oodbms&ordbms

8/13/2019 OODBMS&ORDBMS

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Object (and Object-Relational)

Database Systems (part two)CSS263 Lecture 18


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LECTURE PLAN

OBJECT DATABASE SYSTEMS

PART TWO

What is an OODBMS?

Advantages and Disadvantages of OODBMSs

What is an ORDBMS?

What is SQL3?

Comparison of OODBMSs and ORDBMSs

When to use an OODBMS

When to use an ORDBMS


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REMINDER OF THE PROBLEMS

ASSOCIATED WITH AN RDBMS


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RELATIONAL DBMSs

Poor representation of real world entities.

Semantic overloading.

Poor support for integrity and business constraints.

Homogeneous data structure.

Limited operations.

Difficulty handling recursive queries.

Impedance mismatch.

Difficulty with Long Transactions.

PROBLEMS


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WHAT IS AN OODBMS?


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OODBMS


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OODBMS

WHAT IS AN OODBMS?

Object Oriented Database Management Systems (OODBMSs) are an attempt

at marrying the power of Object Oriented Programming Languages with the

persistence and associated technologies of a DBMS.

OOPLs DBMSs

Complex Objects Persistence

Object Identity Disc Management

Methods & Messages Data Sharing

Inheritance ReliabilityPolymorphism Security

Extensibility Ad Hoc Querying

Computational Completeness

OBJECT ORIENTED DATABASE MANAGEMENT SYSTEM


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REQUIREMENTS AND FEATURES

OODBMSs

Requirements:

Transparently add persistence to OO programming languages

Ability to handle complex data - i.e., Multimedia data

Ability to handle data complexity - i.e., Interrelated data items

Add DBMS Features to OO programming languages

Features:

The host programming language is also the DML.

The in-memory and storage models are merged.

No conversion code between models and languages is needed.


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TWO-LEVEL STORAGE MODEL FOR A RDBMS

SQL

Transforming and

type checking

Main or virtualmemory

Secondary

storage


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Record

Record

Record

3. Access object

4. Copy modified fields 2. Copy relevant fields

5. Save page 1. Read page

Page

Page

Page

ACCESSING A RECORD USING AN RDBMS


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Main or virtual

memory

Secondary

storage

SINGLE-LEVEL STORAGE MODEL

FOR AN OODBMS


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3. Access object

5. Save page 1. Read page

Page

Page

Object

Object

4. Swizzle pointers

back, etc.

2. Swizzle

pointers, etc.

ACCESSING AN OBJECT USING AN OODBMS


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ADVANTAGES AND DISADVANTAGES OF

AN OODBMS?


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ADVANTAGES

OODBMSs

Enriched modelling capabilities

Extensibility

Removal of Impedance Mismatch

Support for schema evolution.

Support for long duration transactions.

Applicable for advanced database applications

Improved performance.


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DISADVANTAGES

OODBMSs

Lack of a universal data model

Lack of experience

Lack of standards.

Ad-hoc querying compromises encapsulation.

Locking at object-level impacts performance

Complexity

Lack of support for views

Lack of support for security


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WHAT IS AN ORDBMS?

In essence ORDBMSs are an attempt

to add OO to Tables!

ORDBMSs

Definition:

Object-Relational databases extend the Relational Data Model

to address those weaknesses identified previously.

An Object-Relational database adds features associated with

object-oriented systems to the Relational Data Model.


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MAJOR DIFFERENCE BETWEEN AN

ORDBMS AND AN OODBMS

OODBMSs try to add DBMS functionality to one

or more OO programming languages.

ORDBMSs

REVOLUTIONARYIN THAT THEY ABANDON SQL

ORDBMSs try to add richer data types and OO

features to a relational DBMS.

EVOLUTIONARYIN THAT THEY EXTEND SQL


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SQL3


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WHAT IS SQL3?

ORDBMSs

SQL3 or SQL/99:

SQL3 is a superset of SQL/92, in that it supports all

of the constructs supported by that standard, as well

as adding new ones of its own.

Therefore, whatever worked in an implementation of

SQL/92 should also work in an implementation of

SQL3.HOWEVER, IT SHOULD BE NOTED THAT AS YET

THERE ARE NO IMPLEMENTATIONS OF SQL3!


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WHAT IS NEW IN SQL3?

ORDBMSs

Extended Base Types.

Row Types.

User-Defined Types.

User-Defined Routines.

Sub-Types and Super-Types.

Sub-Tables and Super-Tables.

Reference Types and Object Identity.

