Module Outline. What is Object-Oriented? Some Possible Definitions. Why Object-oriented? Fundamentals of Object Orientation

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1 Module Outline Fundamentals of Object Positioning Object Oriented Analysis Fundamentals of Object 1. Encapsulation 2. Abstraction 3. Inheritance 4. Polymorphism The need of Modeling Unified modeling language Mapping the UML to the Modeling Spaces 1 2 What is Object-Oriented? Some Possible Definitions Encompasses various aspects of software Development Analysis; Design; Implementation; Testing; Metrics; Databases; Architecture - especially Distributed; Management; Unlike Relational (set) Theory, has no Mathematical background; hence no Precise Definition; A good software engineering practice that attempts to address new IT challenges A good approach to build complex and rapidly changing software applications in the new millennium - Therefore, may apply to any software Development 3 4 Why Object-oriented? OO Software Engineering results in easier maintainability and extensibility Due to Localized and controlled changes OO Software Engineering results in more Opportunities for Reuse Code, Design (including Patterns and Frameworks), Requirements (Use cases), Components (Link time and Run time) 5 Positioning Objects within the Evolving Technical Thinking Savin gs Account g etintere s tdtls () Cheq u e Entity-Relationships; Data Flows; Flowcharts; SSADM Accou nt Cus tom er Booch etc. to Unified Modeling Language s 1990s 1980s 1970s 1

2 Positioning Objects In 1970 s Flowchart and Structured System Analysis and Design Methods In 1980 s Chen s popular Entity Relationship and Data Flow diagrams Early 1990 s Unified Modeling Language by Booch. 7 Object- (Components) + Distributed Computing + Global information systems Web-Services Based Internet Technologies Global Business Global IT Management 8 Learning and Adopting Object Fundamentals Modeling (UML Standard) Adopting OO Process Sub-Module Fundamentals of Object Basic Concepts Experience 9 10 Classes and Objects What is a Class? A CLOCK in general is a CLASS. Your CLOCK and My CLOCK are specific Objects A Class is a DEFINITION, a TEMPLATE, for the Objects NOTE: A Class is NOT a Collection of Objects; A class is not an individual object, represents a whole set of objects

3 Lithops Lesliei What is an Object? An Entity with crisply defined boundaries A physical or conceptual thing in the problem and the solution domain Identity is a unique identifier of an object Has attributes that describe the object, and also describe the state in which it exists Has behavior that is manifested in changes to the state of the object Sends and receives messages OO v/s Non-OO (Similarities and Differences) Non-Object-oriented (Traditional) Data and Procedures are kept Separate Procedures work on Data to produce results Object-oriented Focus on Responsibilities - to be satisfied by Objects Responsibilities translate into Data and Functions within a Object Objects have Behavior Procedures Data Procedures Data Comparing the Mindsets (Henderson-Sellers, Book of OO Knowledge, Prentice-Hall) Procedural Mindset What is the system supposed to do? What are the functions of the system? How do I design and code to achieve the functions? Focus is on the algorithms. OO Mindset What is the system made up of? Objects What are the responsibilities of these objects? How will these objects collaborate to satisfy the responsibilities? Algorithms/code deferred 15 The Star of OO Fundamentals ENCAPSULATION POLYMORPHISM CLASSIFIION Fundamentals of Object-: THE OBJECT ABSTRACTION INHERITANCE 16 Classification Classification Starting point of object orientation Grouping meaningful objects. Classification is based on the requirements appearing in the problem space

4 Abstraction: 1 st Level is from Objects to Class Abstraction: 2 nd Level is from Classes to Classes Can be Abstracted to ANIMAL HAT CLOCK Note that these are ABSTRACTIONS and not real Objects. Objects are Classified and good Classification leads to creation of good Abstractions. Classes that represent a collection of Objects are Abstract. CLOCK HAT Can be Abstracted to THING Classes are abstracted to higher level class Classification & Abstraction Requirements from Problem Space Can be Classified & Abstracted to Arrive at Good Classes MAN BOOK CHEST SHOE HAT Abstraction (and Classification).. Starts by grouping a given set of (reality) Objects based on certain characteristics Example: Marker Pens, Ballpoint Pens etc. From the classification (grouping), most common properties and behavior is abstracted to arrive at a Class definition Infinite number of objects can then be created (instantiated) from this Class Identifying more general groupings to create Inheritance Hierarchy Inheritance BIRD LIVING ANIMAL BIRD and ANIMAL are types of LIVING things MITHU? (my Bird) PUSPUS? (your Cat) Are Objects; They Don t appear on Class diagrams Inheritance in OO is the ability of a Class to inherit all attributes and behavior of a higher-level class Classifying with optimum granularity also leads to good inheritance structure CRANE

