common features
of the objects, that is the operations and information
structure.
An Instance is an object created from a class.
An instance’s behaviour and information structure is
defined in the class.
Its current state (values of instance variables) is
determined by operations performed on it.
16/07/2015 23:24:13
Marc Conrad - University of Luton
8
Basic Terminology:
Inheritance

http://www.cs.nmsu.edu/~rth/cs/cs177/map/inheritd.html:


http://www.parashift.com/c++-faq-lite/basics-of-inheritance.html:


Inheritance is a way of relating two classes so that
one class may use another class's members
without redefining them.
Inheritance is what separates abstract data type
(ADT) programming from OO programming.
The basic principle is simple:
 A class gets the state and behaviour of
another class and adds additional state and
behaviour.
16/07/2015 23:24:13
Marc Conrad - University of Luton
9
What is the purpose of Inheritance?



Specialisation:
 Extending the functionality of an existing
class.
Generalisation:
 Sharing commonality between two or more
classes.
Polymorphism.
 Implementation of different behaviour to
the same message (depending on the type
of the object).
16/07/2015 23:24:13
Marc Conrad - University of Luton
10
Inheritance - related Terminology




Derived class or subclass or child class.
 A class which inherits some of its attributes and
methods from another class.
Base class or superclass or parent class.
 A class from which another class inherits.
Ancestor.
 A class’s ancestors are those from which its own
superclasses inherit.
Descendant.
 A class’s descendants are those which inherit from
its subclasses.
16/07/2015 23:24:13
Marc Conrad - University of Luton
11
Inheritance vs. Aggregation

Inheritance means that one class inherits the
characteristics of another class.
This is also called a “is a” relationship:
A car is a vehicle

A student is a person
Aggregation describes a “has a” relationship.
One object is a part of another object.
A car has wheels
16/07/2015 23:24:13
A person has legs
Marc Conrad - University of Luton
12
Basic Terminology:
Polymorphism





Original meaning: “Having many forms”
The sender of a stimulus doesn’t need to know the
receiver’s class.
Different receivers can interpret the message in
their own way.
Consequence: different receivers can response to
the same stimulus based on their interpretation.
So we can have a variety of objects who process
the same piece of data in different ways.
Implemented via method overloading and
overriding.
16/07/2015 23:24:13
Marc Conrad - University of Luton
13
Basic Terminology:
Encapsulation






Encapsulation is the process of hiding the
implementation details of an object.
The only access to manipulate the object data is
through its interface.
It protects an object’s internal state from being
corrupted by other objects.
Also, other objects are protected from changes in the
object implementation.
Encapsulation allows objects to be viewed as ‘black
boxes’.
Communication is achieved through an ‘interface’.
16/07/2015 23:24:13
Marc Conrad - University of Luton
14
Example: Encapsulation


Encapsulation is the practice of including in an
object everything it needs hidden from other
objects. The internal state is usually not accessible
by other objects.
But see also:

http://www.parashift.com/c++-faq-lite/classes-and-objects.html#faq-7.6
Public:
Has an age and
can jump.
16/07/2015 23:24:13
Private:
Has a name and a year
of birth.
Marc Conrad - University of Luton
15
The Analysis Phase




In software engineering, analysis is the process of
converting the user requirements to system
specification (system means the software to be
developed).
System specification, also known as the logic structure,
is the developer’s view of the system.
Function-oriented analysis – concentrating on the
decomposition of complex functions to simply ones.
Object-oriented analysis – identifying objects and the
relationship between objects.
16/07/2015 23:24:13
Marc Conrad - University of Luton
16
Object Oriented Analysis





Identifying objects: Using concepts, CRC cards,
stereotypes, etc.
Organising the objects: classifying the objects
identified, so similar objects can later be defined in
the same class.
Identifying relationships between objects: this helps
to determine inputs and outputs of an object.
Defining operations of the objects: the way of
processing data within an object.
Defining objects internally: information held within
the objects.
16/07/2015 23:24:13
Marc Conrad - University of Luton
17
Three ways to do Object Oriented
Analysis (there are more…).




Conceptual model (Larman)
 Produce a “light” class diagram.
CRC cards (Beck, Cunningham)
 Index cards and role playing.
Analysis model with stereotypes (Jacobson)
 Boundaries, entities, control.
A good analyst knows more than one strategy and
even may mix strategies in order to identify the
objects and relationships for the design phase.
16/07/2015 23:24:13
Marc Conrad - University of Luton
18
Conceptual Model - Overview



A conceptual model is a representation of
concepts in a problem domain.
In UML it is basically a “class diagram without
operations”.
It may show:
 Concepts
 Associations of concepts
 Attributes of concepts
16/07/2015 23:24:13
Marc Conrad - University of Luton
19
The conceptual model:
Strategies to Identify Concepts



