Chapter 11

Object-Oriented DBMSsObject-Oriented DBMSs

Chapter 27, 28 & Appendix K in Textbook

2

Advanced Database ApplicationsAdvanced Database Applications

• Computer-Aided Design (CAD).

• Computer-Aided Manufacturing (CAM).

• Computer-Aided Software Engineering (CASE).

• Network Management Systems.

• Office Information Systems (OIS) and Multimedia Systems.

• Digital Publishing.

• Geographic Information Systems (GIS).

• Interactive and Dynamic Web sites.

• Other applications with complex and interrelated objects and procedural data.

OODBMS

3

Weaknesses of RDBMSsWeaknesses of RDBMSs

• Poor Representation of “Real World” Entities.

• Semantic Overloading.

• Poor Support for Integrity and Enterprise Constraints.

• Homogeneous Data Structure.

• Limited Operations.

• Difficulty Handling Recursive Queries.

• Impedance Mismatch.

• Other Problems with RDBMSs:o Transactions are generally short-lived and concurrency control protocols not

suited for long-lived transactions.

o Schema changes are difficult.

o RDBMSs are poor at navigational access.

OODBMS

4

Example - Recursive QueryExample - Recursive Query

S005S004S003S002S001S005S005S005S004S004S003

S004S003S002S001NULLS003S002S001S002S001S001

StaffNo

S005S004S003S002S001

S004S003S002S001NULL

MangrsSNo MangrSNoStaffNo

OODBMS

5

What is an OODBMS ?What is an OODBMS ?

OODBMS

OODBMS (Object-oriented Database Management System): is a database

with data stored in objects and collections NOT rows and tables.

Object Oriented Concepts:

Abstraction, encapsulation, and information hiding.

Objects and attributes.

Object identity.

Methods and messages.

Classes, subclasses, superclasses, and inheritance.

Overriding, Overloading, Polymorphism and Dynamic Binding.

OODBMS 6

Traditional DBS

•Persistence•Sharing•Transactions•Concurrency Control•Recovery Control•Security•Integrity•Querying

Semantic Data Model

•Generalization•Aggregation

OO Programming

•OID•Encapsulation•Inheritance•Types & Classes•Methods•Complex objects•Polymorphism•Extensibility

Special Requirements

•Versioning•Schema Evolution

OODBMS

OODBMSOODBMS

7

AbstractionAbstraction

Abstraction is the process of identifying essential aspects of an entity and

ignoring unimportant properties.

Concentrate on what an object is and what it does, before deciding how to

implement it.

OODBMS

8

Encapsulation & Information HidingEncapsulation & Information Hiding

Encapsulation: means that an object contains both data structure and set

of operations used to manipulate it.

Information Hiding: means separating external aspects of an object from

its internal details, which are hidden from outside.

• Allows internal details of an object to be changed without affecting applications

that use it, provided external details remain same.

• Provides data independence.

OODBMS

9

ObjectsObjects

Object is a uniquely identifiable entity that contains both:

• the attributes that describe the state of a real-world object,

• and the actions associated with it.

Definition very similar to that of an entity, however, Object encapsulates

both state and behavior; an entity only models state.

Persistent Objects vs. Transient Objects:

• Transient: object’s memory allocated and deallocated by programming language’s runtime system.

• Persistent: object’s storage managed by OODBMS.

OODBMS

10

AttributesAttributes

Attributes contain current state of an object:

• Attributes can be classified as simple or complex.

• Simple attribute can be a primitive type such as integer, string, etc.,

which takes on literal values.

• Complex attribute can contain collections and/or references.

• Reference attribute represents relationship.

• An object that contains one or more complex attributes is called a

complex object.

OODBMS

11

Object Identity (OID)Object Identity (OID)

Object identifier (OID) assigned to object when it is created that is:

• System-generated.

• Unique to that object.

• Invariant.

• Independent of the values of its attributes (that is, its state).

