Transcript CS263 - Computing - University of Surrey

OBJECT DATABASE SYSTEMS
PART ONE
 Advanced database application areas
 Problems associated with RDBMSs
 Third Generation DBMSs
 What is Object Orientation?
 What is an OODBMS?
DATABASES
ADVANCED APPLICATION AREAS
 Computer-Aided Design (CAD).
 Computer-Aided Manufacturing (CAM).
 Computer-Aided Software Engineering (CASE).
 Multimedia Systems.
 Digital Publishing.
 Geographic Information Systems (GIS).
 Scientific and Medical Systems.
RELATIONAL DBMSs
PROBLEMS
 Poor representation of ‘real world’ entities.
 Semantic overloading.
 Homogeneous data structure.
 Difficulty handling recursive queries.
 Impedance mismatch.
RELATIONAL DBMSs
PROBLEMS - REAL-WORLD OBJECTS
ER Diagram - Car
C#
CAR
Part of
W#
C#
WHEEL
Part of
T#
W#
TRIM
Has
Has
Part of
Has
S#
C#
SEAT
RELATIONAL DBMSs
PROBLEMS - REAL-WORLD OBJECTS
NORMALISATION
Car {C#, Chassis#, NoWheels, NoSeats, etc…}
Wheel {W#, C#, Size, Pressure, etc…}
Trim {T#, W#, Material, Cost, etc…}
Seat {S#, C#, Material, Size, Cost,, etc…}
To find out all details about a Car we would have to carry out a large
number of (expensive) JOIN operations.
Select *
From Car, Wheel, Trim, Seat
Where Car.C# = Wheel.C#
And Car.C# = Seat.C#
And Wheel.W# = Trim.W#;
RELATIONAL DBMSs
PROBLEMS - SEMANTIC OVERLOADING
ER Diagram
D#
Oversees
P#
D#
DOCTOR
Overseen by
PATIENT
D#
Kills
P#
DOCTOR
Killed by
D#
PATIENT
Doctor {D#, Name, Surgery, etc…}
Patient {P#, D#, Name, Address, DOB, etc…}
We do not record the
nature of the
relationship between
doctor and patient!
RELATIONAL DBMSs
PROBLEMS - HOMOGENEOUS DATA STRUCTURE
ACCOUNT TABLE
ACCOUNT
CUSTOMER BRANCH
200
324
345
350
400
456
JONES
GRAY
SMITH
GREEN
ONO
KHAN
STRATFORD
BARKING
STRATFORD
BARKING
BARKING
STRATFORD
BALANCE
1000.00
200.00
23.17
340.14
500.00
333.00
ALL ROWS HAVE THE SAME NUMBER OF ATTRIBUTES
ALL VALUES IN A COLUMN ARE OF THE SAME TYPE
ALL ATTRIBUTE VALUES ARE ATOMIC
RELATIONAL DBMSs
PROBLEMS - RECURSIVE QUERIES
Question - Who does SMITH work for?
Select E2.ENAME From EMP E1, EMP E2
Where E1.MGR = E2.EMPNO And E1.ENAME = “SMITH”;
?
KING
First Level Answer – SMITH works for FORD
Select E3.ENAME From EMP E1, EMP E2, EMP E3
Where E1.MGR = E2.EMPNO And E2.MGR = E3.EMPNO
And E1.ENAME = “SMITH”;
JONES
FORD
Second Level Answer - SMITH works for JONES
Select E4.ENAME From EMP E1, EMP E2, EMP E3, EMP E4
Where E1.MGR = E2.EMP And E2.MGR = E3.EMPNO
And E3.MGR = E4.EMPNO And E1.ENAME = “SMITH”;
Third Level Answer – SMITH works for KING
SMITH
RELATIONAL DBMSs
PROBLEMS - IMPEDANCE MISMATCH
SQL is a declarative, set-based language that is not
computationally complete!
Database applications require the use of a computationally
complete, record-based, procedural language such as C,
C++, Java, and PL/SQL.
We therefore have to map sets of data into records using
memory structures such as cursors.
This is expensive in terms of application processing time
and programming effort, accounting for around 30% of some
projects!
THIRD GENERATION DBMSs
MAIN AIMS
• Support Complex Active Objects
Allow both data and its associated behaviour to be
modelled to any level of complexity.