Collection Types.


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SQL3 - EXTENDED BASE TYPES

ORDBMSs

ONE OF THE REASONS FOR THE MOVE AWAYFROM RDBMSs IS THE LIMITED BASE TYPE

AVAILABILITY:

BASE TYPES AVAILABLE IN SQL/92 INCLUDE:

NUMBER, CHAR, DATE, ...

BASE TYPES IN SQL3 ARE EXTENSIBLE. THEREFORE THE

FOLLOWING MUCH NEEDED TYPES COULD BE ADDED

(PROVIDED SOMEBODY CREATES THEM!)

VIDEO, IMAGE, AUDIO, TEXT, SPATIAL, TEMPORAL,

GEOGRAPHIC, WEB-PAGES, ...

O S


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SQL3 - ROW TYPES

ORDBMSs

CITYAREASTREET

ADDRESS

OXFORDMARSDENHIGH ST.30

LONDONLEYTONHIGH RD.20

LONDONBARKINGMAIN ST.10

BRANCHNO

CREATE TABLE branch(

branchno VARCHAR(3),address ROW( street VARCHAR(25),

area VARCHAR(15),

city VARCHAR(15));

COLUMN ATTRIBUTES NO LONGER HAVE TO BE ATOMIC!

ORDBMS


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SQL3 - USER-DEFINED TYPES

ORDBMSs

CREATE TYPE person_typeAS (PRIVATE

date_of_birth DATE

CHECK (date_of_birth > DATE 1900-01-1901),

PUBLIC

name VARCHAR(15) NOT NULL,address VARCHAR(50) NOT NULL,

tel_no VARCHAR(13) NOT NULL,

FUNCTION get_age(P person_type)

RETURNS INTEGER

/* code to calculate age from date_of_birth */RETURN

END)

NOT FINAL;

An example of a User-Defined Routine (UDR)

ORDBMS


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SQL3 - SUB-TYPES & SUPER-TYPES

ORDBMSs

PERSON-TYPE

date of birth

name

address

tel-no

get_age()

STAFF-TYPE

snoposition

salary

branch

is_manager()

Sub-Types and Super-Types are used to

allow for INHERITANCEin SQL3

A Sub-Type can inherit from more thanone Super-Type.

Multiple Inheritance is allowed!


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ORDBMS


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SQL3 - TYPES & TABLES

ORDBMSs

In order to remain upwardly compatible with SQL-92,

TYPES can ONLYbe instantiated through SQL Tables!

Therefore, in order to create instances of a type we first have

to create a table to store those instances in!

CREATE TABLE staff OF STAFF_TYPE (

PRIMARY KEY sno);

EXAMPLE:

In order to create staff instances we first have to do one of the following:

CREATE TABLE staff (

info STAFF_TYPE,

PRIMARY KEY sno);

ORDBMS


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SQL3 - SUB-TABLES & SUPER-TABLES

ORDBMSs

PROBLEM - What happens if we create two or more tables

for the same TYPE? How do we find all TYPE instances?

CREATE TABLE lecturer OF STAFF_TYPE (PRIMARY KEY sno);

EXAMPLE: FIND ALL MEMBERS OF STAFF!

CREATE TABLE admin OF STAFF_TYPE (

PRIMARY KEY sno);

The only way of doing this is to declare the lecturer and

admin tables as sub-tables of a staff super-table!

ORDBMS


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SQL3 - SUB-TABLES & SUPER-TABLES

ORDBMSs

CREATE TABLE lecturer OF STAFF_TYPE UNDERstaff(

PRIMARY KEY sno);

CREATE TABLE admin OF STAFF_TYPE UNDERstaff(

PRIMARY KEY sno);

CREATE TABLE staff OF STAFF_TYPE (

PRIMARY KEY sno);

SUPER-TABLE

SUB-TABLES

SOLUTION TO PROBLEM (FIND ALL STAFF):

SQL>SELECT * FROM staff;

ORDBMS


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SQL3 - REFERENCE TYPES AND OIDS

ORDBMSs

A Reference Type is the SQL3 equivalent of an OID in an OODBMS.

Reference Types allow a row to be shared among multiple tables, and

enable users to replace complex join operations with path expressions!

CREATE TYPE staff_typeUNDER person_typeAS (

sno VARCHAR(5) NOT NULL UNIQUE,

position VARCHAR(10) NOT NULL,

salary NUMBER(7,2),

next_of_kin REF(person_type)

bno VARCHAR(3) NOT NULL)

NOT FINAL;

CREATE TABLE person OF person_type(

oid REF(person_type) VALUES ARE SYSTEM GENERATED);

EXAMPLE:

Could point to a row in ANY

table containing a person_type!

