1. Object-Oriented Databases

2. Outline Advanced database applications Shortcomings of Relational DBs
Object-oriented concepts
Object Relational Systems (ORDBMSs)
SQL:1999 object extensions
Object-oriented database Systems (OODBMSs)
ODMG Data Model
ODL – data definition language
OQL – query language

3. Advanced Database Applications
Computer-Aided Design/Manufacturing (CAD/CAM)
Computer-Aided Software Engineering (CASE)
Network Management Systems
Office Information Systems (OIS) and Multimedia Systems
Digital Publishing
Geographic Information Systems (GIS)
Interactive and Dynamic Web sites
Other applications with complex and interrelated objects and procedural data.

4. Expected features for new applications
Complex objects
Behavioral data
Meta knowledge
Long duration transactions

5. Weaknesses of RDBMSs Poor representation of “Real World” entities
Normalization leads to relations that do not correspond to entities in “real world”.
Semantic overloading
Relational model has only one construct for representing data and data relationships: the relation.
Relational model is semantically overloaded

6. Weaknesses of RDBMSs Limited operations
only a fixed set of operations which cannot be extended.
Difficulty handling recursive queries
Impedance mismatch
Most DMLs lack computational completeness.
To overcome this, SQL can be embedded in a high-level language.
This produces an impedance mismatch - mixing different programming paradigms.
Estimated that as much as 30% of programming effort and code space is expended on this type of conversion.

7. Object-Oriented Concepts
Abstraction, encapsulation, information hiding.
Objects and attributes.
Object identity.
Methods and messages.
Classes, subclasses, superclasses, and inheritance.
Overloading.
Polymorphism and dynamic binding.

8. Complex Objects
An object that consists of sub-objects but is viewed as a single object.
Objects participate in a A-PART-OF relationship.
Contained object can be encapsulated within complex object, accessed by complex object’s methods.
Or have its own independent existence, and only an OID is stored in complex object.

9. Database Systems First Generation DBMS: Network and Hierarchical
Required complex programs for even simple queries.
Minimal data independence.
No widely accepted theoretical foundation.
Second Generation DBMS: Relational DBMS
Helped overcome these problems.
Third Generation DBMS: OODBMS and ORDBMS.

10. History of Data Models

11. Origins of the Object-Oriented Data Model

12. ORDBMS

13. ORDBMSs Vendors of RDBMSs conscious of threat and promise of OODBMS.
Agree that RDBMSs not currently suited to advanced database applications, and added functionality is required.
Reject claim that extended RDBMSs will not provide sufficient functionality or will be too slow to cope adequately with new complexity.
Can remedy shortcomings of relational model by extending model with OO features.

14. ORDBMSs - Features OO features being added include:
user-extensible types,
encapsulation,
inheritance,
polymorphism,
dynamic binding of methods,
complex objects including non-1NF objects,
object identity.

15. Stonebraker’s View

16. Objects in SQL:1999 Object-relational extension of SQL-92
Includes the legacy relational model
SQL:1999 database = a finite set of relations
relation = a set of tuples (extends legacy relations) OR
a set of objects (completely new)
object = (oid, tuple-value)
tuple = tuple-value
tuple-value = [Attr1: v1, …, Attrn: vn]

17. SQL:1999 Tuple Values Tuple value: [Attr1: v1, …, Attrn: vn]
Attri are all distinct attributes
Each vi is one of these:
Primitive value: a constant of type CHAR(…), INTEGER, FLOAT, etc.
Reference value: an object Id
Another tuple value
A collection value
Only the ARRAY construct is – a fixed size array.
SETOF and LISTOF are not supported.

