OODIAGRAMS (4).ppt
- 1. 3. Analysis Overview of OO concepts Classes and objects Finding classes Class Diagram
- 2. 3.2 Classes and Objects Classes Associations (Static Modelling)
- 3. Classes and Objects • 1 Classes & Objects • 2 The Class Diagram • 3 Associations • 4 Aggregation & Composition • 5 Generalisation
- 4. Classes and Objects • Classes, Objects and their relationships are the primary way to model. • A class is like a type and therefore an object is like a variable.
- 5. An Object has ... • Attributes (data). • Behaviour (operations). • State (memory) • Identity • Responsibilities
- 6. An example Object ... • A sensor: – Attributes (data): Value, Rate of change – Behaviour (operations): acquire, report ... – State (memory) Last value, Last Rate – Identity: Robot arm joint sensor – Responsibilities: Gives co-ordinates for arm
- 7. The Class: Sensor • All sensors share certain characteristics hence we have a class of sensors. • But each individual example is an object. • (An instance of the class)
- 8. Attributes • Describe the state and characteristics of the object. • Must be typed, primitives like integer, real, Boolean, point, area, enumeration. May be language specific. • Visibility may be public (+), private (-) or protected (#).
- 9. Attributes (Contd.) • Class variables have scope across every instance of class, change one changes all. • Property strings may be used to define allowable properties of an attribute. Used for enumeration types. • Syntax – visibility name : type-expression = initial-value {property-string} • Only name and type are mandatory.
- 10. Example Class Sensor + Linear_Value :Real + Rate_Of_Change : Real = 0.0 + Sensor_Name : String + Sensor_Location: String - Controller: String = “Unspecified” - number_of_sensors: Integer + status: Status = ON{ON, OFF} Name, bold Public, typed Default value Class variable Private, typed, default value Property
- 11. Operations • Operations manipulate attributes and perform other tasks. • Scope is the Class. • Operation signature is composed of name, parameters and return type. – name(parameter-list) return-type-expression • Scope and visibility rules apply.
- 12. Syntactic Constructs • Formal syntax is as follows – visibility name(parameter-list) return- type-expression {property-string} • parameter-list specified as … – name: type-expression=default-value • All operations must have unique signature. • Default values on parameters are Ok.
- 13. Figure -size: Size -pos: Position +figCounter: Integer +draw() +resize(percentX: Integer=25, percentY=30) +returnPos(): Position incCounter(): Integer MyFigure.resize(10,10) MyFigure.resize(27) MyFigure.resize() percentX=10, percentY=10 percentX=27, percentY=30 percentX=25, percentY=30 Signatures ? Class scope ? Defaults ? On the Class Diagram
- 14. Cardinality Examples Rent Member Video Employee Name:String Number:EmpNo Dept Name:Name Has Customer Account AccNo:Account Balance: Real 1..* 0..1 *
- 15. Class & Object Representation Rent Member Video Sunset Boulevard: Video Night for day: Video John Doe: Member 0..1 *
- 16. Navigable Associations • Used to indicate responsibility, later may be translated into pointer mechanism. • May be bi-directional. Person Car owns 0..*
- 17. Recursion • Self referential construct. • Complex construct, may not be supported by target language. User Directory container contents owner authorised user * * * * 0..1
- 18. Qualified Associations • A qualified association relates two Object Classes and a “qualifier”. • One-to-many and many-to-many associations may be qualified. • The qualifier distinguishes among the set of objects at the “many” end of an association.
- 19. Directory File Is more clearly expressed as ..... Directory File File name * Qualified Associations
- 20. Or-Association • A constraint on two or more associations. • Objects of a class may participate in at most one of the associations at a time. Insurance Co Insurance Contract Person Company 1 0..* {or} 0..* 1..* 1..*
- 21. Ordered Association • Shows implicit order of associations. • Default is unordered. Window Screen Controller Sensor {ordered} {ordered} Visible on polls * *
- 22. Association Class • Class may be attached to association, and not another class. Person Company Employment Period: dateRange * 0..1 Association Class employer
- 23. Shared Aggregation Team Person Members * * • One person may be a member of many teams. • Person is part of team, shared by N teams.
- 24. Composition Aggregation • More restrictive. Strong ownership here. • Rules – Parts live inside whole, parts die with whole, like automatic variables. – Multiplicity on whole side must be “0..1”, on part side may be anything. • Composition aggregation forms a tree of parts, shared forms a network of parts.
- 26. Text Listbox Button menu Window * * * * • Component not bold. • May use syntax – rollname:classname • Multiplicity shown.
- 27. Generalisation • Generalisation and Inheritance allow sharing of similarities among Classes while also preserving differences. • Inheritance refers to mechanism of sharing attributes & operations between subclasses and their superclass. • Default values of attributes & methods for operations may be overridden in subclass.
- 28. Example Financial service Mortgage Personal Loan Insurance Pension General Specific
- 29. Subclass Concretises FormControl ButtonElement InputElement Display(){abstract} Display() Display()
- 30. Implementation Issue FormControl ButtonElement Display(){abstract} Display() Display() Client Display() • When Client invokes Display(), method is bound at runtime. • Like pure virtual function in C++. InputElement
- 31. Constrained Generalization • Generalisations may be – Overlapping: inherit multiple subclasses with common superclass. – Disjoint: opposite to overlapping. – Complete: all subclasses specified, no more allowed. – Incomplete: more subclasses may be added to hierarchy.
- 32. Engineering Process for Allocation of Responsibility • Process will lay down rules for timing of allocation of responsibilities to classes from use cases. • May use domain analysis, find classes & relationships, then allocate from use cases. • May find classes from use cases.
- 33. Domain Analysis • Use Natural Language Problem Domain Natural Language
- 34. Class Description • Develop a Class description, either in textual prose or some other structured form. E.G. using a customer in a Bank – Customer: a holder of one or more accounts in a Bank. A customer can consist of one or more persons or companies. A customer can: make withdrawals; deposit money; transfer money between their accounts or to another account; query their accounts.
- 35. Structured Class Description Class Name: Customer Description: Personal or company details Superclass: User Name: Name Description: Customer’s name Type: String (max. 12 chars) Cardinality: 1 Name: Owns Description: Details of bank accounts Type: Account Cardinality: Many
- 36. Structured Class Description (cont..) Public Methods: Name: Pay_bill Parameters: amount, date, destination, account. Description: Customer may pay bills through the Bank.
- 37. Class Diagram Customer Portfolio Trader Instrument Bond Stock Stock Option 0..* 0..* contains 1 1..* owns handles 1..* 1
- 38. Class Diagram Notation • Depicts static structure of classes. • Classes represent things in the system. • Classes may be related in many ways… – Associated – Dependant – Specialised – Packaged
- 39. Object Diagram Author Name:String age:integer Computer Name:String memory:integer uses 0..1 1..* Class Diagram Brian:Author Name=“bstone” age=38 Laptop:Computer Name=”DellLT” memory=32 Desktop:Computer Name=“DellMMX” memory=32 Object Diagram