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CHAPTER 11

Concepts for

Object-Oriented Databases

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Overview of

Object-Oriented Concepts Object-oriented databases give designer to specify

The structure of complex objects

The operations that can be applied to objects

Increase uses of OOPL

Object

State(Value)

Behavior(operations)

transient vs. persistent

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Overview of

Object-Oriented Concepts (Cont.) Maintain a direct correspondence between

real-world and database objects

A real-world object may have different names

for key attributes in different relations in

traditional database systemsE.G. EMP_ID, SSN in different relations

OODBs provide a unique system-

generated object identifier for each object

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Overview of

Object-Oriented Concepts (Cont.)

Objects may have an object structure of

arbitrary complexity

Information about a complex object is often

scatteredover many relations or records in

traditional database systems

1NF in relational databases

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Object Identity unique identity for each independent object

stored in the database

created by a unique, system-generated

object identifier, or OID

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Object Identity (Cont.)

properties of OID

immutable: the OID value of a particular objectshould not change

Each OID is used only once.

OID should not depend on any physical addressattribute values of the object

Most OO database systems allow for the representation ofboth objects and values (having no OIDs)

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Object Structure

(i, c, v)

i: a unique object identifier(OID)

c: a type constructor

basic type: atom

structured type: tuple collection type: array vs. list, set vs. bag

System supports

(integer,real,string,Boolean,)

number of

elementsdistinct vs.

duplicate

order unorder

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v: object state

c=atom ::: an atomic value from the domain

c=set ::: a set of object identifiers {i1, i2, , in}

c=tuple ::: a tuple of

c=list ::: an ordered list [i1, i2, , in]

c=array ::: a single-dimensional array of object

identifiers

c=bag

Object Structure (Cont.)

iijj : OID: OID

aajj : attribute name: attribute name

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Example 1: Complex Object

EMPLOYEE FNAME MINIT LNAME SSN BDATE ADDRESS SEX SALARY SUPERSSN DNO

John B mith 123456789 09-J N-55 731 Fondren, ouston, TX 30000 333445555 5

Franklin T Wong 333445555 08- EC-45 638 Voss, ouston, TX 40000 888665555 5

licia J Zelaya 999887777 19-JU -58 3321 Castle, pring, TX F 25000 987654321 4

Jenni er Wallace 987654321 20-JUN-31 291 Berry, Bellaire, TX F 43000 888665555 4

amesh K Narayan 666884444 15- E -52 975 Fire Oak, umble, TX 38000 333445555 5

Joyce English 453453453 31-JU -62 5631 ice, ouston, TX F 25000 333445555 5

hmad V Jabbar 987987987 29- -59 980 allas, oustom TX 25000 987654321 4

James E Borg 888665555 10-NOV-27 450 tone, ouston, T 55000 null 1

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Example 1: Complex Object (Cont.)

o1=(i1,atom,Houston)

o2=(i2,atom, ellaire)

o3=(i3,atom,Sugarland) o4=(i4,atom,5)

o5=(i5,atom,Research)

o6=(i

6,atom,1988-05-22)

o7=(i5,set,{i1, i2, i3}) ::: the set of locations for

department 5

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o8=(i8, tuple, ) ::: department 5

o9=(i9, tuple, )

o10=(i10,set,{i12, i13, i14})

o11

=(i11

,set,{i15

, i16

, i17

})

o12=(i12, tuple, < AME:i18, MI IT: i19, L AME:i20, SS : i21, , SALARY: i26, S PER ISOR: i27,DEPT: i28>)

Example 1: Complex Object (Cont.)

employee John B. Smith

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Graphical representation of a complex object

LEGE D: object

tuple

set

D AME D M ER MGR LOCATIO S EMPLOYEES PROJECTS

MA AGER MA AGERSTRATDATE

O5 O4 O9 O7O

10O

11

O8

O1 O2 O3

Houston ellaire Sugarland

i8:

tuple

i5:

atom

i4:

atom i9:

tuplei7:

seti10:

seti11:

set

i15: .....

tuple

i16: .....

tuple

i17: .....

tuple

i12: .....

tuple

i13: .....

tuple

i14: .....

tuple

i6:

atom

O6

1988-05-22

4

9

5

7

10

11

1 2 3

6

Research 5

Object instance ofObject instance of

department typedepartment type

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Comparisons of the states of

two objects for equality identical states (deep equality)

the graphs representing their states are identical in

every respect, including the OIDs at every level equal states (shallow equality)

the graph structures must be the same

all the corresponding atomic values in the graphs

should be the same allow some corresponding internal nodes in the two

graphs to have objects with differentOIDs

(Current Values)(Current Values)

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Example 2:

Identical vs. Equal Object States o1=(i1, tuple, )

o2=(i2, tuple, )

o3=(i3, tuple, )

o4=(i4, atom, 10)o5=(i5, atom, 10)

o6=(i6, atom, 20)

o1

and o2

have equal states

o1 and o3 have identical states

o4 and o5 have identical states

o4 and o5 are equal but not identical

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sing OODDL to define Employee, Date, and

Department types

define typetuple (

Employee:fname:minit:lname:

ssn:birthdate:addresssex:salary:supervisor:

dept:

string;char;string;

string;Date;string;char;float;Employee;

Department);

Attributes refer to Employee,Attributes refer to Employee,

Department objectsDepartment objects

relationship among objectsrelationship among objects

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define typetuple (

define typetuple (

Date:year:month:

day:

Departmentdname:dnumber:

mgr:

locations:employees:

projects:

integer;integer;integer; );

string;integer;

tuple (manager:startdate:

set (string);set (Employee);set (Project); );

Employee;Date; );

sing OODDL to define Employee, Date, and

Department types (Cont.)