18. Row Types
The same as the original (legacy) relational tuple type. However:
Row types can now be the types of the individual attributes in a tuple
CREATE TABLE PERSON (
Name CHAR(20),
Address ROW(Number INTEGER, Street CHAR(20), ZIP CHAR(5)) )

19. Row Types (Contd.)
Use path expressions to refer to the components of row types:
SELECT P.Name
FROM PERSON P
WHERE P.Address.ZIP = ‘11794’
Update operations:
INSERT INTO PERSON(Name, Address)
VALUES (‘John Doe’, ROW(666, ‘Hollow Rd.’, ‘66666’))
UPDATE PERSON
SET Address.ZIP = ‘66666’
WHERE Address.ZIP = ‘55555’
SET Address = ROW(21, ‘Main St’, ‘12345’)
WHERE Address = ROW(123, ‘Maple Dr.’, ‘54321’) AND Name = ‘J. Public’

20. User Defined Types (UDT)
UDTs allow specification of complex objects/tuples, methods, and their implementation
Like ROW types, UDTs can be types of individual attributes in tuples
UDTs can be much more complex than ROW types (even disregarding the methods): the components of UDTs do not need to be elementary types

21. File that holds the binary code
A UDT Example
CREATE TYPE PersonType AS (
Name CHAR(20),
Address ROW(Number INTEGER, Street CHAR(20), ZIP CHAR(5)) );
CREATE TYPE StudentType UNDER PersonType AS (
Id INTEGER,
Status CHAR(2) )
METHOD award_degree() RETURNS BOOLEAN;
CREATE METHOD award_degree() FOR StudentType
LANGUAGE C
EXTERNAL NAME ‘file:/home/admin/award_degree’;
File that holds the binary code

22. Using UDTs in CREATE TABLE
As an attribute type:
CREATE TABLE TRANSCRIPT (
Student StudentType,
CrsCode CHAR(6),
Semester CHAR(6),
Grade CHAR(1) )
As a table type:
CREATE TABLE STUDENT OF StudentType;
Such a table is called typed table.
A previously defined UDT

23. Objects Only typed tables contain objects (ie, tuples with oids)
Compare:
CREATE TABLE STUDENT OF StudentType;
and
CREATE TABLE STUDENT1 (
Name CHAR(20),
Address ROW(Number INTEGER, Street CHAR(20), ZIP CHAR(5)),
Id INTEGER,
Status CHAR(2) )
Both contain tuples of exactly the same structure
Only the tuples in STUDENT – not STUDENT1 – have oids.
This disparity is motivated by the need to stay backward compatible with SQL-92.

24. Querying UDTs Nothing special – just use path expressions
SELECT T.Student.Name, T.Grade
FROM TRANSCRIPT T
WHERE T.Student.Address.Street = ‘Main St.’
Note: T.Student has the type StudentType. The attribute Name is not declared explicitly in StudentType, but is inherited from PersonType.

25. Updating User-Defined Types
Inserting a record into TRANSCRIPT:
INSERT INTO TRANSCRIPT(Student,Course,Semester,Grade)
VALUES (????, ‘CS308’, ‘2000’, ‘A’)
The type of the Student attribute is StudentType. How does one insert a value of this type (in place of ????)?
Further complication: the UDT StudentType is encapsulated, ie, it is accessible only through public methods, which we did not define
Do it through the observer and mutator methods provided by the DBMS automatically

26. Observer Methods
For each attribute A of type T in a UDT, an SQL:1999 DBMS is supposed to supply an observer method, A: ( )  T, which returns the value of A (the notation “( )” means that the method takes no arguments)
Observer methods for StudentType:
Id: ( )  INTEGER
Name: ( )  CHAR(20)
Status: ( )  CHAR(2)
Address: ( )  ROW(INTEGER, CHAR(20), CHAR(5))
For example, in
SELECT T.Student.Name, T.Grade
FROM TRANSCRIPT T
WHERE T.Student.Address.Street = ‘Main St.’
Name and Address are observer methods, since T.Student is of type StudentType
Note: Grade is not an observer, because TRANSCRIPT is not part of a UDT

27. Mutator Methods
An SQL:1999 DBMS is supposed to supply, for each attribute A of type T in a UDT U, a mutator method
A: T  U
For any object o of type U, it takes a value t of type T
and replaces the old value of o.A with t; it returns the
new value of the object. Thus, o.A(t) is an object of type U
Mutators for StudentType:
Id: INTEGER  StudentType
Name: CHAR(20)  StudentType
Address: ROW(INTEGER, CHAR(20), CHAR(5))  StudentType