• Improve Extensibility
Allow for the dynamic extension of both allowable data
types and the behaviour associated with these types.
• Reduce the Impedance Mismatch
Ensure that there is a seamless integration between the
DBMS data model and that of the programming language
accessing the data.
Object Model
WHAT IS AN ATOMIC (LITERAL) OBJECT?
An atomic object is a container for a fixed value and serves the
same purpose as a constant in a programming language.
An atomic object cannot change its own state.
Examples of atomic types and atomic objects
Integer - e.g. 1, 2, 3, -5, -45, etc.....
Float - e.g. 1.52, -0.3456, 2.000, etc...
Boolean - i.e. True or False
Char - e.g. a, b, c, @, #, !, etc...
String - e.g. “Mark”, “Database Systems”
Object Model
WHAT IS A (MUTABLE) OBJECT?
UNIQUE OBJECT IDENTIFIER (OID)
I am an
object!
ATTRIBUTES
State
NAME MARK
DOB
14/02/1964
JOB
LECTURER
RELATIONSHIPS
BEHAVIOUR
Methods
CHANGE JOB
GET AGE
Object Model
WHAT IS A CLASS?
MARK
I am an
object!
I am also
an object!
IAN
Object Model
WHAT IS A CLASS?
PERSON CLASS
MARK
I am a
Person!
So am I!
PERSON
NAME
DOB
JOB
CHANGE JOB
GET AGE
IAN
Object Model
WHAT IS AN OBJECT IDENTIFIER (OID)?
Each object is uniquely identifiable from all other objects.
When an object is first created it is assigned a value to
identify it. This value is called its Object Identifier.
 System generated.
 Unique to that object.
 Invariant in that it cannot be altered.
 Independent of its attribute values.
 Invisible to the user.
Object Model
WHAT IS ENCAPSULATION?
GET AGE
CHANGE JOB
METHOD
NAME: MARK
DOB:
14/02/64
JOB:
LECTURER
GET AGE
METHOD
OBJECT
CHANGE JOB
Object Model
WHAT IS A COMPLEX OBJECT?
Is a Car a Complex Object?
Yes, it’s an object that is made up of other objects!
Wheels, Seats, Chassis, Exhaust, Steering Wheel, etc, etc...
And… a wheel itself is also a complex object!
Tire, Trim, Hub Cap, etc, etc...
Object Model
WHAT IS A COMPLEX OBJECT?
TIRE
TIRE
HUB
CAP
HUB
CAP
TRIM
WHEEL
SEAT
TIRE
HUB
CAP
TRIM
WHEEL
SEAT
REGISTRATION
NUMBER
WHEEL
CAR
SEAT
CHASSIS
WHEEL
SEAT
TRIM
TIRE
HUB
CAP
TRIM
Object Model
WHAT IS A COMPLEX OBJECT?
TIRE
A Wheel IS-PART-OF a Car
HUB
CAP
TRIM
WHEEL
SEAT
TIRE
HUB
CAP
TRIM
WHEEL
SEAT
REGISTRATION
NUMBER
TIRE
HUB
CAP
WHEEL
CAR
SEAT
CHASSIS
WHEEL
SEAT
A Car has a COLLECTION of Wheels
TRIM
TIRE
HUB
CAP
TRIM
Object Model
WHAT IS A COMPLEX OBJECT?
CAR
REG-NUMBER:
CHASSIS:
WHEELS:
SEATS:
WHEEL
TIRE:
STRING
WHEEL
HUB CAP: STRING
STRING
TIRE:
WHEEL
TRIM:
STRING
HUB
CAP: STRING
STRING
TIRE:
WHEEL
TRIM:
STRING
HUB
CAP:STRING
STRING
TIRE:
TRIM:
STRING
HUB
CAP: STRING
TRIM:
STRING
STRING
STRING
SET<WHEEL>
SET<SEAT>
SEAT
TIRE:
STRING
SEAT
HUB CAP: STRING
STRING
TIRE:
SEAT
TRIM:
STRING
HUB
CAP: STRING
STRING
TIRE:
SEAT
TRIM:
STRING
HUB
CAP:STRING
STRING
TYPE:
TRIM:
STRING
COLOUR:
STRING
POSITION: STRING
Object Model
WHAT IS A COLLECTION - SET?
