Introduction

IntroductionIntroduction

Preeti MishraCourse Instructor

Motivation

• You got a gun

• You were the proud owner of the nice gun!

• You used it:

• You claimed you know how to use a gun!

Motivation

• You learnt Java…• You know the syntax and semantics.• You have written small programs that work.• You claimed you know object-oriented software

development!!• This syndrome is not restricted to students

alone…

Our Project Manager For the Rest of the Course!

Hopelessly incompetent at management. He does not understand technical issues but always tries to disguise this, usually by using buzzwords that he does not understand himself. Often lacks Ethics…

Object

• Any real world entity: chair, fan, student, cow• Object has crisp boundaries• You can physically or logically perceive an object • Object has:

• State ( values of attributes)• Behavior( method response)• Identity( address+name)

Taking about the dog

Attributes(these will be common to all dogs)

State( talking about dog obove)

Breed Labrador

Owner Mr. crazy

Batch_no 420_IM

Vaccinated No

Hobbies Music

badhabbits smoking

• Behavior: • gets_vaccination• Runs• Listensongs….

• Identity: • Batch_no ( it is unique for all dogs)

Task:

• Think of an object• Give its state- now deduce the

attributes from this state• Talk of the identity

Modeling

• "Modelling" is describing something you know. A good model makes correct assertions. (problem domain)

• "Designing" is manipulating space for things you don't know. A good design e.g., lets you change things easily (there are many dimensions of 'goodness').( moving towards solution domain)

Putting it together

• Object Oriented Modeling and Design

Outcomes of the course

• To gain enough competence in OOAD to tackle a complete OO project

• It gives a thought to talk about a common language talking about requirements , design and interfaces

• Address main principles of OO design and what major tasks are appropriate for developing OO models and software, the issues and options in reuse and component based development

AbstractionAbstraction

Object Oriented Concepts:

What we learned

• People tend to see the same thing in different manner

• Why So??– Due to various perspectives, interests

• Technically we will refer this syndrome as Abstraction

What is..

• An abstraction focuses on the outside view of an object andseparates an object’s behaviour from its implementation

• a simplified description, or specification, of a system that emphasizes some of the system's details or properties while suppressing others. A good abstraction is one that emphasizes details that are significant to the reader or user and suppresses details that are, at least for the moment, immaterial or diversionary“

• Nearly all programming languages designed since 1980 support data abstraction

Thus

• “An abstraction denotes the essential characteristics of an object that distinguish it from all other kinds of objects and thus provide crisply defined conceptual boundaries,

relative to the perspective of the viewer”-Grady Booch

Realized in programming by..

• Abstract data types/ classes• Abstract keyword• Class…

EncapsulationEncapsulation

Need??

• Large programs have two special needs:– Some means of organization, other

than simply division into subprograms

– Some means of partial compilation (compilation units that are smaller than the whole program)

Hence encapsulation

• “Encapsulation is a mechanism used to hide the data, internal structure, and implementation details of an object.

• All interaction with the object is through a public interface of operations.”

• Abstraction and encapsulation are complementary concepts: abstraction focuses upon the observable behaviour of an object, whereas encapsulation focuses upon the implementation that gives rise to this behaviour.

• For abstraction to work, implementations must be encapsulated"

Defined as..

• “Encapsulation is the process of compartmentalizing the elements of an abstraction that constitute its structure and behaviour; encapsulation serves to separate the contractual interface of an abstraction and its implementation.”

– Grady Booch

Encapsulation is achieved through

• Encapsulation is most often achieved through information hiding, which is the process of hiding all the secrets of anobject that do not contribute to its essential characteristics; typically, the structure of an object is hidden, as well as the ,implementation of its methods.

In programming

• Encapsulation Abstraction= Class • For eg: think of a person as student• From this perspective think of his

description/properties• Now compartmentalize these properties into:

– attributes + behavior– Make attributes as : member variables/ data members– Make behavior: member functions/ methods– Name the entity as some noun : Student (because its

meaningful according to the perspective)

And we have..

Class Student{int roll_no, marks;String Name, branch, year;int get_Attendence()int check_percentage()}

ModularityModularity

Thus

• The act of partitioning a program into individual components can reduce its complexity to some degree. .

• Although partitioning a program is helpful for this reason, a more powerful justification for partitioning a program is that it creates a number of well defined, documented boundaries within the program.

• modularization consists of dividing a program into modules which can be compiled separately, but which have connections with other modules.

• The overall goal of the decomposition into modules is the reduction of software cost by allowing modules to be designed and revised independently. .

Defined as..

• Modularity is the property of a system that has been decomposed into a set of cohesive and loosely coupled modules

HeirarcyHeirarcy

What is the need

• A set of abstractions often forms a hierarchy, and by identifying these hierarchies in our ,design, we greatly simplify our understanding of the problem

Defined as..

• Hierarchy is a ranking or ordering of abstractions.