28. Example: Inserting a UDT Value
INSERT INTO TRANSCRIPT(Student,Course,Semester,Grade)
VALUES (
NEW StudentType( ) .Id( ) .Status(‘G5’) .Name(‘Joe Public’)
.Address(ROW(123,’Main St.’, ‘54321’)) ,
‘CS532’,
‘S2002’,
‘A’ )
‘CS532’, ‘S2002’, ‘A’ are primitive values for the attributes Course, Semester, Grade
Add a value for Id
Add a value for the Address attribute
Create a blank StudentType object
Add a value for Status

29. Example: Changing a UDT Value
UPDATE TRANSCRIPT
SET Student = Student.Address(ROW(21,’Maple St.’,’12345’)).Name(‘John Smith’),
Grade = ‘B’
WHERE Student.Id = AND CrsCode = ‘CS532’ AND Semester = ‘S2002’
Mutators are used to change the values of the attributes Address and Name
Change Name
Change Address

30. Referencing Objects Consider again CREATE TABLE TRANSCRIPT (
Student StudentType,
CrsCode CHAR(6),
Semester CHAR(6),
Grade CHAR(1) )
Problem: TRANSCRIPT records for the same student refer to distinct values of type StudentType (even though the contents of these values may be the same) – a maintenance/consistency problem
Solution: use self-referencing column
Bad design, which distinguishes objects from their references
Not truly object-oriented

31. Self-Referencing Column
Every typed table has a self-referencing column
Normally invisible
Contains explicit object Id for each tuple in the table
Can be given an explicit name – the only way to enable referencing of objects
CREATE TABLE STUDENT2 OF StudentType
REF IS stud_oid;
Self-referencing columns can be used in queries just like regular columns
Their values cannot be changed, however
Self-referencing column

32. Reference Types and Self-Referencing Columns
To reference objects, use self-referencing columns + reference types: REF(some-UDT)
CREATE TABLE TRANSCRIPT1 (
Student REF(StudentType) SCOPE STUDENT2,
CrsCode CHAR(6),
Semester CHAR(6),
Grade CHAR(1) )
Two issues:
How does one query the attributes of a reference type
How does one provide values for the attributes of type REF(…)
Remember: you can’t manufacture these values out of thin air – they are oids!
Reference type
Typed table where the values are drawn from

33. Querying Reference Types
Recall: Student REF(StudentType) SCOPE STUDENT2 in TRANSCRIPT1. How does one access, for example, student names?
SQL:1999 has the same misfeature as C/C++ has (and which Java and OQL do not have): it distinguishes between objects and references to objects. To pass through a boundary of REF(…) use “” instead of “.”
SELECT T.StudentName, T.Grade
FROM TRANSCRIPT1 T
WHERE
T.StudentAddress.Street = “Main St.”
Not crossing REF(…) boundary, use “.”
Crossing REF(…) boundary, use 

34. Explicit self-referential column of STUDENT2
Inserting REF Values
How does one give values to REF attributes, like Student in TRANSCRIPT1?
Use explicit self-referencing columns, like stud_oid in STUDENT2
Example: Creating a TRANSCRIPT1 record whose Student attribute has an object reference to an object in STUDENT2:
INSERT INTO TRANSCRIPT1(Student,Course,Semester,Grade)
SELECT S.stud_oid, ‘HIS666’, ‘F1462’, ‘D’
FROM STUDENT2 S
WHERE S.Id = ‘ ’
Explicit self-referential column of STUDENT2

35. Object-Oriented Oracle An Analysis of the Object-Oriented Features of Oracle’s Database Management System

36. Background
Beginning with Oracle 8 Universal Data Server, Oracle started implementing object-oriented (OO) principals within the database management system.
Oracle is not a true OO database – object-relational.
Oracle’s goals for OO support:
Allow users to model business objects via types.
Provide infrastructure to support OO access.

