object (and object-relational) database systems (part two) css263 lecture 18
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Object (and Object-Relational) Database Systems (part two)
CSS263 Lecture 18
LECTURE PLAN
OBJECT DATABASE SYSTEMSPART 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
REMINDER OF THE PROBLEMS ASSOCIATED WITH AN RDBMS
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
WHAT IS AN OODBMS?
OODBMS
OODBMSWHAT 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 PersistenceObject Identity Disc ManagementMethods & Messages Data SharingInheritance ReliabilityPolymorphism SecurityExtensibility Ad Hoc QueryingComputational Completeness
OBJECT ORIENTED DATABASE MANAGEMENT SYSTEM
OODBMSTHE OO DATABASE MANIFESTO
Complex objects Object Identity Encapsulation Classes Inheritance Overriding and late-binding Extensibility Computational completeness Persistence Concurrency Recovery Ad-hoc querying
CHARACTERISTICS THAT ‘MUST BE’ SUPPORTED
REQUIREMENTS AND FEATURES
OODBMSs
Requirements:
Transparently add persistence to OO programming languagesAbility to handle complex data - i.e., Multimedia dataAbility to handle data complexity - i.e., Interrelated data itemsAdd 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
SQL
Transforming andtype checking
Main or virtual memory
Secondarystorage
Record
Record
Record
3. Access object
4. Copy modified fields 2. Copy relevant fields
5. Save page 1. Read page
Page
Page
Page
Ap
pli cation
m
emory
DB
MS
Cach
eS
econd
aryS
torage
ACCESSING A RECORD USING AN RDBMS
Main or virtual memory
Secondarystorage
SINGLE-LEVEL STORAGE MODELFOR AN OODBMS
3. Access object
5. Save page 1. Read page
Page
Page
Ap
pli cation
m
emory
Secon
dary
Storage
Object
Object
4. Swizzle pointers back, etc.
2. Swizzle pointers, etc.
ACCESSING AN OBJECT USING AN OODBMS
ADVANTAGES AND DISADVANTAGES OF AN OODBMS?
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.
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
WHAT IS AN ORDBMS?
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.
MAJOR DIFFERENCE BETWEEN AN ORDBMS AND AN OODBMS
OODBMSs try to add DBMS functionality to one or more OO programming languages.
ORDBMSs
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
SQL3
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!
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.
SQL3 - EXTENDED BASE TYPES
ORDBMSs
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, ...
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!
SQL3 - USER-DEFINED TYPES
ORDBMSs
CREATE TYPE person_type AS (PRIVATE
date_of_birth DATECHECK (date_of_birth > DATE ‘1900-01-
1901’),
PUBLICname 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
*/RETURNEND)
NOT FINAL; An example of a User-Defined Routine (UDR)
SQL3 - SUB-TYPES & SUPER-TYPES
ORDBMSs
PERSON-TYPE
date of birthnameaddresstel-no
get_age()
STAFF-TYPE
snopositionsalarybranch
is_manager()
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!
SQL3 - SUB-TYPES & SUPER-TYPES
ORDBMSs
Another example of a User-Defined Routine (UDR)
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
BEGINIF s.position = ‘Manager’ THEN
RETURN TRUE; ELSE
RETURN FALSE; END IFEND)
NOT FINAL;
SQL3 - TYPES & TABLES
ORDBMSs
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!
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);
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!
SQL3 - SUB-TABLES & SUPER-TABLES
ORDBMSs
CREATE TABLE lecturer OF STAFF_TYPE UNDER staff (PRIMARY KEY sno);
CREATE TABLE admin OF STAFF_TYPE UNDER staff (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;
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_type UNDER person_type AS (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!
SQL3 - REFERENCE TYPES AND OIDS
ORDBMSs
To ensure that a REFERENCE is limited to a single table, a SCOPE has to be added to the table using the REFERENCE!
CREATE TYPE staff_type UNDER person_type AS (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,SCOPE FOR next_of_kin IS person);
staff next_of_kin will point to a row in the person table!)
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 EQUIVALENT OF COLLECTION TYPES IN OODBMSs
KNOWN AS A ‘BAG’ IN AN OODBMS!
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!REPEATING GROUPS ARE ALLOWED!
SQL3 - OTHER ADDITIONS
ORDBMSs
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?
OODBMS or ORDBMSCONSIDERATIONS
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.
OODBMS or ORDBMSCONSIDERATIONS
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 ORDBMSCONSIDERATIONS
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).
WHEN TO USE AN OODBMS
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 of concurrency control.
WHEN TO USE AN ORDBMS
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 traditional concurrency control is acceptable.