SET - An unordered collection of
distinct objects of the same type
e.g, Customers : SET <Customer>;
BILL
An instance of
CUSTOMERS
MARK
HILDA
MARIE
CAROLINE
Object Model
WHAT IS A COLLECTION - BAG?
BAG - An unordered collection of
objects of the same type
e.g, Phone_calls : BAG <TelephoneNumber>;
555-9999
An instance of
PHONE_CALLS
444-3333
555-9999
111-3333
444-3333
Object Model
WHAT IS A COLLECTION - LIST?
LIST - An ordered collection of
objects of the same type
e.g, MachineFaults : LIST <Fault>;
Fault at 11:00:01
Fault at 11:00:20
An instance of
MachineFaults
Fault at 11:31:00
Fault at 11:44:33
Fault at 12:00:00
Object Model
WHAT IS A COLLECTION - ARRAY?
ARRAY – Each object is stored at a particular position
e.g, StudySchedule : ARRAY <Task>;
An instance of StudySchedule
0
1
2
3
4
5
6
7
8
9
10 11
12 13
Object Model
WHAT IS A STRUCTURE?
A fixed number of named slots, each of which can contain an
object of a particular type.
e.g, CustomersDetails : STRUCTURE <
forenames : List < String>,
family_name : String,
customer_no : Integer >
Marie
An instance of
CustomerDetails
Rebecca
Campbell
9603456
family_name
customer_no
Caroline
forenames
Object Model
WHAT IS INHERITANCE?
IS-A
Person
name
address
telephone_no
change_name (...)
change_address (...)
Employee
employee_no
promote(...)
pay_employee (...)
IS-A
Customer
customer_no
place_order(...)
make_payment(...)
IS-A
TradeCustomer
trade_discount%
place_order(...)
make_payment(...)
Object Model
WHAT IS MULTIPLE INHERITANCE?
Person
name
address
telephone_no
change_name (...)
change_address (...)
Employee
employee_no
promote(...)
pay_employee (...)
Customer
customer_no
place_order(...)
make_payment(...)
IS-A
IS-A
Employee_Customer
staff_discount_card
place_order(...)
make_payment(...)
TradeCustomer
trade_discount%
place_order(...)
make_payment(...)
Object Model
WHAT ARE OBJECT RELATIONSHIPS?
Husband
....
....
1
husband_of
wife_of
1
Wife
....
....
one-to-one
Child
....
....
*
child_of
1
mother_of
Mother
....
....
one-to-many
Child
....
....
*
child_of
parent_of
*
many-to-many
Parent
....
....
Object Model
WHAT ARE METHODS AND MESSAGES?
NAME: MARK
DOB:
14/02/64
JOB:
LECTURER
CHANGE JOB
METHOD
BODY
DISK
GET AGE
METHOD
BODY
OBJECT
Object Model
WHAT IS POLYMORPHISM?
ANALOGUE
CLOCK
...
CLOCK
...
SetTime ()
SetAlarm ()
ShowTime ()
SetTime ()
SetAlarm ()
ShowTime ()
DIGITAL
CLOCK
...
SetTime ()
SetAlarm ()
ShowTime ()
DIFFERENT TYPES OF
OBJECT RESPOND
DIFFERENTLY TO THE
SAME MESSAGE
11:00
PM
Object Model
WHAT IS OVERIDING?
When a sub-class’s method body is used rather than the body
of the super-class’s method it is known as overriding.
CUSTOMER
Customer No.
PlaceOrder()
MakePayment()
METHOD BODY
1. Create order details
2. Calculate total cost
IS-A
TRADE
CUSTOMER
TradeDiscount%
PlaceOrder()
METHOD BODY
1. Create order details
2. Calculate total cost
3. Apply Trade Discount
Object Model
WHAT IS LATE BINDING?
Late or dynamic binding is the ability of the runtime system
to determine which method body to execute depending on the
type of an object.
Customers := SET <Customer>
CUSTOMER
TIRE: Customer
STRING
Trade
HUB CAP: STRING
STRING
TIRE:
CUSTOMER
TRIM:
STRING
HUB
CAP: STRING
TIRE:
Trade
Customer
TRIM:
STRING
HUB
CAP: NO
CUSTOMER
TRIM:
STRIN
PLACE_ORDER
MAKE_PAYMENT
FOR x IN Customers
DO
x.PLACE_ORDER
END
Where x := an individual
Customer Object!