37. OO Features/Advantages of Objects in Oracle
Abstraction
Encapsulation
Inheritance
Advantages:
Object re-use
Use of methods
Efficiencies
Model real-world business objects

38. Object Type Implementation
Creating Types
Similar to creating a “class” with attributes:
CREATE TYPE addr_ty AS OBJECT
(street varchar2(60),
city var char2(30),
state char(2),
zip varchar(9));

39. Object Type Implementation
Imbedding Objects and Nesting
Create a person type with address type nested inside:
CREATE TYPE person_ty AS OBJECT
(name varchar2(25),
address addr_ty);
Create a student type with person type nested inside:
CREATE TYPE student_ty AS OBJECT
(student_id varchar2(9),
person person_ty);

40. Object Type Implementation
Creating an Object Table
Now that the student_ty object type has been defined it can be used in creating an object table like the following:
CREATE TABLE STUDENT
(full_student student_ty);

41. Object Type Implementation
To extract data, the following query can be entered:
SELECT s.full_student.student_id ID, s.full_student.person.name NAME, s.full_student.person.address.street STREET
FROM student s
WHERE s.full_student.student_id = 100
 ID NAME STREET
John Q. Student Chastain Rd.

42. Object Type Implementation
Updating and deleting is similar to what one would do in the relational model:
UPDATE STUDENT s
SET s.full_student.person.name = 'JOHN NEWNAME'
WHERE s.full_student.student_id = 100;
DELETE FROM STUDENT s

43. Implementing Methods To define a method in a type object:
create or replace type newperson_ty as object (firstname varchar2(25),
lastname varchar2(25),
birthdate date,
member function AGE(BirthDate in DATE) return NUMBER;
Then define the method itself:
create or replace type body newperson_ty as
member function AGE(BirthDate in DATE) return NUMBER is
begin
RETURN ROUND(SysDate - BirthDate);
end;

44. Implementing Methods
To test the method first set up a table holding the person_ty object type:
create table NEWPERSON of newperson_ty;
insert into NEWPERSON values
(newperson_ty('JOHN', 'DOE', TO_DATE('03-FEB-1970', 'DD-MON-YYYY')));
To call the AGE function we can do the following:
select P.PERSON.AGE(P.PERSON.Birthdate)
from NEWPERSON P;
P.PERSON.AGE(P.PERSON.Birthdate)
12005

45. Referencing
Every row object has a unique identifier called the object identifier (OID).
OID allows other objects to reference an existing row object.
REF function can be used to reference an OID:
create table NEWDEPARTMENT
(DeptName VARCHAR(30),
PersonIn REF NEWPERSON_TY);
Table NEWDEPARTMENT holds a reference to a NEWPERSON_TY object, but does not hold any real values.

46. Referencing To get a full description of the table just created:
Set describe depth 2
Desc NEWDEPARTMENT
Name Null? Type
DEPTNAME VARCHAR2(30)
PERSONIN REF OF NEWPERSON_TY
FIRSTNAME VARCHAR2(25)
LASTNAME VARCHAR2(25)
BIRTHDATE DATE

47. Referencing
To insert a record into NEWDEPARTMENT, the REF is needed to store the NEWPERSON reference in the PersonIn column:
insert into NEWDEPARTMENT
select 'Research',REF(P)
from NEWPERSON P
where LastName = 'DOE';
The literal value “Research” is inserted into the NEWPERSON table.
The REF function returns the OID from the query on the selected NEWPERSON object.
The OID is now stored as a pointer to the row object in the NEWPERSON object table.

48. Referencing
The referenced value cannot be seen unless the DREF function is used. The DREF function takes the OID and evaluates the reference to return a value.
select DEREF(D.PersonIn)
from NEWDEPARTMENT D
where DEPTNAME = 'Research'
DEREF(D.PERSONIN)(FIRSTNAME, LASTNAME, BIRTHDATE)
NEWPERSON_TY('JOHN', 'DOE', '03-FEB-70')
This shows that the NEWPERSON record JOHN DOE is referenced by the Research record in NEWDEPARTMENT.