• Invisible to the user (ideally).

OODBMS

12

Object Identity (OID)Object Identity (OID)

In RDBMS, entity identity is value-based: primary key is used to provide

uniqueness.

Primary keys do not provide type of object identity required in OO

systems:

• key only unique within a relation, not across entire system;

• key generally chosen from attributes of relation, making it dependent

on entity state.

OODBMS

13

Methods & MessagesMethods & Messages

Method: Defines behavior of an object, as a set of encapsulated

functions.

Message: Request from one object to another asking second object to

execute one of its methods.

OODBMS

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Object Showing Attributes & Object Showing Attributes & MethodsMethods

Attributes

Method 4 Method 3

Method 2Method 1

OODBMS

15

ClassesClasses

Classes are blueprints for defining a set of similar objects.

• Objects in a class are called instances.

• Class is also an object with own class attributes and class methods.

• Object created from the same class share the same class attributes

and methods.

OODBMS

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Class Instance Share Attributes & Class Instance Share Attributes & MethodsMethods

BRANCH

BranchNo = B005Street = 22 Deer RdCity = LondonPostcode = SW1 4EH

BranchNo = B007Street = 16 Argyll StCity = AberdeenPostcode = AB2 3SU

BranchNo = B003Street = 163 Main StCity = GlasgowPostcode = G11 9QX

Attributes

branchNostreetcitypostcode

Methods

print()getPostCode()numberOfStaff()

OODBMS

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Subclasses, Superclasses, & Subclasses, Superclasses, & InheritanceInheritance

Inheritance allows one class of objects to be defined as a special case of

a more general class.

•Special cases are subclasses and more general cases are superclasses.

•Process of forming a superclass is generalization; forming a subclass is

specialization.

•Subclass inherits all properties of its superclass and can define its own unique

properties.

•Subclass can redefine inherited methods (overriding).

•Relationship between subclass and superclass known as A KIND OF (AKO)

relationship.

OODBMS

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Subclasses, Superclasses, & Subclasses, Superclasses, & InheritanceInheritance

Types of inheritance: single, multiple, and repeated.

OODBMS

Single Inheritance Multiple Inheritance Repeated Inheritance

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Overriding, Overloading & Overriding, Overloading & PolymorphismPolymorphism

Overriding is the process of redefining a property within a subclass.

Overloading allows name of a method to be reused with a class or across

classes.

Polymorphism means ‘many forms’. Three types: operation, inclusion, and

parametric.

The process of selecting the appropriate method based on an object’s type is called binding.

• If the determination of an object’s type can be deferred until runtime (rather than compile time), the selection is called dynamic binding.

OODBMS

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Complex ObjectsComplex Objects

A Complex object is something that can be viewed as a single object in the

real world but it actually consists of many sub-objects.

Two types of complex objects:

•Unstructured complex objects:

• Their structure hard to determine.

• Requires a large amount of storage.

• BLOB (Binary Large Objects): images & long test strings.

•Structured complex objects:

• Clear structure.

• Sub-objects in A PART-OF (APO) relationship.OODBMS

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Structured Complex ObjectsStructured Complex Objects

The contained object can be handled in one of two ways:

• Contained object can be encapsulated within complex object, accessed

by complex object’s methods.

• Or have its own independent existence, and only an OID is stored in

complex object.

OODBMS

Obj 2

Contains a number of unnamed, homogeneous elements; each can be

instance of atomic type, another collection, or a literal type.

Types of Constructors:

Set: unordered collection of objects without duplicates.

Bag: unordered collection of objects that allows duplicates.

List: ordered collection of objects that allows duplicates.

Array: ordered collection of objects without duplicates.

Dictionary: unordered sequence of key-value pairs without duplicate keys.

