Chapter 1

Object-oriented DBMSs

Chapters 25-27 in Textbook

Overview

OODBMS2

Relational quick review Why OO? What is an Object? What is an object ID? Classes, subclasses and inheritance UML ODL OQL

Relational DBMS Quick Review

OODBMS3

Data model: ER.

Data is stored in tables. Each row is a record. Relationships between tables (PK-FK).

TakesStudent

Course

SID CID

namename

year

SID name

424112211

Nora M

424221122

Sara S

424331133

Hala L

SID CID year

Sem

424112211

CAP364 1425

1

424112211

CAP430 1426

2

424331133

CAP364 1426

1

Sem

CID name

CAP364

DB2

CAP430

Security

Weaknesses of RDBMS

OODBMS4

Poor Representation of “Real World” Entities.

Poor Support for Integrity and Enterprise

Constraints.

Homogeneous Data Structure.

Limited Operations.

Difficulty Handling Recursive Queries.

Schema changes are difficult.

RDBMSs are poor at navigational access.

Why OO? Advanced DB Applications

OODBMS5

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 – Read pages 805-808 in book.

What is an OODBMS anyway?

OODBMS6

OODBMS (Object-oriented DB Management System) is a database with data stored in objects and collections NOT rows and tables.

OO Concepts: Abstraction, encapsulation, information hiding.

Objects and attributes.

Object identity.

Methods and messages.

Classes, subclasses, superclasses, and inheritance.

Overloading.

Polymorphism and dynamic binding.

OODBMS

OODBMS7

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

Semantic Data Model•Generalization•Aggregation

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

Special Requirements•Versioning•Schema Evolution

OODBMS

Object

OODBMS8

Uniquely identifiable entity that contains both

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

and

the actions associated with it.

Object encapsulates both state and behavior; an entity only

models state.

Persistent objects vs. transient objects.

Everything in an OODBMS is an object.

Object Identity (OID)

OODBMS9

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).

OID Alternative 1

OODBMS10

In RDBMS, object identity is value-based: primary key is

used to provide uniqueness.

Why not use primary key in OODBMS?

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 object state (simulated key).

OID Alternative 2

OODBMS11

In OO programming languages, use variable names and

pointers/virtual memory addresses, which also compromise object

identity.

In OOPL, OID is physical address in process memory space, which

is

too small - scalability requires that OIDs be valid across storage

volumes, possibly across different computers.

Further, when object is deleted, memory is reused, which may cause

problems.

OID Advantages

OODBMS12

They are efficient.

They are fast.

They cannot be modified by the user.

They are independent of content.

Identical objects vs. equal objects

Encapsulation Object

OODBMS13

Attributes

Method 4 Method 3

Method 2Method 1

Class and Object (Instance)

OODBMS14

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()

Subclasses, Superclasses and Inheritance

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 (override).

All instances of subclass are also instances of superclass.

OODBMS15

Single Inheritance

OODBMS16

PERSON

STAFF

SALESSTAFF

MANAGER

Complex Objects A Complex object is something that can be

viewed as a single thing in the real world but it actually consists of many sub-objects.

2 Types: Unstructured.

Their structure hard to determine. Requires a large amount of storage. BLOB (Binary Large Objects): images & long test strings.

Structured. Clear structure. Sub-objects in a part-of relationship. Will talk more about in next slide.

OODBMS17

Structured Complex Objects

An object that consists of sub-objects but is viewed as a single object.

Objects participate in a A-PART-OF (APO) relationship.

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.

OODBMS18

M1

M3

M2

M4

Obj 2

Obj 1

Obj 2M1

M3

M2

M4

Obj 1

OID 2M1

M3

M2

M4

Obj 3

OID 2

Commercial OODBMs

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.

OODBMS19

Components of OODBMS

Object Model (OM): abstract modeling of objects and

relationships.

Unified Modeling Language (UML): used to describe OM.

Object Definition Language (ODL): language to specify the

schema for an OODBMS.

Object Query Language (OQL): Language to query an OODBMS.

C++, Smalltalk, and Java Language Binding.

OODBMS20

Object Model -- Collections 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.

OODBMS21

OM – Object Relationships A relationship between 2 objects can be:

One-to-One One-to-Many Many-to-Many

UML (Unified Modeling Language) is used to model objects and object relationships.

OODBMS22

UML Example

OODBMS23

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

Object Definition Language -- ODLmodule 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);

};

OODBMS24

ODLclass Person {

attribute struct Pname {string fName, string lName} name;};

Class Staff extends Person(extent staff key staffNo)

{attribute staffNo;attribute enum SexType {M, F} sex;;attribute date DOB;

short getAge();Void increaseSalary(in float increment);

};

class Manager extends Staff(extent managers)

{relationship Branch Manages inverse Branch::ManagedBy;

};

OODBMS25

Object Query Language -- OQL

A Query language for OODBMS.

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.

OODBMS26

OQL

SELECT [DISTINCT] <expression>

FROM <fromList>

[WHERE <expression>]

[GROUP BY <attribute1: expression1, attribute2, expression2, ..>]

[HAVING <predicate>]

[ORDER BY <expression>]

OODBMS27

OQL vs. SQL: A Simple Example

OODBMS28

select

c.fname, c.lname

from

Depts d, d.employs e,

e.hasChildren c

where

d.name = “Sales”

select

c.fname, c.lname

from

Depts d, Employee e,

Children c

where

d.name = “Sales” and

d.deptID = e.deptID and

c.parentID = e.empID

OQL SQL

Query: List the names of the children of employees working in the sales department.

OODBMS29

Find all branches in London:

SELECT b.branchNo

FROM branchOffices b

WHERE b.address.city = “London”;

This returns a type bag<string> but since branchNo is unique set<string>.

OQL: Extents

OODBMS30

Find the salaries of sales staff who work at the branches in London

SELECT DISTINCT s.salary

FROM BranchOffices b, b.WorksAt s

WHERE b.address.city = “London”;

This returns set<float>.

OQL: Traversal Paths

OODBMS31

Get structured set containing name, sex, and age for all staff who live in London:

SELECT struct (lName:s.name.lName, sex:s.sex, age:s.getAge())

FROM s IN Staff

WHERE s.WorksAt.address.city = “London”;

This returns bag<struct>.

OQL: Using Structures

OODBMS32

Get structured set containing name, sex, and age for all staff who live in London ordered by their salaries:

SELECT struct (lName:s.name.lName, sex:s.sex, age:s.getAge())

FROM s IN Staff

WHERE s.WorksAt.address.city = “London”

ORDER BY s.salary;

This returns a type list<struct>.

OQL: Order By

OODBMS33

How many staff work in branch number 003? 2 ways to query

SELECT COUNT(s) FROM s IN salesStaff

WHERE s.WorksAt.branchNo = “B003”;

COUNT(SELECT s FROM s IN salesStaff WHERE s.WorksAt.branchNo = “B003”);

Return staff who work in branches with more than 10 employees

SELECT s FROM s IN salesStaff WHERE COUNT(s.WorksAt) > 10;

COUNT can be used in any part of the OQL

OQL: Aggregates

OODBMS34

A type name constructor is used to create an object with identity:

Manager(staffNo: “SL21”, fName: “John”, lName: “White”,

address: “19 Taylor St, London”,

position: “Manager”, sex: “M”,

DOB: date“1945-10-01”, salary: 30000)

OQL: Creating Objects