ITIS312
Object Oriented Systems
Chapter 1
Introduction
Dr. Jihene Kaabi
óóó University Of Bahrain óóó
Second Semester 2019-2020
1
• Object-orientation is so called because this method sees
things that are part of the real world as objects.
ITIS312
Object Oriented Systems
What is Object-Orientation?
ü A phone is an object in the same way as a bicycle, a human being,
or an insurance policy are objects.
• In everyday life, we simplify objects in our thinking – we work
with models.
• Objects occurring in reality are reduced to a few features that
are relevant in the current situation.
Dr. Jihene Kaabi
óóó University Of Bahrain óóó
Second Semester 2019-2020
2
• Instead of real objects, we work with symbols.
ü example: in the figure below, we use model to describe a reality
ITIS312
Object Oriented Systems
What is Object-Orientation?
that a teacher owns a bicycle and he reads a book.
Dr. Jihene Kaabi
óóó University Of Bahrain óóó
Second Semester 2019-2020
3
• The characteristics required by an Object Oriented (OO)
approach include four aspects: identity, classification, inheritance,
ITIS312
Object Oriented Systems
What is Object-Orientation?
and polymorphism.
ØIdentity: data is quantized into discrete, distinguishable entities
called objects .
ü An object is a representation of a specific entity in the real world.
- Objects can be:
§ Concrete (or tangible), such as printer, computer, person, etc. or
§ Conceptual (or intangible), such as a job, course, etc.
- Two objects are distinct even if their attribute values (such as
name and size) are identical.
Dr. Jihene Kaabi
óóó University Of Bahrain óóó
Second Semester 2019-2020
4
ITIS312
Object Oriented Systems
Example: Object
Dr. Jihene Kaabi
óóó University Of Bahrain óóó
Second Semester 2019-2020
5
• Two aspects: information and behavior
Information :
1. has a unique identity.
ITIS312
Object Oriented Systems
Object Definition
2. has a description of its structure or the information that is
used to create it.
3. has a state representing its current condition, e.g. values of
some of its features.
Behavior:
1. what can the object do?
2. what can be done to it?
Dr. Jihene Kaabi
óóó University Of Bahrain óóó
Second Semester 2019-2020
6
Object Oriented Systems
Example: Object Definition
Information :
ITIS312
1. serial number.
2. model.
3. speed.
4. memory.
5. status.
Behavior:
1. print file.
2. stop printing.
3. remove file from queue.
Dr. Jihene Kaabi
óóó University Of Bahrain óóó
Second Semester 2019-2020
7
Ø Classification: objects with the same data structure (attributes)
and behavior (operations) are grouped into a class.
ITIS312
Object Oriented Systems
Object-Oriented Aspects
§ A class is an abstraction that describes properties important to an
application and ignores the rest.
ü Any choice of classes is arbitrary and depends on the application.
ü Each class describes a possibly infinite set of individual objects.
ü Each object is said to be an instance of its class.
ü An object has its own value for each attribute but shares the
attribute names and operations with other instances of the class.
ü An object contains an implicit reference to its own class.
Dr. Jihene Kaabi
óóó University Of Bahrain óóó
Second Semester 2019-2020
8
ITIS312
Object Oriented Systems
Classification: Example
Dr. Jihene Kaabi
óóó University Of Bahrain óóó
Second Semester 2019-2020
9
Ø Inheritance:
is
the
sharing
of
attributes
and
operations
(features) among classes based on a hierarchical relationship.
§ A superclass has general information that subclasses refine and
ITIS312
Object Oriented Systems
Object-Oriented Aspects
elaborate.
ü Each subclass inherits all the features of its superclass and adds
its own unique features.
ü ex. ScrollingWindow and FixedWindow are subclasses of Window.
- both subclasses inherit the features of Window.
- SrollingWindow adds a scroll bar and an offset.
The ability to factor out common features of several classes into a
superclass
can
greatly
reduce
repetition
within
designs
and
programs and is one of the main advantage of OO tehnology.
Dr. Jihene Kaabi
óóó University Of Bahrain óóó
Second Semester 2019-2020
10
Ø Polymorphism: the same operation may behave differently for
different classes.
§ An operation is a procedure or transformation that an object performs
ITIS312
Object Oriented Systems
Object-Oriented Aspects
or is subject to. Ex. RightJustify, display and move.
ü An implementation of an operation by a specific class is called a
method.
ü It may have more than one method implementing one operation,
each for a different class of object.
ü In an OO programming language, the language automatically
selects the correct method to implement an operation based on
the name of the operation and the class of the object being
operated on.
Dr. Jihene Kaabi
óóó University Of Bahrain óóó
Second Semester 2019-2020
11
Ø In this context development refers to the software life
cycle: analysis, design, and implementation.
ITIS312
Object Oriented Systems
What is OO Development?
Ø Object
Oriented
Methodology
(OOM)
is
a
system
development approach encouraging and facilitating re-use of
software components.