5 Inheritance Moving on the Inheritance Tree Child class inherits from parent class Child class shares the attributes and routines of parent class, plus perhaps adds additional features Child class can change implementation of parent class features multiple inheritance is permitted; some resolution for name clashes is required Finding Superclasses Needs abstract thinking Domain knowledge helpful Essentially FOR Reuse Finding Subclasses Concrete lower level implementation thinking Essentially WITH Reuse METHODS DATA (Attributes with States) Encapsulation Encapsulation means DATA is accessed only by METHODS BEGIN CODE END PUBLIC VISIBILITY PRIVATE INFORMATION Modularity (and Encapsulation).. When attributes of an Object are NOT accessed directly by any other Object within the system but only through the public interface of the Object, it is Encapsulation Objects are modularized to handle complexity, and encapsulation enhances the advantages by localizing changes to within the objects ANIMAL Polymorphism HORSE Advantage? CALLING object need not know what is Moved, so, if a new object is added, the CALLING class doesn t change On Receipt of Message move from a Calling Object, the appropriate move - depending on whether it is a Frog or a Horse - will be executed 29 Polymorphism.. Essentially the ability of an Entity to behave differently - even after receiving the same message Translates to the ability of the software to substitute different Objects at runtime Implemented via Inheritance in Objectorientation 30 5

6 Sub-Module The Need of Modelling Software Development Layers Purpose of Modelling: Understand and Create Reality (based on Unhelkar, B., 1999, 2003) Understand Reality Create Reality MODEL REALITY Modelling and Conceptual Software Development Layers (Place of UML) UML only deals with Modeling. It is NOT a Methodology (or a Process) Overall Management Quality Environment Management; Processes Methodologies Software Development Layers and Corresponding CASE TOOL Layer QSP; Process Continuum; Bpwin etc. RUP, OPEN, MeNtOR Modeling Languages, Databases Communication Technology TauG2; ROSE, Visio. Java, C++, XML, Oracle etc OO Models have a Small Semantic Gap (from Unhelkar, CRC Press, 1999) OO facilitates Seamless Transition from Problem to Solution Space (from Unhelkar, CRC Press, 1999) Class Passenger Class Flight Class Seat ANALYSIS Passenger Flight Seat Analysis (MOPS) Design (MOSS) Class Booking Priority Class DESIGN Class:: Passenger Class:: Flight Class:: Seat Implementation (MOSS)

7 Modelling Spaces and Roles in Analysis, Design and Architecture (A rough role-based guideline) Sub-Module Modeling Spaces And Relating them to the UML Model Of Problem Space (MOPS) Model Of Solution Space (MOSS)! " Model Of Background Space (MOBS)!! Exercises For Classroom Workbook Exercises 1. What is object orientation? What does it encompass? 2. How is object orientation different from procedural approach to software development? 3. What are the four major factors in learning and adopting object orientation? 4. List FIVE objects from your current surroundings. 5. Create at least TWO classes from the above five objects (This will help you understand the difference between a class and an object) Workbook Exercises 6. List next to each of the above TWO classes, at least FIVE attributes. 7. Discuss the importance of each of the fundamentals of OO within the context of software engineering. 8. What is a process and how it is different from modeling? 9. What are the two main reasons for creating models? 10. How is object-oriented modeling advantageous? 11. Name the three modeling spaces in OO modeling. Discuss the advantage of modeling in each of these three modeling spaces. Conclusions Software Development benefits with Process and Modeling; UML is OMG s standard for Modeling; OO has Five Fundamentals Classification; Abstraction; Inheritance; Encapsulation and Polymorphism Class is a Template; Object is an Instance; All Modeling Work happens in 3 Spaces: MOPS; MOSS; and MOBS