Finding Concepts with the
Concept Category List.
Finding Concepts with
Noun Phrase Identification.
A central distinction between object oriented and
structures analysis: division by concepts (objects)
rather than division by functions.
16/07/2015 23:24:13
Marc Conrad - University of Luton
20
The Concept Category List







physical or tangible
objects
specifications, designs,
descriptions of things
places
transactions
transaction line items
roles of people
containers of other
things
16/07/2015 23:24:13










things in a container
abstract noun concepts
organisations
events
processes
rules and policies
catalogues
records
services
manuals, books
Marc Conrad - University of Luton
21
Finding Concepts with
Noun Phrase Identification


Identify the noun and noun phrases in textual
descriptions of a problem domain and
consider them as candidate concepts or
attributes.
Care must be applied with this method. A
mechanical noun-to-concept mapping isn’t
possible, and words in natural languages are
ambiguous (especially English).
16/07/2015 23:24:13
Marc Conrad - University of Luton
22
The “return item” Use case.
Exercise: Find the Nouns!



The system controls a recycling machine for
returnable bottles, cans and crates. The machine
can be used by several customers at the same time
and each customer can return all three types of
item on the same occasion. The system has to
check, for each item, what type has been returned.
The system will register how many items each
customer returns and when the customer asks for a
receipt, the system will print out what was
deposited , the value of the returned items and the
total return sum that will be paid to the customer.
An operator also … (not in “return item” Use Case)
16/07/2015 23:24:13
Marc Conrad - University of Luton
23
Case Study: Nouns in
The Recycling machine The “return item” Use case.



The system controls a recycling machine for
returnable bottles, cans and crates. The machine
can be used by several customers at the same time
and each customer can return all three types of
item on the same occasion. The system has to
check, for each item, what type has been returned.
The system will register how many items each
customer returns and when the customer asks for a
receipt, the system will print out what was
deposited , the value of the returned items and the
total return sum that will be paid to the customer.
An operator also … (not in “return item” Use Case)
16/07/2015 23:24:13
Marc Conrad - University of Luton
24
Case Study:
Nouns found in the description:








recycling machine
bottles, cans, and crates
machine
customers, customer
types of item, item, type, returned items
system
receipt
return sum
16/07/2015 23:24:13
Marc Conrad - University of Luton
25
Case Study:
Discussion of “recycling machine”.








recycling machine
bottles, cans and crates
machine
 This concept is the “overall system”. As
customers, customer
we consider only one single use case, it
types of item, item, type,
is better to name this concept in the
returned items
context of this use case, e.g.
system
receipt  Deposit item receiver
return sum
16/07/2015 23:24:13
Marc Conrad - University of Luton
26
Case Study:
Discussion of “bottles, cans, and crates”.








deposit item receiver
bottles, cans, and crates
machine
 In a conceptual model it is usually better
customers, customer
to use singular and multiplicities instead
types of item, item, type
plural.
returned of
items
system As bottle, can and crate have much in
receipt common (they are processed as items),
they could be generalised to an “item”.
return sum
We should remember this for later
(inheritance).
16/07/2015 23:24:13
Marc Conrad - University of Luton
27
Case Study:
Discussion of “machine” and “system”.








deposit item receiver
bottle, can, crate
machine
 “Machine” and “System”
customers, customer mean here the same,
namely the “Recycling
types of item, item, type,
returned items
machine”, i.e. the
system
 Deposit item receiver
receipt
return sum
16/07/2015 23:24:13
Marc Conrad - University of Luton
28
Case Study:
Discussion of “customers” and “customer”.


deposit item receiver
bottle, can, crate




customers, customer
types of item, item, type, 
returned items




receipt
return sum
16/07/2015 23:24:13
The customer has already
been identified as an actor.
They are outside of the
system.
We establish a concept, that
interfaces with the customer
(and is inside the system):
 Customer panel
Marc Conrad - University of Luton
29
Case Study:
Discussion of “item” (etc.).


deposit item receiver
bottle, can, crate

customer panel
types of item, item, type,
returned items







receipt
return sum
16/07/2015 23:24:13

The items that are
inserted in the
machine.
Good candidate as
superclass for bottle,
can, crate.
Let’s call it
 Deposit item
Marc Conrad - University of Luton
30
Case Study:
Discussion of “receipt”.


deposit item receiver
bottle, can, crate




customer panel
deposit item



receipt
return sum
16/07/2015 23:24:13

The concept that
“remembers” all items
inserted in the
machine.
To distinguish it from
the piece of paper
returned to the
customer, call it
 Receipt basis
Marc Conrad - University of Luton
31
Case Study:
Discussion of “return sum”.


