OBJECT-ORIENTEDNESS

What isObject-Orientedness?

model system as a collection ofinteracting objects

O-O Modelling O-O Programming

► similar conceptual philosophy

► different purpose

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Objectswhat is an object?

individuality

properties

►real world thing - something tangible

►conceptual / virtual / abstract

►all objects have identity

►all objects are distinguishable - twins

►identity - state – behaviour

►(identity - data - operations)

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there are many THINGS in the world

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From: Sigfried S (1996). Understanding Object-Oriented Software Engineering

the World our Model

From: Sigfried S (1996). Understanding Object-Oriented Software Engineering5/26

Objects (cont..)

individual, identifiable entity (real or abstract)

with a well defined rolein the problem domain

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Object Propertiesidentity

state (data)

behaviour (operations/methods)

► property of an object which distinguishes it from all other objects

► attributes of an object

► attributes have values

► describes how object acts & reacts

► procedures / operations (messages)

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Object Properties(cont.)

attributes (data)

behaviour (operations/methods)

► descriptor (variable) that holds value e.g. name, weight, colour, model,

► may have same across classes e.g. weight

► procedure that may be applied to or by an object

e.g. Move, Open, Draw, ...

► all objects in a class share same operations

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Classes and Instancesinstance (object)

class

► unique individual

► all values unique

► individuality from differences in attribute values (but may differ in only location & orientation)

► abstraction - generalization

► group of objects with common properties

► differentiation in attributes

► attributes can have ranges / options

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similar THINGS can be GROUPED

From: Sigfried S (1996). Understanding Object-Oriented Software Engineering

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11/26From: Rumbaugh et al. (1991). Object-Oriented Modeling and Design

From: Rumbaugh et al. (1991). Object-Oriented Modeling and Design 12/26

Class Relationshipstaxonomical / typological

aggregation

others

► a_kind_of, a_type_of, is_a, an_instance_of ako, ato, isa, aio

► a_part_of, a_component_of apo, aco

► functional, ownership, connectivity, ... provides_access, owned_by, joins

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depends on purpose

Classificationbrings order

no simple recipe

► knowledge ordered hierarchically

► no perfect class structure & set of objects

► difficult - boundaries are fuzzy

► difficult to define precisely attributes & values e.g. cup and bowl

► different views

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Classification (cont.)

● superclass, subclass, instance

► general to specific

► fewer members - more specific

► ancestors - descendants

► parent - child

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Inheritance

superclass, subclass, instance

C1

superclass

instance

superclasssubclass

subclass

A

B

C

ato

ato

aio

recursive

reuse

► subclass inherits all properties of superclass

► instance special case of subclass

► inherit ‘up the line’

►avoids redundancy

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From: Rumbaugh et al. (1991). Object-Oriented Modeling and Design 17/26

vehicle

landvehicle

watervehicle

amphibiousvehicle

car boat

Multiple Inheritance

ato ato

atoato ato ato

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Generalization / Specialization

generalization

specialization

► extract common characteristics

► create higher-level abstraction

► bottom-up

► top-down

► may constrain ancestor attributes e.g. circle special case of ellipse

must do one of above

► add new features - extension e.g. hinged door adds swing behaviour

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Aggregation / Decomposition

assembly / component

recursive

structural hierarchy

► special form of relationship

► aggregate object made up of component objects

► treated as one unit - an object

► orthogonal concept to generalization/specialization

► components may be aggregations

► part/whole vs subclass/class

► apo, aco vs ako, ato, isa, aio

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lamp

fluorescentlamp

incandescentlamp

ballast starter socket

Aggregation / Decompositionaddition of components

base cover switch

ato

aco

acoaco

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lamp

fluorescentlamp

ballast starter

Aggregation / Decompositionaddition of components (cont.)

base cover switch

ato

aco

aco

L1

base1 cover1 switch1

aco

ballast1 starter1

isa

isaisa

isa

isaisa

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O-O Conceptsencapsulation / modularity

classification

inheritance

aggregation

► localize data & procedures in a module

► taxonomic / typologic hierarchy

► makes order

► reusability

► structural hierarchy

► hides / adds details

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O-O Languages● Smalltalk first popular OOL

● C++ strongly typed - lots of housekeeping

● Eiffel strongly typed - garbage collection

● CLOS (Common Lisp Object System) O-O extension of COMMON LISP encapsulation not enforced

● Objective C

● Java cleaned-up version of C++ - no pointers distributed 24/26

O-O Databasesdatabases

O-O programming

OODMS

► relationships

► used to store persistent data

► data doesn’t vanish when program stops execution

► objects

► not persistent

► object information persistent

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