It doesn’t matter if a customer is a trade customer, late binding
ensures the appropriate PLACE_ORDER method body is called!
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.
OBJECT ORIENTED DATABASE MANAGEMENT SYSTEM
OOPLs
DBMSs
Complex Objects
Object Identity
Methods & Messages
Inheritance
Polymorphism
Extensibility
Computational Completeness
Persistence
Disc Management
Data Sharing
Reliability
Security
Ad Hoc Querying
OODBMS
WHAT AN OODBMS SHOULD SUPPORT?







Atomic and complex objects
Methods and messages
Object Identity
Single inheritance
Polymorphism - overloading and late-binding
Persistence
Shared Objects
In addition an OODBMS can optionally support




Multiple inheritance
Exception messages
Distribution
Versioning
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
OODBMSs
REQUIREMENTS AND FEATURES
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.
TWO-LEVEL STORAGE MODEL FOR A RDBMS
Main or virtual
memory
Transforming and
type checking
SQL
Secondary
storage
ACCESSING A RECORD USING AN RDBMS
Page
3. Access object
Record
4. Copy modified fields
2. Copy relevant fields
Page
Record
5. Save page
1. Read page
Page
Record
SINGLE-LEVEL STORAGE MODEL
FOR AN OODBMS
Main or virtual
memory
Secondary
storage
ACCESSING AN OBJECT USING AN OODBMS
3. Access object
Page
4. Swizzle pointers
back, etc.
Object
5. Save page
2. Swizzle
pointers, etc.
1. Read page
Page
Object
OODBMSs
ADVANTAGES
 Enriched modelling capabilities
 Extensibility
 Removal of Impedance Mismatch
 Support for schema evolution.
 Applicable for advanced database applications
 Improved performance.
OODBMSs
DISADVANTAGES
 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
ORDBMSs
WHAT IS AN ORDBMS?
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.
In essence ORDBMSs are an attempt
to add OO to Tables!
ORDBMSs
MAJOR DIFFERENCE BETWEEN AN
ORDBMS AND AN OODBMS
OODBMSs try to add DBMS functionality to one
or more OO programming languages.
REVOLUTIONARY IN THAT THEY ABANDON SQL
ORDBMSs try to add richer data types and OO
features to a relational DBMS.
EVOLUTIONARY IN THAT THEY EXTEND SQL
ORDBMSs
WHAT IS SQL3?
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!
ORDBMSs
WHAT IS NEW IN SQL3?
 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.
ORDBMSs
SQL3 - EXTENDED BASE TYPES
ONE OF THE REASONS FOR THE MOVE AWAY
FROM 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, ...
ORDBMSs
SQL3 - ROW TYPES
BRANCHNO
10
20
30
ADDRESS
STREET
AREA
CITY
MAIN ST.
HIGH RD.
HIGH ST.
BARKING
LEYTON
MARSDEN
LONDON
LONDON
OXFORD
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!
ORDBMSs
SQL3 - USER-DEFINED TYPES
CREATE TYPE person_type AS (
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)
ORDBMSs
SQL3 - SUB-TYPES & SUPER-TYPES
PERSON-TYPE
date of birth
name
address
tel-no
get_age()
Sub-Types and Super-Types are used to
allow for INHERITANCE in SQL3
A Sub-Type can inherit from more than
one Super-Type.
Multiple Inheritance is allowed!
STAFF-TYPE
sno
position
salary
branch
is_manager()
ORDBMSs
SQL3 - SUB-TYPES & SUPER-TYPES
CREATE TYPE staff_type UNDER person_type AS (
sno
position
salary
bno
VARCHAR(5) NOT NULL UNIQUE,
VARCHAR(10) NOT NULL,
NUMBER(7,2),
VARCHAR(3) NOT NULL,
CREATE FUNCTION is_manager (s STAFF_TYPE)
RETURNS BOOLEAN
BEGIN
IF s.position = ‘Manager’ THEN
RETURN TRUE;
ELSE
RETURN FALSE;
END IF
END)
NOT FINAL;
Another example of a User-Defined Routine (UDR)
ORDBMSs
SQL3 - TYPES & TABLES
In order to remain upwardly compatible with SQL-92,
TYPES can ONLY be 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!