• Is-a relation• Kind-of

PolymorphismPolymorphism

We learned

• Generally, the ability to appear in many forms.• The same invocation can produce “many

forms” of results• The same method name and signature can

cause different actions to occur, – depending on the type of object on which

the method is invoked• Promotes extensibility• New objects types can respond to existing

method calls

• Polymorphism exists when the features of inheritance and dynamic binding interact. It is

perhaps the most powerful feature of object-oriented programming languages

Defined as..

• In object-oriented programming, polymorphism refers to a programming language's ability to process objects differently depending on their data type or class. More specifically, it is the ability to redefine methods for derived classes.

Concurrency, Persistancy, Typing

Concurrency, Persistancy, Typing

Typing

• "A type is a precise characterization of structural or behavioural properties which a collection of entities all share“

• Concept of Typing and class are similar but• Typing is the enforcement Of the class of an object,

such, that objects of different types may not be interchanged, or at the most, they may be interchanged only in very restricted ways.

An OO-Programming language can be:

• Strongly typed(violation of type conformance can be detected at the time of compilation)

• Weakly typed(have tendencies toward strong typing, but it is possible to ignore or suppress the typing rules.)

• Untyped (Violations of type conformance may not be known until execution, and usually manifest themselves as execution errors)

Typing in

• Static and Dynamic Binding• Support polymorphic behavior

Concurrency

• For certain kinds of problems, an automated system may have to handle many different events simultaneously.

• Other problems may involve so much computation that they exceed the capacity of any single processor.

• In each of these cases, it is natural to consider using a distributed set of computers for the target implementation or to use processors capable of multitasking.

Thus ..

• concurrency focuses upon process abstraction and synchronization

• The object is a concept that unifies these two different viewpoints:

• each object may represent a separate thread of control (a process abstraction). Such objects are called active. In a system based on an object-oriented design,

• we can conceptualize the world as consisting of a set of cooperative objects, some of which are active and thus serve as centres of independent activity.

Persistency

• objects in a database outlive the execution of a single program.

• This spectrum of object persistence encompasses the following:– “Transient results in expression evaluation– Local variables in procedure activations– Own variables [as in ALGOL 60], global variables, and heap

items whose extent is– different from their scope– Data that exists between executions of a program– Data that exists between various versions of a program– Data that outlives the program"

Contd..

• introducing the concept of persistence to the object model gives rise to object-oriented databases

• In practice, such databases build upon proven technology, such as – sequential, – indexed, – hierarchical, – network, or – relational database

Defined as..

• Persistence is the property of an object through which its existence transcends time (i.e. the object continues to exist after its creator ceases to exist) and/or space (i. e. the objects location moves from the address space in which it was created).

OOD

Object-oriented design is a method of– design encompassing the process of object-

oriented decomposition and – a notation for depicting both

• logical and • physical as well as • static and • dynamic models

of the system under design.

ObjectObject•State•Behavior/ operations•Identity•Roles-responsibility•Life span

What is an Object?

• From the perspective of human cognition, an object is any of the following:– A tangible and/or visible

thing– Something that may be

apprehended intellectually– Something toward which

thought or action is directed– something that exists in time

and space.

Defined as

• An object has state, behaviour, and identity; the structure and behaviour of similar objects are defined in their common class; the terms instance and object are interchangeable.

Object: State

Property(attribute)

Current value(State)

Amount of money $45

No to slots 20

No of empty slots 5

No of filled slots 10

Price per slot …

State: defined as

• The state of an object encompasses all of the (usually static) properties of the object plus the current (usually dynamic) values of each of these properties.

Behavior

• the behaviour of an object represents its outwardly visible and testable activity

• behaviour also notes that the state of an object affects its behaviour as well.

Behavior : defined as

• Behaviour is how an object acts and reacts, in terms of its state changes and message passing.

• Thus:– The state of an object represents the cumulative

results of its behaviour

Operations: means to show behaviour

(Operation/methods/memberfunctions)

• An operation denotes a service that a class offers to its clients. • In practice, we have found that a client typically performs five

kinds of operations upon an object:– Modifier :An operation that alters the state of an object– Selector :An operation that accesses the state of an object, but does

not alter the state– Iterator :An operation that permits all parts of an object to be accessed

in some well-defined order– Constructor: An operation that creates an object and/or initializes its

state– Destructor An operation that frees the state of an object and/or

destroys the object itself

Task to do

• For a Stack data structure identify :

• State: properties and current values

• Behavior• Operations of different

categories

Identity

New terms??

• Copying, Assignment, and Equality• What’s the difference???

Identity: defined as

• “Identity is that property of an object which distinguishes it from all other objects "

Roles and Responsibilities

• all of the methods and free subprograms associated with a particular object comprise its protocol.

Roles

• object's allowable behavior, and so comprises the entire static and dynamic view of the object.

