Object-Relational Database Slides

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Object-RelationalDatabase



Relational Strengths and Weaknesses� Strengths

± Data independence

± Powerful query language

± Well-developed backup and recovery,

concurrency control, etc.� Weaknesses

± Support for complex data types

±

Support for generalization/specialization ± Encapsulation



Object-Relational DBMS (ORDBMS)� Supports relational and object-

oriented features

� Query relations and objects through

a single query language

� ³Extended Relational DBMS´

� ³Universal DBMS´



Features of an ORDBMS� Enhanced SQL to work with both relations

and objects

� Support for:

± Generalization/specialization

± Inheritance

± Polymorphism

± Additional, defined data types, e.g. BLOBs

± User-defined or abstract data types

±

Storage of code in the database ± Aggregation

± Object identifiers (OIDs)

± Multivalued attributes



5

User-Defined Data Type� CREATE NAME_TYPE

AS OBJECT(

LASTNAME VARCHAR2(25)

FIRSTNAME VARCHAR2(25)

MIDDLEINIT CHAR(1));



6

User-Defined Data Type� CREATE PERSON_TYPE

AS OBJECT(

NAME NAME_TYPE,

ADDRESS ADDRESS_TYPE,

DATEBIRTH DATE,

PHONE VARCHAR2(12));



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User-Defined Data Type� CREATE TABLE EMPLOYEE(

EMPID NUMBER(8) NOT NULL

PRIMARY KEY

EMP PERSON_TYPE);



8

Generalization/Specialization� CREATE TYPE EMP_TYPE

AS OBJECT(

EMPNO NUMBER,

EMPNAME VARCHAR2(50)

EMPADDRESS VARCHAR2(100))NOT FINAL;

CREATE TYPE HOURLY_EMP_TYPE

UNDER EMP_TYPE(HOURLYRATE NUMBER);

CREATE TABLE HOURLY_EMP

OF HOURLY_EMP_TYPE;



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Content Addressing� Consider an employee table with a

field for each employee¶s photo,defined as

EMP_PHOTO IMAGE

� SELECT *

FROM EMPLOYEE

WHERE MY_PHOTO LIKE

EMP_PHOTO;



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Encapsulation� CREATE TYPE ADDR_TYPE AS(

STREET VARCHAR(45),CITY VARCHAR(25),

ZIP CHAR(5))

METHOD APT_NO() RETURNS

CHAR(8);

� METHOD

CREATE FUNCTION APT_NO()

RETURNS CHAR(8) FORADDR_TYPE AS

EXTERNAL NAME µ/X/Y/APTNO.CLASS¶

LANGUAGE µJAVA¶;



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ORDBMS Vendors and Products� IBM ± DB2 Universal Database

� Informix ± Dynamic Server

� Oracle ± Oracle 10g

� PostgreSQL Inc. ± PostgreSQL

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