deposit item receiver
bottle, can, crate




customer panel
deposit item




receipt basis
return sum
16/07/2015 23:24:13
The sum that it is returned
to the customer is actually
computed by adding up all
values of the items stored in
the receipt basis.
The sum itself is only a
primitive data value, and
may therefore not be
considered as a concept.
Marc Conrad - University of Luton
32
Case Study:
Discussion of other concepts.


deposit item receiver
bottle, can, crate




customer panel
deposit item


receipt basis

16/07/2015 23:24:13


These are the concepts
identified by nouns. Did we
forget something?
Check the
“Concept Category List” !
The system “interfaces” with
the physical object “printer”,
so we add an interface
concept
 Receipt printer
Marc Conrad - University of Luton
33
Case Study:
Summary of concepts identified in the analysis


deposit item receiver
bottle, can, crate

So far we have
identified:




customer panel
deposit item



receipt basis



Concepts
A generalisation
relationship.
Next step: Finding
associations.
receipt printer
16/07/2015 23:24:13
Marc Conrad - University of Luton
34
How to make a conceptual
model.




Find the concepts
Draw them in a conceptual model
Add associations
Add attributes
16/07/2015 23:24:13
Marc Conrad - University of Luton
35
Drawing of Concepts
Customer panel
Deposit item receiver
Deposit item
Receipt printer
Receipt basis
Can
16/07/2015 23:24:13
Bottle
Crate
Marc Conrad - University of Luton
36
Adding Associations


If one concept needs to know of a
another concept for some duration
they should be linked by an
association.
Also use the following list in order
to identify associations.
16/07/2015 23:24:13
Marc Conrad - University of Luton
37
Common Association List







A is a part of B
A is contained in B
A is a description for B
A is a line item of a
transaction or report B
A is known or reported
in B
A is a member of B
A is a organisational
subunit of B
16/07/2015 23:24:13






A uses or manages B
A communicates with B
A is related to a
transaction B
A is a transaction
related to another
transaction B
A is next to B
A is owned by B
Marc Conrad - University of Luton
38

Adding associations

The Customer panel
communicates to the receiver
when an item is inserted.
Also when the receipt is
requested.
Customer panel
initiates action
Deposit item receiver
Deposit item
Receipt printer
Receipt basis
Can
16/07/2015 23:24:13
Bottle
Crate
Marc Conrad - University of Luton
39

Adding associations
Customer panel

The Deposit item receiver
manages Deposit items:
The items are classified.
initiates action
Deposit item receiver
classifies
Deposit item
Receipt printer
Receipt basis
Can
16/07/2015 23:24:13
Bottle
Crate
Marc Conrad - University of Luton
40

Adding associations


Customer panel
The Deposit item receiver
communicates to Receipt basis:
Items received and classified are
stored.
It also creates the receipt basis when
it is needed for the first time.
initiates action
Deposit item receiver
classifies
creates & notifies
Deposit item
Receipt printer
Receipt basis
Can
16/07/2015 23:24:13
Bottle
Crate
Marc Conrad - University of Luton
41

Adding associations
The Receipt basis collects
Deposit items.
initiates action
Customer panel
Deposit item receiver
classifies
creates & notifies
captures
Deposit item
Receipt printer
Receipt basis
Can
16/07/2015 23:24:13
Bottle
Crate
Marc Conrad - University of Luton
42

Adding associations
On request by the Customer
Panel the Deposit item receiver
initiates printing of a receipt
on the printer.
initiates action
Customer panel
Deposit item receiver
classifies
creates & notifies
captures
prints on
Deposit item
Receipt printer
Receipt basis
Can
16/07/2015 23:24:13
Bottle
Crate
Marc Conrad - University of Luton
43


Adding associations

Customer panel
Adding multiplicities
Only one association here is a
1 to many relationship
All others are 1 to 1.
initiates action
classifies
creates & notifies
Receipt basis
Deposit item receiver
prints on
captures
Deposit item
1..*
Can
16/07/2015 23:24:13
Bottle
Receipt printer
Crate
Marc Conrad - University of Luton
44
Adding Attributes



An attribute is a logical data value of an object.
Attributes in a conceptual model are simple data
values as
 Boolean, Date, Number, String (Text), Time,
Address, Colour, Price, Phone Numbers, Product
Codes, etc.
Sometimes it is difficult to distinguish between
attributed and concepts
 E.g. Concept “Car” vs. attribute “Reg. Number”.
16/07/2015 23:24:13
Marc Conrad - University of Luton
45

Adding attributes
Customer panel

The Deposit item has a value.
Also it will be assigned a
number that shows later on the
receipt.
initiates action
classifies
creates & notifies
Receipt basis
Deposit item receiver
prints on
captures
Deposit item
1..*
number
value
Can
16/07/2015 23:24:13
Bottle
Receipt printer
Crate
Marc Conrad - University of Luton
46
In order to be classified by the Deposit
item receiver each item has also a weight
and a size.
However this is the same for each type of
item, but different between the types.

