OODB CONCEPT

8/8/2019 OODB CONCEPT

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Object Oriented Databases

Software Engineering Department


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2

Lecture outliney Object-Oriented concepts

y Objects, Classesy Attributes, Operations, Associationsy Encapsulation, Inheritance

y Unified Modelling Language

y Object-Oriented Data Modellingy Identifying

y Classes, attributes, and operations.y Associations among classes

y

Drawing class diagramsy Normalization

y Introduction to ODMG 3.0 (the standard for Object-OrientedDatabases)


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Object-oriented databases

y Avoid object-relational impedance mismatch

y Provide a uniform data model

y Combine features and properties of object-orientedsystems and languages


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Object-oriented concepts

y Objectsy Objects represent real world entities,

concepts, and tangible as well asintangible things.y For example a person, a drama, a licence

y Every object has a unique identifier (OID).y A memory addressy System generatedy Never changes in the lifetime of the object


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y Objectsy An object is made of two things:

y State: attributes (name, address, birthDate of a person)y Behaviour: operations (age of a person is computed from

birthDate and current date)y Objects are categorized by their type or class.y An object is an instance of a type or class.


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y Sharing of objects through references

y Two objects are identical if they have the same OID

y Two objects are equal if they have the same state


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y Classificationy Classification is the process of grouping together objects

which have common features.y Programming languages have type systems and database

systems have data models to classify object.y The name used for the classificatory group of values is

usually called class .

y

Classy Provides a template for constructing objects.y Instances of a class have the same kind of data and

identical behaviour.


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y An Example of a class in UM L

name: {Norman, William, Preston}address: StockportbirthDate: 11-JUN-70

Person

name: {firstName: string,middleName: string,lastName: string}

address: stringbirthDate: date

age(): Integer changeAddress(newAdd: string)

Class Name

Attributes

Operations

p:Person A Person object


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y Encapsulationy Merger of data structure and

operations.y Objects are composed of attributes

(values) and operations(behaviour).


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y Inheritancey A class can be defined

in terms of another one.y Person is super-class

and Student is sub-class.y

Student class inheritsattributesand operations of Person.

Person

name: {firstName: string,

middleName: string,lastName: string}address: stringbirthDate: date

age(): Integer changeAddress(newAdd: string)

Student

regNum: string {PK}

register(C: Course): boolean

major: string


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Why ODBs?

ODBs are inevitable when:Data is complex and variable in sizeComplex structural and compositional relationshipsData is highly inter-relatedData is evolving rapidly over timeRicher data types

complex objectsinheritanceuser extensibility

Behaviour with datanot just a data model but alsooperations can be bundled together with data


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Compari s on c ontinued

RDB s vs. O DB s.Not very easy to compare because of philosophical differences.RDBs have only one construct i.e.Relation, whereas the type system of ODBs is much richer and complex.RDBs require primary keys and foreignkeys for implementing relationships, ODBs

simply dont.


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Compari s on c ontinued

RDB s vs. O DB s.ODBs support complex data whereasRDBs dont.ODBs support wide range of applications.ODBs are much faster than RDBs but areless mature to handle large volumes of data.There is more acceptance and dominationof RDBs in the market than that for ODBs.


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UML


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Defining Class A CLASS is a template (specification, blueprint)for a collection of objects that share a common

set of attributes and operations.

HealthClubMember

Class

Objects

attributesoperations


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R elationships A RELATIONSHIP is what a class or an object

knows about another class or object.

G eneralization (Class-to-Class) (Superclass/Subclass) InheritanceEx: Person - FacultyPerson, StudentPerson, Staff...

Ex: ModesOfTravel - Airplane, Train, Auto, Cycle, Boat...[ Object] Associations

FacultyInformation - CourseInformationStudentInformation - CourseInformation

[ Object] Aggregations & Composition (Whole-Part) Assembly - Parts

G roup - MembersContainer - Contents


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U ML Class Diagram Notation

M ember

memberNumberfirstNamelastNametelephoneaddresscityetc...

checkOutVideocheckInVideobuyItemetc...

attributes

operations

{{

Expanded view of aClass into its three

sections:

Top: Class Name

Middle: attributes

Bottom: operations

Class


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Generalization Relationships

P ersonA generalization connects a subclassto its superclass. It denotes aninheritance of attributes and behaviorfrom the superclass to the subclass andindicates a specialization in the subclassof the more general superclass.

Student


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22G eneralization (Class-to-Class)(superclass subclass; supertype subtype)

y A G eneralization follows a is a or is a kind of heuristic from aspecialization class to the generalization class. (e.g., student is aperson, video is a kind of inventory).

y Common attributes, operations and relationships are located in the

generalization class and are inherited by the specialization classesy Unique attributes, operations and relationships are located in the

specialization classes.


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Person

attributes

operations

Poor G eneralization Example(violates the is a or is a kind of heuristic)

A rm

attributes

operations

L eg

attributes

operations

Head

attributes

operations


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Associations

R elationships between instances(objects) of classesConceptual:

associations can have two roles (bi-directional):

source --> target target --> source

roles have multiplicity (e.g., cardinality, constraints)To restrict navigation to one direction only, anarrowhead is used to indicate the navigation direction

No inheritance as in generalizations


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Multiplicity of Associationsy Multiplicity: refers to how many objects of one class can relate

to each object of another class.

Symbols used to indicate multiplicity in associations:

Class

Class

Class

Class

Exactly one

Zero or more*

0..1 Optional (0 or 1)

1.. * One or more


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Software Design (UML)

Association Relationships

If two classes in a model need tocommunicate with each other, there mustbe link between them.

An association denotes that link.

InstructorStudent


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Association Relationships (Contd)

We can indicate the mu ltiplicity of an association by addingmu ltiplicity adorn m ents to the line denoting the association.

The example indicates that a St u dent has one or more Instr u ctors :

InstructorStudent 1 ..*


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The example indicates that every Instr u ctor has one or moreSt u dents :

InstructorStudent 1 ..*


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We can also indicate the behavior of an object in an association( i.e., the role of an object) using rolena m es.

InstructorStudent 1 ..*1 ..*

learns fromteaches


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We can also name the association.

TeamStudentmembership

1 ..* 1 ..*


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We can constrain the association relationship by defining thenavigability of the association. Here, a Ro u ter object requestsservices from a DNS object by sending messages to (invoking theoperations of) the server. The direction of the association indicatesthat the server has no knowledge of the Ro u ter .

R outerDomainNameServer


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Associations can also be objects themselves, called link classes oran association classes .

WarrantyP roduct

R egistration

modelNumberserialNumberwarrentyCode


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We can model objects that contain other objects by way of specialassociations called aggregations and co m positions.

An aggregation specifies a whole-part relationship between anaggregate (a whole) and a constituent part, where the part canexist independently from the aggregate. Aggregations are

denoted by a hollow-diamond adornment on the association.

Car

Engine

Transmission


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A co m position indicates a strong ownership and coincidentlifetime of parts by the whole ( i.e., they live and die as a whole).Compositions are denoted by a filled-diamond adornment on theassociation.

Window

Scrollbar

Titlebar

Menu

1

1

1

1

1

1 ..*


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Inventory

Video Store UML Class Diagram

SaleItem R entalItem

Video Game ConcessionItem VCR

Transaction Employee StoreLocation

SaleTransaction R entalTransaction Suplier

Member P urchaseOrder

Sale R entalLineItemP urchaseOrderLineItem

1

0..*

0..* 0..1 10..*

1..*

1 1

1..*

10..*

10..*

11..*

1 0..*

0..*

1

OODB CONCEPT

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