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CollectionsCollections

OODBMS

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Commercial OODBMSsCommercial OODBMSs

• GemStone from Gemstone Systems Inc.,

• Itasca from Ibex Knowledge Systems SA,

• Objectivity/DB from Objectivity Inc.,

• ObjectStore from eXcelon Corp.,

• Ontos from Ontos Inc.,

• Poet from Poet Software Corp.,

• Jasmine from Computer Associates/Fujitsu,

• Versant from Versant Object Technology.

OODBMS

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Object Data Management Group (ODMG)Object Data Management Group (ODMG)www.odmg.orgwww.odmg.org

ODMG is an international consortium founded to address object standards.

Major components of ODMG architecture for an OODBMS are:

• Unified Modeling Language (UML).

• Object Model (OM).

• Object Definition Language (ODL).

• Object Query Language (OQL).

• C++, Smalltalk, and Java Language Binding.

OODBMS

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Unified Modeling Language (UML)Unified Modeling Language (UML)

UML is a standard language for specifying, constructing, visualizing, and

documenting the artifacts of a software system.

•Include many structural diagrams (Class, Object diagrams…) and behavioral

diagrams (UseCase, Sequence diagrams…).

•Used to model objects and object relationships.

OODBMS

Class Name

Attribute

Method

MANAGERStaffNosexDOBsalary

increasesalary()

PROPERTYPropertyNostreetcitypostcoderoomstype

1..1 manage 1.1 1..1 offer 1.*

offered-by

Association

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Unified Modeling Language (UML)Unified Modeling Language (UML)

OODBMS

PERSONName FName LName

STAFFStaffNopositionDOBsalary

POWNEROwnerNoaddress

CLIENTClientNotelNOprefTypeMaxRent

MANAGER SALESTAFF

BRANCH

PROPERTYPropertyNoroomsrent

BranchNoaddress

Manages

WorksAt

Offers

ViewsOwns

1

11

M

1

M

1

M M

N

ManagedBy

Has

OwnedBy

IsOfferedBy

ViewedBy

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Object Model (OM)Object Model (OM)

Object Model (OM) provides the data type, type constructors & other

concepts utilized in the ODL to specify the object schema.

•Basic building blocks are object and literal.

•Only an object has a unique identifier and state (current value).

•Literal is a constant values. e.g. “Ahmed”, “123 Main St, London” .

•Behavior defined by set of operations that can be performed on or by

object.

•State defined by values objects carry for a set of attributes of object or

relationships between object and one or more other objects.

OODBMS

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Object Definition Language (ODL)Object Definition Language (ODL)

Object Definition Language (ODL) is a language for defining the specification

of object types for OODBMS. e.g. of ODL definition for DreamHome:

OODBMS

module DreamHome {

Class Branch (extent branchOffices key branchNo)

{

attribute string branchNo;

attribute struct BranchAddress {string street, string city, string postcode} address;

relationship Manager ManagedBy inverse Manager::Manages;

relationship set<SalesStaff> Has inverse SalesStaff::WorksAt;

relationship set<PropertyForRent> Offers inverse PropertyForRent::IsOfferedBy;

void takeOnPropertyForRent(in string propertyNo) raises(propertyAlreadyForRent);

}; };

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Object Query Language (OQL)Object Query Language (OQL)

Object Query Language OQL is a query language for OODBMS.

• Does not provide explicit update operators - leaves this to operations

defined on object types.

OQL can be used for both associative and navigational access:

• Associative query returns collection of objects (like SQL).

• Navigational query accesses individual objects and object relationships

used to navigate from one object to another.

OODBMS

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Object Query Language (OQL)Object Query Language (OQL)

OQL vs. SQL A Simple Example: List the names of the children of

employees working in the sales department.

OODBMS

select

c.fname, c.lname

from

Department d, d.Employee e,

e.Children c

where

d.name = “Sales”;

select

c.fname, c.lname

from

Department d, Employee e,

Children c

where

d.name = “Sales” and

d.deptID = e.deptID and

c.parentID = e.empID;

OQL SQL