ØWith this methodology, a computer system can be developed
on a component basis which enables the effective re-use of
existing
components
and
facilitates
the
sharing
of
its
components by other systems.
Dr. Jihene Kaabi
óóó University Of Bahrain óóó
Second Semester 2019-2020
12
Ø
The process for OO development (software life cycle) consists of
building a model of an application and then adding details to it
during design. The methodology has the following stages.
ITIS312
Object Oriented Systems
OO Methodology
1. System conception: conceiving an application and formulating
tentative requirements.
2. Analysis: restate of the requirements from system conception
by
constructing
models
that
should
not
contain
any
implementation.
ü
The analyst must work with the requestor to understand the problem,
because problem statements are rarely complete or correct.
ü
The analysis model is a precise abstraction of what the desired system
must do, not how it will be done.
Dr. Jihene Kaabi
óóó University Of Bahrain óóó
Second Semester 2019-2020
13
Analysis: (cont’d)
ü
The analysis model has two parts:
1. The domain model: a description of the real-world objects reflected
within the system,
ITIS312
Object Oriented Systems
OO Methodology
2. The application model: a description of the parts of the application
system itself that are visible to the user.
3. System design:
ü
The overall architecture of the desired system is decided.
ü
While designing the system, the stress lies on the objects comprising the
system and not on the processes being carried out in the system.
Dr. Jihene Kaabi
óóó University Of Bahrain óóó
Second Semester 2019-2020
14
4. Class design:
ü
The class designer adds details to the analysis model in accordance with
the system design strategy.
ITIS312
Object Oriented Systems
OO Methodology
ü
The class designer elaborates both domain and application objects using
the same OO concepts and notation.
ü
The focus of class design is the data structures and algorithms needed to
implement each class.
5. Implementation:
ü
Implementers translate the classes and relationships developed during
class design into a particular programming language, database, or
hardware.
ü
Implementers should follow good software engineering practice so that
traceability to the design is apparent and so that the system remains
flexible and extensible.
Dr. Jihene Kaabi
óóó University Of Bahrain óóó
Second Semester 2019-2020
15
Ø
Three models are used to describe a system from different
viewpoints:
1.
The class model:
ü
ITIS312
Object Oriented Systems
Models for System Description
describes the static structure of the objects in a system and their
relationships.
ü
defines the context for software development—the universe of discourse.
ü
contains class diagrams (graphs whose nodes are classes and whose arcs
are relationships among classes).
2.
The state model:
ü
describes the aspects of an object that change over time.
ü
specifies and implements control with state diagrams (graphs whose
nodes are states and whose arcs are transitions between states caused by
events).
Dr. Jihene Kaabi
óóó University Of Bahrain óóó
Second Semester 2019-2020
16
3.
The interaction model:
ü describes how the objects in a system cooperate to achieve broader
results.
ITIS312
Object Oriented Systems
Models for system description
ü starts with use cases that are then elaborated with sequence and
activity diagrams.
ü a use case focuses on the functionality of a system (what a system
does for users).
ü a sequence diagram shows the objects that interact and the time
sequence of their interaction.
ü an activity diagram elaborates important processing steps.
The three models are separate parts of the description of a complete
system but are cross-linked.
Dr. Jihene Kaabi
óóó University Of Bahrain óóó
Second Semester 2019-2020
17
Ø Several themes pervade OO technology and are well supported.
ü Abstraction: is the presentation of simple concept (or object)
to the external world.
§ Abstraction concept is to describe a set of similar concrete
ITIS312
Object Oriented Systems
OO Themes
entities.
§ It focuses on the essential, inherent aspects of an entity
and ignoring its accidental properties.
§ The abstraction concept is usually used during analysis:
deciding only with application-domain concepts, not making
design and implementation decisions.
The ability to abstract is the most important skill required for OO
development.
Dr. Jihene Kaabi
óóó University Of Bahrain óóó
Second Semester 2019-2020
18
ü Encapsulation (information hiding): means as much as shielding.
ü Each object-oriented object has a shield around it.
ITIS312
Object Oriented Systems
OO Themes
ü Objects can't 'see' each other. They can exchange things
though, as if they are interconnected through a hatch.
ü The object encapsulates both data and the logical procedures
required to manipulate the data.
Dr. Jihene Kaabi
óóó University Of Bahrain óóó
Second Semester 2019-2020
19
ü Encapsulation: Example
Ø Encapsulation separates implementation from users or clients.
ITIS312
Object Oriented Systems
OO Themes
Dr. Jihene Kaabi
Ø Client depends on interface.
óóó University Of Bahrain óóó
Second Semester 2019-2020
20
ü Sharing: inheritance of both data structure and behavior lets
subclasses share common code.
This sharing via inheritance is one of the main advantages of OO
ITIS312
Object Oriented Systems
OO Themes
development.
ü Emphasis on the essence of an object: OO development places a
greater emphasis on data structure and a lesser emphasis on procedure
structure than functional-decomposition methodologies.
Dr. Jihene Kaabi
óóó University Of Bahrain óóó
Second Semester 2019-2020
21