Object (and Object-Relational) Database Systems (part two)

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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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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
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CHARACTERISTICS THAT MUST BE SUPPORTED
     Complex objects      Object Identity
     Encapsulation      Classes     
Inheritance      Overriding and
late-binding      Extensibility     
Computational completeness     
Persistence      Concurrency     
Recovery      Ad-hoc querying  
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• 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.

REQUIREMENTS AND FEATURES
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TWO-LEVEL STORAGE MODEL FOR A RDBMS
Main or virtual
memory
Transforming and
type checking
SQL
Secondary
storage
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ACCESSING A RECORD USING AN RDBMS
Page
Application memory
Record
Page
DBMS Cache
Record
Page
Secondary Storage
Record
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SINGLE-LEVEL STORAGE MODEL FOR AN OODBMS
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ACCESSING AN OBJECT USING AN OODBMS
Page
3. Access object
2. Swizzle pointers, etc.
Application memory
4. Swizzle pointers back, etc.
Object
5. Save page
1. Read page
Page
Secondary Storage
Object
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ADVANTAGES AND DISADVANTAGES OF AN OODBMS?
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• 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.

ADVANTAGES
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• 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

DISADVANTAGES
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WHAT IS AN ORDBMS?
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• 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.

WHAT IS AN ORDBMS?
In essence ORDBMSs are an attempt to add OO to
Tables!
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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
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SQL3
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• 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.

WHAT IS SQL3?
HOWEVER, IT SHOULD BE NOTED THAT AS YET THERE ARE
NO IMPLEMENTATIONS OF SQL3!
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• 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.

WHAT IS NEW IN SQL3?
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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, ...
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ORDBMSs
SQL3 - ROW TYPES
COLUMN ATTRIBUTES NO LONGER HAVE TO BE ATOMIC!
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ORDBMSs
SQL3 - USER-DEFINED TYPES
CREATE TYPE person_type AS ( PRIVATE date_of_bi
rth DATE CHECK (date_of_birth gt 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
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ORDBMSs
SQL3 - SUB-TYPES SUPER-TYPES
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!
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ORDBMSs
SQL3 - SUB-TYPES SUPER-TYPES
CREATE TYPE staff_type UNDER person_type AS
( sno VARCHAR(5) NOT NULL
UNIQUE, position VARCHAR(10) NOT
NULL, salary NUMBER(7,2), bno 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
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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!
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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?
The only way of doing this is to declare the
lecturer and admin tables as sub-tables of a
staff super-table!
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ORDBMSs
SQL3 - SUB-TABLES SUPER-TABLES
SUPER-TABLE
SUB-TABLES
SOLUTION TO PROBLEM (FIND ALL STAFF) SQLgt
SELECT FROM staff
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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
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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!
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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
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ORDBMSs
SQL3 - COLLECTION TYPES
EXAMPLE
CREATE TABLE branch ( bno NUMBER(3), address ROW
( street VARCHAR(15), area VARCHAR(15), cit
y VARCHAR(15) staff SET (STAFF_TYPE))
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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
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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 query Still have
Impedance Mismatch!
OODBMSs have been optimised to directly support
object-oriented applications and specific OO
languages.
ORDBMSs are supported by most of the major
players in the DBMS market place.
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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.
OODBMS The 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.
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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
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• 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 of concurrency
  control.

WHEN TO USE AN OODBMS
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WHEN TO USE AN ORDBMS
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• 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 traditional concurrency control is
  acceptable.

WHEN TO USE AN ORDBMS