EXAMPLE:
In order to create staff instances we first have to do one of the following:
CREATE TABLE staff OF STAFF_TYPE (
PRIMARY KEY sno);
CREATE TABLE staff (
info
STAFF_TYPE,
PRIMARY KEY sno);
ORDBMSs
SQL3 - SUB-TABLES & SUPER-TABLES
PROBLEM - What happens if we create two or more tables
for the same TYPE? How do we find all TYPE instances?
EXAMPLE: FIND ALL MEMBERS OF STAFF!
CREATE TABLE lecturer OF STAFF_TYPE (
PRIMARY KEY sno);
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!
ORDBMSs
SQL3 - SUB-TABLES & SUPER-TABLES
SUPER-TABLE
CREATE TABLE staff OF STAFF_TYPE (
PRIMARY KEY sno);
SUB-TABLES
CREATE TABLE lecturer OF STAFF_TYPE UNDER staff (
PRIMARY KEY sno);
CREATE TABLE admin OF STAFF_TYPE UNDER staff (
PRIMARY KEY sno);
SOLUTION TO PROBLEM (FIND ALL STAFF):
SQL> SELECT * FROM staff;
ORDBMSs
SQL3 - REFERENCE TYPES AND OIDS
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!
EXAMPLE:
CREATE TYPE staff_type UNDER person_type AS (
sno
VARCHAR(5) NOT NULL UNIQUE,
position VARCHAR(10) NOT NULL,
salary
NUMBER(7,2),
Could point to a row in ANY
next_of_kin REF(person_type)
table containing a person_type!
bno
VARCHAR(3) NOT NULL)
NOT FINAL;
CREATE TABLE person OF person_type (
oid
REF(person_type) VALUES ARE SYSTEM GENERATED);
ORDBMSs
SQL3 - REFERENCE TYPES AND OIDS
To ensure that a REFERENCE is limited to a single table, a SCOPE
has to be added to the table using the REFERENCE!
EXAMPLE:
CREATE TYPE staff_type UNDER person_type AS (
sno
VARCHAR(5) NOT NULL UNIQUE,
position VARCHAR(10) NOT NULL,
salary
NUMBER(7,2),
staff next_of_kin will point
next_of_kin REF(person_type)
to a row in the person table!)
bno
VARCHAR(3) NOT NULL)
NOT FINAL;
CREATE TABLE person OF person_type (
oid
REF(person_type) VALUES ARE SYSTEM GENERATED);
CREATE TABLE staff OF staff_type (
PRIMARY KEY sno,
SCOPE FOR next_of_kin IS person);
ORDBMSs
SQL3 - COLLECTION TYPES
SQL3 COLLECTION TYPES ARE THE EQUIVALENT
OF COLLECTION TYPES IN OODBMSs
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
KNOWN AS A ‘BAG’ IN AN OODBMS!
ORDBMSs
SQL3 - COLLECTION TYPES
EXAMPLE
CREATE TABLE branch (
bno
NUMBER(3),
address ROW ( street
VARCHAR(15),
area
VARCHAR(15),
city
VARCHAR(15)
staff
SET (STAFF_TYPE));
THE USE OF COLLECTION TYPES WITHIN
TABLES ENSURE THAT TABLES NO LONGER
HAVE TO BE IN 1NF
REPEATING GROUPS ARE ALLOWED!
ORDBMSs
SQL3 - OTHER ADDITIONS
THE MAIN ADDITIONS TO SQL THAT ARE NOT
SPECIFICALLY ASSOCIATED WITH ADDING
OBJECT-SUPPORT ARE THE FOLLOWING:
SQL IS NOW COMPUTATIONALLY COMPLETE
PERSISTENT STORED MODULES ARE SUPPORTED
TRIGGERS ARE SUPPORTED
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 query – Still have Impedance Mismatch!
OODBMSs have been optimised to directly support objectoriented applications and specific OO languages.
ORDBMSs are supported by most of the ‘major players’ in the
DBMS market place.
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.
OODBMS – The ODMG standard group’s 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
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).
OODBMS or ORDBMS
WHEN TO USE AN OODBMS
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 of
concurrency control.
OODBMS or ORDBMS
WHEN TO USE AN ORDBMS
In applications that process a large number of shortlived (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 traditional
concurrency control is acceptable.