49. Referencing
To gather the same structure of the object type of an object table the VALUE function is required.
select value(p)
from newperson p
where lastname = 'DOE'
VALUE(P)(FIRSTNAME, LASTNAME, BIRTHDATE)
NEWPERSON_TY('JOHN', 'DOE', '03-FEB-70')

50. Referencing PL/SQL Sample: set serveroutput on declare
v_person NEWPERSON_TY;
begin
select value(p) into v_person
from NEWPERSON p
where lastname = 'DOE';
DBMS_OUTPUT.PUT_LINE(v_person.firstname);
DBMS_OUTPUT.PUT_LINE(v_person.lastname);
DBMS_OUTPUT.PUT_LINE(v_person.birthdate);
end;   
JOHN
DOE
03-FEB-70

51. Inheritance Create a root type of an object hierarchy:
create type PERSON_TY as object
(name varchar2(25),
birthdate date,
member function AGE() return number,
member function PRINTME() return varchar2);
To create a subtype the following syntax can be used:
create type EMPLOYEE_TY under PERSON_TY (
salary number,
member function WAGES() return number,
overriding member function PRINTME() return varchar2);

52. OODBMS

53. Object-Oriented Data Model
No one agreed object data model. One definition:
Object-Oriented Data Model (OODM)
Data model that captures semantics of objects supported in object-oriented programming.
Object-Oriented Database (OODB)
Persistent and sharable collection of objects defined by an ODM.
Object-Oriented DBMS (OODBMS)
Manager of an ODB.

54. Commercial OODBMSs GemStone from Gemstone Systems Inc.,
Objectivity/DB from Objectivity Inc.,
ObjectStore from Progress Software Corp.,
Ontos from Ontos Inc.,
FastObjects from Poet Software Corp.,
Jasmine from Computer Associates/Fujitsu,
Versant from Versant Corp.

55. Advantages of OODBMSs Enriched Modeling Capabilities.
Removal of Impedance Mismatch.
More Expressive Query Language.
Support for Schema Evolution.
Support for Long Duration Transactions.
Applicability to Advanced Database Applications.

56. Disadvantages of OODBMSs
Lack of Universal Data Model.
Lack of Experience.
Lack of Standards.
Query Optimization compromises Encapsulation.
Object Level Locking may impact Performance.
Complexity.

57. Alternative Strategies for Developing an OODBMS
Extend existing object-oriented programming language.
GemStone extended Smalltalk.
Provide extensible OODBMS library.
Approach taken by Ontos, Versant, and ObjectStore.
Embed OODB language constructs in a conventional host language.
Approach taken by O2,which has extensions for C.
Extend existing database language with object-oriented capabilities.
Approach being pursued by RDBMS and OODBMS vendors.
Ontos and Versant provide a version of OSQL.
Develop a novel database data model/language.

58. Single-Level v. Two-Level Storage Model
With a traditional DBMS, programmer has to:
Decide when to read and update objects.
Write code to translate between application’s object model and the data model of the DBMS.
Perform additional type-checking when object is read back from database, to guarantee object will conform to its original type.
Conventional DBMSs have two-level storage model: storage model in memory, and database storage model on disk.
In contrast, OODBMS gives illusion of single-level storage model, with similar representation in both memory and in database stored on disk.

59. Two-Level Storage Model for RDBMS

60. Single-Level Storage Model for OODBMS

61. Object Data Management Group (ODMG)
Established by vendors of OODBMSs to define standards.
The ODMG Standard includes :
Object Data Model (ODM).
Object Definition Language (ODL).
Object Query Language (OQL).
C++, Smalltalk, and Java Language Binding.

62. The Structure of an ODMG Application

63. Main Idea: Host Language = Data Language
Objects in the host language are mapped directly to database objects
Some objects in the host program are persistent. Changing such objects (through an assignment to an instance variable or with a method application) directly and transparently affects the corresponding database object
Accessing an object using its oid causes an “object fault” similar to pagefaults in operating systems. This transparently brings the object into the memory and the program works with it as if it were a regular object defined, for example, in the host Java program

64. Architecture of an ODMG DBMS

65. SQL Databases vs. ODMG
In SQL: Host program accesses the database by sending SQL queries to it (using JDBC, ODBC, Embedded SQL, etc.)
In ODMG: Host program works with database objects directly