Adding attributes
Customer panel

initiates action
classifies
creates & notifies
Receipt basis
Deposit item receiver
prints on
captures
Deposit item
1..*
Can
weight
size
16/07/2015 23:24:13
number
value
Bottle
weight
size
Receipt printer
Crate
weight
size
Marc Conrad - University of Luton
47
NOT in a conceptual model:
 arrows
 dotted lines
 methods, operations, functions

Summary
Customer panel
initiates action
classifies
creates & notifies
Receipt basis
Deposit item receiver
prints on
captures
Deposit item
1..*
Can
weight
size
16/07/2015 23:24:13
number
value
Bottle
weight
size
Receipt printer
Crate
weight
size
Marc Conrad - University of Luton
48
CRC cards & Role playing


Not part of the UML design process but useful
in detecting responsibilities of objects are
CRC cards (developed by Kent Beck and Ward
Cunningham).
CRC stands for Class-ResponsibilityCollaborator. They look like:
Name
Responsibilities
Collaborators
16/07/2015 23:24:13
Marc Conrad - University of Luton
49
CRC cards & Role playing



CRC cards are index cards, one for each
class, upon which the responsibilities and
collaborators of a class are written.
They are developed in a small group session
where people role play being the various
classes.
Each person holds onto the CRC cards for the
classes that they are playing the role of.
http://www.csc.calpoly.edu/~dbutler/tutorials/winter96/crc_b/
16/07/2015 23:24:13
Marc Conrad - University of Luton
50
Example: Recycling machine
CRC cards
Customer panel

Deposit item
receiver


Dep. item receiver

Printer
Deposit Item
Receipt Basis





receive items
receive print
request
classify items
create Receipt
Basis
print receipt
Etc.
16/07/2015 23:24:13
Marc Conrad - University of Luton
51
The Object Oriented Analysis
Model (Jacobson)




An analysis model is used to represent the system
specification.
To achieve robustness and stability the model must
be implementation environment independent.
Any change in the implementation environment will
not affect the logical structure of the system.
The model must be able to capture information,
behaviour (operations) and presentation (inputs and
outputs).
16/07/2015 23:24:13
Marc Conrad - University of Luton
52
Behaviour - Information Presentation

The model is defined in information - behaviour presentation space.
behaviour
information
presentation
16/07/2015 23:24:13
Marc Conrad - University of Luton
53
Syntax
of the Object Oriented Analysis Model

Within an use case, we employ three types of
objects (in Rational Rose, they are known as three
types of entities or stereotypes):
Entity
On information – behaviour plane
and incline to information axis
Boundary / Interface
Control
16/07/2015 23:24:13
On the presentation axis
On information – behaviour
plane but incline towards
behaviour axis
Marc Conrad - University of Luton
54
Entity, Control, Interface
behaviour
information
presentation
16/07/2015 23:24:13
Marc Conrad - University of Luton
55
Semantics
of the Object Oriented Analysis Model



An entity object models information that shows
the state of a system. This information is often
used to record the effects of operations and
therefore is related to the behaviours of the
system.
A boundary/interface object models inputs and
outputs and operations that process them.
A control object models functionality/operations
regarding to validate and decide whether to
process and pass information from the interface
object to the entity object or the way around.
16/07/2015 23:24:13
Marc Conrad - University of Luton
56
Pragmatics
of the Object Oriented Analysis Model

Identifying interface objects


Identifying entity objects


functions directly related to actors.
information used in an use case and functions
of processing the information.
Identifying control objects

functions that link interface objects and entity
objects
16/07/2015 23:24:13
Marc Conrad - University of Luton
57
Example:
The Recycling machine

Identifying interface objects


Identifying entity objects




Printer, Customer Panel
Long term information: Crate, Bottle, Can
Superclass: Deposit item
Short term information: Receipt basis
Identifying control objects

Deposit item receiver
16/07/2015 23:24:13
Marc Conrad - University of Luton
58
The Recycling machine
Interface Objects
Customer panel
16/07/2015 23:24:13
Receipt printer
Marc Conrad - University of Luton
59
The Recycling machine
Entity Objects
Receipt basis
Deposit items
Can
16/07/2015 23:24:13
Bottle
Marc Conrad - University of Luton
Crate
60
The Recycling machine
Link Interface and Entity Objects by a
Control Object
Deposit item receiver
Customer panel
Receipt printer
Receipt basis
Deposit items
Can
16/07/2015 23:24:13
Bottle
Marc Conrad - University of Luton
Crate
61
Summary Object Oriented Analysis



The main task is identifying the objects.
Also: Relationships between objects.
Three strategies:

Conceptual Model (concepts as objects)

CRC cards (index cards as objects)

Analysis Model (Stereotypes as objects)
Next step: Design.
16/07/2015 23:24:13
Marc Conrad - University of Luton
62