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Transcript 
Object-Relational Databases
Database
Management
Peter Wood
Object-Relational
Databases
User-Defined Types
Type Inheritance
Table Inheritance
Why is the relational model so successful?
I
Data independence
I
High level query language - SQL
I
Query optimisation
I
Support for integrity constraints
I
Well-understood database design
I
Transaction management and concurrency
Array and Multiset Types
Object Identity and
References
Why might we need Object-Oriented
Databases?
Database
Management
Peter Wood
Object-Relational
Databases
User-Defined Types
Type Inheritance
Table Inheritance
Array and Multiset Types
I
For some applications 1NF is too strict.
I
I
I
I
Document management and web site management
Geographic and Statistical database management
Biological data management
SQL is not a complete programming language such
as C++ and Java — early versions did not support
abstract data types
Object Identity and
References
Object-Oriented Approach
Database
Management
Peter Wood
Object-Relational
Databases
User-Defined Types
I
Couple an Object-Oriented programming language
with a DBMS
I
One approach is to implement on top of a relational
DBMS.
I
Object-Oriented databases failed to deliver robust
and versatile systems which can compete with
relational database technology
I
Object-Relational approach — integrate
Object-Oriented features into existing relational
DBMSs
Type Inheritance
Table Inheritance
Array and Multiset Types
Object Identity and
References
Object-Relational Databases
Database
Management
Peter Wood
Object-Relational
Databases
Object-relational systems (and SQL:1999) provide a
number of extra features over relational systems,
including:
I
user-defined types
I
type inheritance
I
table inheritance
I
array and multiset types
I
object identity
I
reference types
I
methods
User-Defined Types
Type Inheritance
Table Inheritance
Array and Multiset Types
Object Identity and
References
Creating User-Defined Types
Database
Management
Peter Wood
Object-Relational
Databases
CREATE TYPE NameType AS (
firstname
varchar(20),
lastname
varchar(20))
FINAL;
CREATE TYPE AddressType AS (
street
varchar(20),
city
varchar(20)
postcode
varchar(8))
NOT FINAL;
FINAL and NOT FINAL relate to subtyping (see later)
User-Defined Types
Type Inheritance
Table Inheritance
Array and Multiset Types
Object Identity and
References
Using User-Defined Types
Database
Management
Peter Wood
Object-Relational
Databases
User-Defined Types
CREATE TABLE person (
name
NameType,
address
AddressType,
dateOfBirth date);
Note that the above table definition uses the user-defined
types NameType and AddressType, along with the built-in
type date
Type Inheritance
Table Inheritance
Array and Multiset Types
Object Identity and
References
Using User-Defined Types
Database
Management
Peter Wood
Object-Relational
Databases
User-Defined Types
CREATE TABLE person (
name
NameType,
address
AddressType,
dateOfBirth date);
Note that the above table definition uses the user-defined
types NameType and AddressType, along with the built-in
type date
An SQL example using the above definition is:
SELECT name.firstname, name.lastname FROM person;
Type Inheritance
Table Inheritance
Array and Multiset Types
Object Identity and
References
Type Inheritance
Database
Management
Peter Wood
CREATE TYPE PersonType (
name
Name,
address
Address)
NOT FINAL;
CREATE TYPE StudentType UNDER PersonType (
degree
varchar(20),
department varchar(20))
FINAL;
StudentType is a subtype of PersonType.
NOT FINAL means the type can have subtypes.
FINAL means the type cannot have subtypes.
StudentType inherits the attributes of PersonType.
Object-Relational
Databases
User-Defined Types
Type Inheritance
Table Inheritance
Array and Multiset Types
Object Identity and
References
Table Inheritance
Database
Management
Peter Wood
Object-Relational
Databases
User-Defined Types
Type Inheritance
CREATE TABLE person OF PersonType;
Table Inheritance
Array and Multiset Types
Object Identity and
References
CREATE TABLE student OF StudentType UNDER person;
Table student will have all attributes of StudentType
(which includes those of PersonType).
Table Inheritance
Database
Management
Peter Wood
Object-Relational
Databases
User-Defined Types
Type Inheritance
CREATE TABLE person OF PersonType;
Table Inheritance
Array and Multiset Types
Object Identity and
References
CREATE TABLE student OF StudentType UNDER person;
Table student will have all attributes of StudentType
(which includes those of PersonType).
Every tuple in student is implicitly also in person, so
SELECT * FROM person
retrieves all person tuples, including student tuples.
Array and Multiset Types
Multiset (a set with possibly duplicate elements) types
were added in SQL:2003.
Database
Management
Peter Wood
Object-Relational
Databases
User-Defined Types
CREATE TYPE Book AS (
title
varchar(20),
authors
varchar(20) array [10],
keywords
varchar(20) multiset)
NOT FINAL;
CREATE TABLE books OF Book;
Type Inheritance
Table Inheritance
Array and Multiset Types
Object Identity and
References
Array and Multiset Types
Multiset (a set with possibly duplicate elements) types
were added in SQL:2003.
Database
Management
Peter Wood
Object-Relational
Databases
User-Defined Types
CREATE TYPE Book AS (
title
varchar(20),
authors
varchar(20) array [10],
keywords
varchar(20) multiset)
NOT FINAL;
CREATE TABLE books OF Book;
INSERT INTO books
VALUES (’Database System Concepts’,
array[’Silberschatz’, ’Korth’, ’Sudarshan’],
multiset[’computer’, ’database’, ’SQL’]);
Type Inheritance
Table Inheritance
Array and Multiset Types
Object Identity and
References
Array and Multiset Types
Multiset (a set with possibly duplicate elements) types
were added in SQL:2003.
Database
Management
Peter Wood
Object-Relational
Databases
User-Defined Types
CREATE TYPE Book AS (
title
varchar(20),
authors
varchar(20) array [10],
keywords
varchar(20) multiset)
NOT FINAL;
CREATE TABLE books OF Book;
INSERT INTO books
VALUES (’Database System Concepts’,
array[’Silberschatz’, ’Korth’, ’Sudarshan’],
multiset[’computer’, ’database’, ’SQL’]);
SELECT authors[1] FROM books
WHERE ’database’ IN (UNNEST(keywords));
Type Inheritance
Table Inheritance
Array and Multiset Types
Object Identity and
References
Object Identity and References
Database
Management
Peter Wood
Tuples in a table can be declared to have identifiers
(using REF IS).
Object-Relational
Databases
User-Defined Types
This allows for data sharing (using REF) without
duplication, e.g. a couple having the same children
CREATE TABLE person OF PersonType (
REF IS personID SYSTEM GENERATED);
CREATE TABLE Department (
name
varchar(20),
head
REF(PersonType) SCOPE person);
The reference is restricted to tuples of the table person.
Makes references behave like foreign keys.
Type Inheritance
Table Inheritance
Array and Multiset Types
Object Identity and
References
Object Identity and References
Database
Management
Peter Wood
Tuples in a table can be declared to have identifiers
(using REF IS).
Object-Relational
Databases
User-Defined Types
This allows for data sharing (using REF) without
duplication, e.g. a couple having the same children
CREATE TABLE person OF PersonType (
REF IS personID SYSTEM GENERATED);
CREATE TABLE Department (
name
varchar(20),
head
REF(PersonType) SCOPE person);
The reference is restricted to tuples of the table person.
Makes references behave like foreign keys.
SELECT name, deref(head).name FROM Department;
Type Inheritance
Table Inheritance
Array and Multiset Types
Object Identity and
References
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