ORDBMS


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SQL3 - REFERENCE TYPES AND OIDS

ORDBMSs

To ensure that a REFERENCE is limited to a single table, a SCOPEhas to be added to the table using the REFERENCE!

CREATE TYPE staff_typeUNDER person_typeAS (

sno VARCHAR(5) NOT NULL UNIQUE,

position VARCHAR(10) NOT NULL,

salary NUMBER(7,2),

next_of_kin REF(person_type)

bno VARCHAR(3) NOT NULL)

NOT FINAL;

CREATE TABLE person OF person_type(

oid REF(person_type) VALUES ARE SYSTEM GENERATED);

EXAMPLE:

CREATE TABLE staff OF staff_type(

PRIMARY KEY sno,

SCOPEFOR next_of_kin IS person);

staff next_of_kinwill point

to a row in the person table!)

ORDBMS


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SQL3 - COLLECTION TYPES

ORDBMSs

List(base) - ordered collection allows duplicates

Array(base) - one-dimensional array, max no.

Set(base) - unordered collection, no duplicates

Multiset(base) - unordered collection, allows duplicates

SQL3 COLLECTION TYPES ARE THE EQUIVALENTOF COLLECTION TYPES IN OODBMSs

KNOWN AS A BAG IN AN OODBMS!

ORDBMS


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SQL3 - COLLECTION TYPES

ORDBMSs

CREATE TABLE branch (

bno NUMBER(3),

address ROW ( street VARCHAR(15),

area VARCHAR(15),

city VARCHAR(15)

staff SET (STAFF_TYPE));

EXAMPLE

THE USE OF COLLECTION TYPES WITHIN

TABLES ENSURE THAT TABLES NO LONGER

HAVE TO BE IN 1NF

REPEATING GROUPS ARE ALLOWED!

ORDBMSs


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SQL3 - OTHER ADDITIONS

ORDBMSs

THE MAIN ADDITIONS TO SQL THAT ARE NOTSPECIFICALLY ASSOCIATED WITH ADDING

OBJECT-SUPPORT ARE THE FOLLOWING:

SQL IS NOW COMPUTATIONALLY COMPLETEPERSISTENT STORED MODULES ARE SUPPORTED

TRIGGERS ARE SUPPORTED


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OODBMS or ORDBMS?

OODBMS or ORDBMS


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OODBMS or ORDBMS

CONSIDERATIONS

OODBMS- put more emphasis on the role of the client, i.e.,

Client side caching! This can radically improve long, process

intensive, transactions.

ORDBMS- SQL is still the language for data definition,manipulation and queryStill have Impedance Mismatch!

OODBMSshave been optimised to directly support object-

oriented applications and specific OO languages.

ORDBMSsare supported by most of the major players in the

DBMS market place.

OODBMS or ORDBMS


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OODBMS or ORDBMS

CONSIDERATIONS

ORDBMS- Most third-party database tools are written for

the relational model (SQL-92), and will therefore be

backward-compatible with SQL3.

ORDBMS- search, access and manipulate complex data types

in the database with standard SQL (SQL3), without breaking

the rules of the relational data model.

OODBMSThe ODMG standard groups OQL is now the

de-facto query language amongst OODBMS vendors.However, in order to use it, collection objects (known as

extents) have to first be created for each class.

OODBMS or ORDBMS


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OODBMS or ORDBMS

CONSIDERATIONS

OODBMS- In order to realise the value of an OODBMS you

must build your application using methods written in one of

several object-oriented language (i.e. C++, Java, Smalltalk).


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WHEN TO USE AN OODBMS

OODBMS or ORDBMS


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WHEN TO USE AN OODBMS

OODBMS or ORDBMS

In applications that generally retrieve relatively few(generally physically large) highly complex objects

and work on them for fairly long periods of time.

This will necessitate the use of client caching,

pointer swizzling, and non-locking forms ofconcurrency control.


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WHEN TO USE AN ORDBMS

OODBMS or ORDBMS


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WHEN TO USE AN ORDBMS

OODBMS or ORDBMS

In applications that process a large number of short-lived (generally ad-hoc query) transactions on data

items that can be arbitrarily complex in structure.

Where the main emphasises is on efficient query

optimisation to limit disk accesses, and traditionalconcurrency control is acceptable.

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