1. Object Relational Features
ADVANCED DATABASES
Object Relational Features
Khawaja Mohiuddin
Assistant Professor
Department of Computer Sciences
Bahria University (Karachi Campus)
Contents for this lecture are taken from:
Chapter 10 of “Database Systems: Models, Languages …”, 6th Ed.” by Elmasri and Navathe
(Chapter 11 of “Fundamentals of Database Systems” 6th Ed. by Elmasri and Navathe)

2. Objectives To explain what Object-relation databases are
To cover the Object Database extensions to SQL
To understand how UDTs are declared
To go over examples of following Object Database concepts:
Inheritance
Encapsulation
Reference Type
Instantiability
Referencing and dereferencing attributes

3. Object-Relational Databases
Relational DBMS (RDBMS) vendors recognized need to add object database features.
The resulting database systems characterized as Object-Relational Database Systems or ORDBMS.
SQL first specified by Chamberlin and Boyce (1974), underwent enhancements and standardization in 1989 and New standard, initially called SQL3 and later known as SQL:99
Starting with SQL3 version, features from object databases were incorporated into the SQL standard.
At first, these extensions were known as SQL/Object SQL standard 2008 for RDBMSs includes many ODBMS features - originally known as SQL/Object - now have merged into main SQL specification known as SQL/Foundation.

4. Object-Relational Features: Object Database Extensions to SQL
Relational model with object database enhancements referred to as the object-relational model.
Type constructors
Specify complex objects
Includes the row type (tuple or struct) constructor and array type
set, list, and bag constructors were included later in the standard
Mechanism for specifying object identity included
Encapsulation of operations
Provided through user-defined types (UDTs)
May include operations also
Inheritance mechanisms
Provided using keyword UNDER

5. User-Defined Types (UDT) and Complex Structures for Objects
To allow the creation of complex-structured objects
To separate the declaration of a type from creation of a table
Can be used as either the type for an attribute or as the type for a table
UDT within UDT (complex structure for objects in a table)
UDT syntax:
CREATE TYPE TYPE_NAME AS (<component declarations>);

6. User-Defined Types and Complex Structures for Objects (cont’d.)
UDT example:
CREATE TYPE STREET_ADDR_TYPE AS (
NUMBER VARCHAR (5),
STREET_NAME VARCHAR (25),
APT_NO VARCHAR (5),
SUITE_NO VARCHAR (5) );
CREATE TYPE USA_ADDR_TYPE AS (
STREET_ADDR STREET_ADDR_TYPE,
CITY VARCHAR (25),
ZIP VARCHAR (10)
CREATE TYPE USA_PHONE_TYPE AS (
PHONE_TYPE VARCHAR (5),
AREA_CODE CHAR (3),
PHONE_NUM CHAR (7) );
CREATE TYPE PERSON_TYPE AS (
NAME VARCHAR (35),
SEX CHAR,
BIRTH_DATE DATE,
PHONES USA_PHONE_TYPE ARRAY[4],
ADDR USA_ADDR_TYPE .

7. User-Defined Types and Complex Structures for Objects (cont’d.)
ROW TYPE
Directly create a structured attribute using the keyword ROW if a UDT does not have any operation
CREATE TYPE USA_ADDR_TYPE AS (
STREET_ADDR ROW ( NUMBER VARCHAR (5),
STREET_NAME VARCHAR (25),
APT_NO VARCHAR (5),
SUITE_NO VARCHAR (5) ),
CITY VARCHAR (25),
ZIP VARCHAR (10) );

8. User-Defined Types and Complex Structures for Objects (cont’d.)
Array type
Reference elements using [] Example: PHONES USA_PHONE_TYPE ARRAY[4]
PHONES[1] refers to the first location value in a PHONES attribute
CARDINALITY function
Returns the current number of elements in an array
PHONES[CARDINALITY (PHONES)] refers to the last element in the array
Dot notation:
ADDR.CITY refers to the CITY component of an ADDR attribute

9. Object Identifiers Using Reference Types
Create unique system- generated object identifiers. Example:
REF IS SYSTEM GENERATED
CREATE TYPE PERSON_TYPE AS (
NAME VARCHAR (35),
SEX CHAR,
BIRTH_DATE DATE,
PHONES USA_PHONE_TYPE ARRAY [4],
ADDR USA_ADDR_TYPE
INSTANTIABLE
NOT FINAL
REF IS SYSTEM GENERATED
INSTANCE METHOD AGE() RETURNS INTEGER;
CREATE INSTANCE METHOD AGE() RETURNS INTEGER
FOR PERSON_TYPE
BEGIN
RETURN /* CODE TO CALCULATE A
PERSON’S AGE FROM TODAY’S DATE
AND SELF.BIRTH_DATE */
END; );