• For most nontrivial abstractions, it is useful to divide this larger protocol into logical groupings of behavior.

• These collections, which thus partition the behavior space• of an object, denote the roles that an object can play. • a role is a mask that an object wears , and so defines a

contract between an abstraction and its clients

Responsibility

• The responsibilities of an object to "include two key items: – the knowledge an object maintains and – the actions an object can perform.

• Responsibilities are meant to convey a sense of the purpose of an object and its place in the system.

• The responsibilities of an object are all the services it provides for all of the contracts it supports"

Object : Life Span

• Object Life Span :The lifetime of an object extends from the time it is first created (and thus first consumes space) until that space is reclaimed .

• To explicitly create an object, we must either declare it or allocate it.

• Object destruction may vary …• Persistent objects have slightly different semantics

regarding destruction

•Object Oriented Methodologies Uniform Approach Modeling•Object Oriented Methodologies Uniform Approach Modeling

Object Oriented Development

• Object-Oriented development requires that object-oriented techniques be used during – the analysis, and – implementation of the system.

• An object-oriented approach to the development of software was proposed in late 1960s.

Object Modeling Technique

Object Modeling Technique

What is modeling??

• A model is an abstraction of something for the purpose of understanding it before building it.

• Because, real systems are generally very complex. In order to understand the real system, we have to simplify the system.

• So a model is an abstraction that hides the non-essential characteristics of a system and highlights those characteristics, which are pertinent to understand it.• Model is a simplified representation of reality.

What is modeling??

• Most modeling techniques used for analysis and design involve graphic languages or set of symbols.

• These symbols are used according to certain rules of methodology for communicating the complex relationships

•

Why do we model/modeling??

• To test a physical entity before actually building it. • To set the stage for communication between customers

and developers.

• For visualization i.e. for finding alternative representations.

• For reduction of complexity in order to understand it.

Object Oriented Methedologies

Object Oriented Methedologies

Introduction.. To OOM• Object Oriented Methodology (OOM) is a new system

development approach encouraging and facilitating reuse of software components

• OOM requires that object-oriented techniques be used during the:– analysis, – design and – implementation of thesystem.

• This methodology makes the analyst to determine :– what the objects of the system are,– how they behave over time or in response to events,– and what responsibilities and relationships an object has to

other objects.

steps

• The basic steps of system designing using OOM are:

– System Analysis – System Design – Object Design – Implementation

(Object -Oriented)Analysis- Design- Implementation

• Object-oriented analysis has the analyst:– look at all the objects in a system, – their commonalties, difference, and – how the system needs to manipulate the objects.

• During design:– overall architecture of the system is described.

• During implementation phase:– the class objects and the interrelationships of these classes

are translated and actually coded using the programming language.

– The databases are created and the complete system is made operational.

Advantages of OOM

• The systems designed using OOM are closer to the real world Because of this, it becomes easier to produce and understand designs.

• The objects in the system are immune to requirement changes because of data hiding and encapsulation features of object-orientation. •

• OOM designs encourage more reusability. The classes once defined can easily be used by other applications..

• Another way of reusability is provided by the inheritance feature of the object-orientation.

Advantages of OOM

• Object Oriented Methodology closely represents the problem domain. Because of this, it is easier to produce and understand designs.

• Object Oriented Methodology approach is more natural. It provides nice structures for thinking and abstracting and leads to modular design.

Popular OOM

• Booch Methodology [1994]: He developed the Object Oriented Analysis and Object Oriented Design (OOA/OOD) concepts.

• RDD Methodology [1990]: Wirfs-Brock, Wilkerson, and Wiener developed Responsibility Driven Design (RDD) methodology.

• OMT methodology [1991]: James Rumbaugh led a team at research labs of General Electric to develop the Object Modeling Technique (OMT).

• OOSE [1994]: Ivar Jacobson developed the Object Oriented Software Engineering (OOSE).

Models supported by OMT

• Object/static Model - This model describes the objects in a system and their interrelationships. This model observes all the objects as static and does not pay any attention to their dynamic nature.

• Dynamic Model - This model depicts the dynamic aspects of the system. It portrays the changes occurring in the states of various objects with the events that might occur in the system.

• Functional Model - This model basically describes the data transformations of the system. This describes the flow of data and the changes that occur to the data throughout the system.

Summary of Unit 1

• We learned about:– Object Oriented Concepts:

• Abstraction• Encapsulation• Hierarchy• Modularity• Polymorphism• Typing, persistency,

concurrency

– Object:• State• Behavior• Identity• Roles and responsibility• Life time

• Object Oriented Development

• Object Oriented Methodology

• Object modeling technique(introduction):• Object/ static

modeling• Dynamic modeling• Functional

modeling

Course Outcome Mapping

• Unit 1: Introduction – The successful completion

contributed towards partial achievement of :

• Course outcome 1 • Course outcome 3

End of Unit 1End of Unit 1