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Software Engineering
Project Management
Module 2
Introduction, Modelling Concepts and Class Modelling: What is Object orientation? What is OO development? OO Themes; Evidence for usefulness of OO development; OO Modelling history. Modelling as Design technique: Modelling, abstraction, The Three models. Class Modelling: Object and Class Concept, Link and associations concepts, Generalization and Inheritance, A sample class model, Navigation of class models, and UML diagrams. Building the Analysis Models: Requirement Analysis, Analysis Model Approaches, Data Modelling Concepts, Object Oriented Analysis, Scenario-Based Modelling, Flow-Oriented Modelling, class Based Modelling, Creating a Behavioural Model. Presented By: Dr. Prakhyath Rai
Introduction
Object oriented means organizing software as a collection of discrete objects that incorporate both
data structure and behaviour.
Characteristics of OO approach:
▪ Identity - Data is quantized into discrete, distinguishable entities called object. Examples: first paragraph, a white rook etc. ▪ Classification - Objects with the same data structure (Attributes) and behaviour (Operations) are grouped into a class. Examples: Student, Paragraph ▪ Inheritance - Sharing of attributes and operations (Features) among classes based on a hierarchical relationship. A superclass has general information that subclass refine and elaborate. Example: Window ( Superclass ) - > ScrollingWindow + FixedWindow ( Subclasses ) ▪ Polymorphism - Same operation may behave differently for different classes. Example: Move operation of Queen and Move operation of Pawn. Operation: Procedure or transformation an object performs or subjected to Method: An implementation of an operation by a specific class
OO Development
- OO Methodology ▪ System Design – High level strategy: The System Architecture ▪ Class Design – Adds details to system design analysis model, Focus on data structures and algorithms for each class ▪ Implementation – Translates classes and relationships from class design into a particular programming language
- Three Models – To describe systems from different viewpoints
▪ Class Model – Describes static structure of the objects in the system and their relationship ( Class
Diagram )
▪ State Model – Describes the aspects of the object that change over time ( State Diagram )
▪ Interaction Model – Describes how objects in the system cooperate to achieve broader results ( Use-Case
Diagram , Sequence Diagram , Activity Diagram )
OO Themes
1. Abstraction ▪ Abstraction means focusing on what an object is and does, before deciding how to implement it. ▪ Focussing on what an object is and does, before deciding on implementation 2. Encapsulation ▪ Information Hiding - separates the external aspects of an object that are accessible to other objects, from the internal implementation details that are hidden from other objects. 3. Combining Data and Behaviour ▪ The caller of an operation need not consider how many implementations exist. ▪ Operator polymorphism shifts the burden of deciding what implementation to use from the calling code to the class hierarchy.
Evidence for Usefulness of OO Development
1. Testing a physical entity before building it
2. Communication with Customers
3. Visualization
4. Reduction of Complexity
Abstraction:
▪ Selective examination of certain aspects of a problem.
▪ The goal of abstraction is to isolate those aspects that are important for some purpose
and suppress those aspects that are unimportant.
▪ A good model captures the crucial aspects of a problem and omits the others.
The Three Models
Model a system with related but different viewpoints
1. Class Model
▪ Represents the static, structural and data aspects of a system
2. State Model
▪ Represents the temporal, behavioural, control aspects of a system
3. Interaction Model
▪ Represents the collaboration of individual objects, interaction aspects of a system ➢ The 3 kinds of models separate a system into distinct views. ➢ Example: Class model attaches operations to classes and state and interaction models elaborate the operations
State Model ▪ Describes those aspects of objects concerned with time and the sequencing of operations – events that mark changes, states that context for events and the organization of events and states. ▪ State diagrams express the state model. Each state diagram shows the state and event sequences permitted in a system for one class of objects. ▪ The state model captures control , the aspect of a system that describes the sequence of operations that occur, without the regard for what the operations do, what they operate on, or how they are implemented.
Interaction Model
▪ Describes interactions between objects – how individual objects collaborate to
achieve the behaviour of the system.
▪ Use cases, sequence diagrams and activity diagrams document the interaction model.
- Use cases document major themes for interaction between the system and outside
actors.
- Sequence diagrams show the objects that interact and the time sequence of their
interactions.
- Activity diagrams show the flow of control among the processing steps of a
computation.
Class Modelling - Concepts ▪ Class & Object Diagram ▪ Association & Links ▪ Multiplicity ▪ Multiplicity & Visibility of Attributes ▪ Association End Names ▪ Association Classes ▪ Qualified Associations ▪ Ordering, Bags & Sequence ▪ Generalization and Inheritance ▪ Overriding Features
Sample Class Diagrams
Sample Class Diagrams Objects
Sample Class Diagrams
Sample Class Diagrams Class Model for Managing Credit Card Accounts
Navigation of Class Model - OCL Attributes: You can traverse from an object to an attribute value. ▪ Syntax: source object, followed by a dot and then the attribute name. ▪ Example: aCreditCardAccount. maximumCredit Operations: You can also invoke an operation for an object or a collection of objects. ▪ Syntax: source object or object collection, followed by a dot and then the operation. The operation must be followed by parentheses, even if it has no arguments to avoid confusion with attributes. ▪ The OCL has special operations that operate on entire collections. The syntax for a collection operation is the source object collection followed by - > and then the operation.