10. Object Identifiers Using Reference Types (cont’d.)
Reference type (cont’d.)
Complete Syntax is:
REF IS <OID_ATTRIBUTE> <VALUE_GENERATION_METHOD>;
<OID_ATTRIBUTE> is user declared attribute name to indentify individual tuples in a table
The options for <VALUE_GENERATION_METHOD> are:
SYSTEM GENERATED - system will automatically generate a unique identifier for each tuple
DERIVED - user provided primary key value to identify tuples is applied

11. Creating Tables Based on the UDTs
INSTANTIABLE
Specify that UDT is instantiable (see PERSON_TYPE declaration)
Causes one or more tables to be created
UDTs STREET_ADDR_TYPE and USA_ADDR_TYPE are noninstantiable, and hence can only be used as types for attributes, but not as a basis for table creation
CREATE TABLE PERSON OF PERSON_TYPE
REF IS PERSON_ID SYSTEM GENERATED;
Create a table PERSON based on the PERSON_TYPE UDT
Attribute PERSON_ID will hold the system-generated object identifier whenever a new PERSON record (object) is created and inserted in the table

12. Encapsulation of Operations
User-defined type
Specify methods (or operations) in addition to the attributes
Format:
CREATE TYPE <TYPE-NAME> (
<LIST OF COMPONENT ATTRIBUTES AND THEIR TYPES>
<DECLARATION OF FUNCTIONS (METHODS)> );
Example: method Age() of type PERSON_TYPE

13. Encapsulation of Operations (cont’d.)
Constructor function TYPE_T( )
Returns a new object of that type
Observer function X.A
Returns the value of attribute A of TYPE_T if X is of type TYPE_T
Mutator function
Sets the value of the attribute to a new value
User Defined functions (Internal Functions)
Format
INSTANCE METHOD <NAME> (<ARGUMENT_LIST>) RETURNS
<RETURN_TYPE>;

14. Encapsulation of Operations (cont’d.)
External functions
Written in a host language, with only their signature (interface) appearing in the UDT definition
Format
DECLARE EXTERNAL <FUNCTION_NAME> <SIGNATURE>
LANGUAGE <LANGUAGE_NAME>;
Categories of attributes and functions
PUBLIC (visible at the UDT interface)
PRIVATE (not visible at the UDT interface)
PROTECTED (visible only to subtypes)

15. Specifying Inheritance and Overloading of Functions
Inheritance rules:
All attributes inherited (phrase NOT FINAL must be included)
Order of supertypes in UNDER clause determines inheritance hierarchy
Instance of a subtype can be used in every context in which a supertype instance is used
Subtype can redefine any function defined in supertype
When a function is called, best match selected based on types of all arguments
For dynamic linking, runtime types of parameters is considered

16. Specifying Inheritance and Overloading of Functions (cont’d.)
Example of inheritance of types:
CREATE TYPE EMPLOYEE_TYPE UNDER PERSON_TYPE AS (
JOB_CODE CHAR (4),
SALARY FLOAT,
SSN CHAR (11)
INSTANTIABLE
NOT FINAL );
CREATE TYPE MANAGER_TYPE UNDER EMPLOYEE_TYPE AS (
DEPT_MANAGED CHAR (20)
INSTANTIABLE );
Example of inheritance of tables:
CREATE TABLE EMPLOYEE OF EMPLOYEE_TYPE
UNDER PERSON;
CREATE TABLE MANAGER OF MANAGER_TYPE
UNDER EMPLOYEE;

17. Specifying Relationships via Reference
Component attribute of one tuple may be a reference to a tuple of another table
Specified using keyword REF
Keyword SCOPE
Specify name of table whose tuples referenced
Concept is similar to foreign key
Dot notation
Build path expressions that refer to the component attribute of tuples and row types

18. Specifying Relationships via Reference
–>
Used for dereferencing for an attribute whose type is REF
SELECT E.Employee–>NAME
FROM EMPLOYMENT AS E
WHERE E.Company–>COMP_NAME = ‘ABCXYZ’;
In SQL, –> is has the same meaning assigned to it in the C programming language. Thus, if r is a reference to a tuple and a is a component attribute in that tuple, then r –> a is the value of attribute a in that tuple.

19. Conclusion In this Lecture, we…
To explain what Object-relation databases are
To cover the Object Database extensions to SQL
To understand how UDTs are declared
To go over examples of following Object Database concepts:
Inheritance
Encapsulation
Reference Type
Instantiability
Referencing and dereferencing attributes