Inverse reference:Inverse reference:

dept. of employeedept. of employee

employee of dept.employee of dept.

set of referencesset of references

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Specifying Object ehavior

via Class Operations

Define theb

ehavior of a type of object basedon the operations that can be externallyapplied to object of that type

create (insert) or destroy (delete) objects

update the object state retrieve parts of the object state

apply some calculations

combination of retrieval, calculation, and update

In relational model, selecting, inserting, deletingIn relational model, selecting, inserting, deletingand modifying tuples areand modifying tuples are genericgeneric..

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Specifying Object ehavior

via Class Operations (Continued)

interface

define the name and arguments (parameters) of each

operation

signature (included in the class definition)

implementation method (defined using programming languages)

it is invoked by sending a message to the object to

execute the corresponding method

Operations 1. object constructorsOperations 1. object constructors2. object destructor2. object destructor3. object modifier3. object modifier4. retrieval4. retrieval

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sing OODDL to define Employee and

Department classes

operations age

create_emp:

destroy_emp :

end Employee;

integer;

Employee;

boolean;

define classtype tuple (

Employee:fname:minit:lname:ssn:

birthdate:addresssex:salary:supervisor:dept:

string;char;string;string;

Date;string;char;float;Employee;Department);

typedefinition

definition

of

operations

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sing OODDL to define Employee and

Department classes (Continued)

define class

type tuple (

Department

dname:dnumber:mgr:

locations:employees:projects:

string;integer;tuple (manager:

startdate:

set (string);set (Employee);set (Project); );

Employee;Date; );

operations

number_of_emps : integer;

create_dept: Department,destroy_dept: boolean;

assign_emp (e: Employee): boolean;

(* adds a new employee to the department *)

remove_emp (e: Employee): boolean;

(* removes an employee from the department *)

end Department;

type

definition

definition

of

operations

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Class Operations

object constructor create a new object

destructor

destroy an object object modifier

modify various attribute of an object

dot notation d.no_of_emps where d is a reference to a

department object and no_of_emps is an operation

refer to attributes of an object: d.dnumber, d.mgr.startdate

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Specifying Object Persistence via

aming and Reachability transient object

exist in the executing program and disappear once

the program terminates persistent object

stored in the database and persist after program

termination

naming mechanism

give an object a unique persistent name through

which it can be retrieved by this and other program

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Reachability

reachability mechanism

make the object reachable from some persistent object

an object is said to be reachable from an object A if asequence of references in the object graph lead from

object A to object e.g., if o8 is persistent, then all other objects also

become persistent (next slide)

defines a persistent collection of objects of class C

create a named persistent object , whose state is aset or list of objects of some class C

add objects of C to the set or list and make themreachable from

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Graphical representation of a complex object

LEGE D: object

tuple

set

D AME D M ER MGR LOCATIO S EMPLOYEES PROJECTS

MA AGER MA AGERSTRATDATE

O5

O4

O9

O7

O10 O11

O8

O1 O2 O3

Houston ellaire Sugarland

i8:

tuple

i5:

atom

i4:

atom i9:tuplei7:

seti10:

seti11:

set

i15: .....

tuple

i16: .....

tuple

i17: .....

tuple

i12: .....

tuple

i13: .....

tuple

i14: .....

tuple

i6:

atom

O6

1988-05-22

4

9

5

7

10

11

1 2 3

6

Research 5

Object instance ofObject instance of

department typedepartment type

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Creating persistent objects by naming and reachability

define class DepartmentSet:

type set (Department);

operations

add_dept(d: Department): boolean;

remove_dept (d: Department): boolean,

create_dept_set: DepartmentSet;

destroy_dept_set: boolean;end DepartmentSet;

persistent name AllDepartments: DepartmentSet ;

(* AllDepartments is a persistent named object of type set DepartmentSet*)

.....d := create_dept ;

..... (* creates a new department object in the variable d *)

b := AllDepartments.add_dept (d) ;

(* make d persistent by adding it to the persistent named object AllDepartments *)

AllDepartments object: extent of the class Department

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differences between traditional

databases and OO databases traditional database models

when an entity type or class is defined in EER,

it represents both type declaration andpersistent set

OO approaches

a class declaration specifies only the type andoperations for a class of objects

user must define a persistent object whose

value is the collection of references to all

persistent

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Type Hierarchies and Inheritance

type (or class) hierarchy define new types based on other predefined types (or

classes)

type

type name a number of attributes (instance variables)

operations (methods)

TYPE_ AME: function, function, , function

PERSO : ame, Address, irthdate, Age, SSEMPLOYEE subtype-of PERSO : Salary,

HireDate, SeniorityST DE T subtype-of PERSO : Major, GPA

functions with zero arguments

functions

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GEOMETRY_O JECT: Shape, Area, ReferencePoint

RECTA GLE subtype-ofGEOMETRY_O JECT: Width, Height

TRIA GLE subtype-of

GEOMETRY_O JECT: Side1, Side2, Side3

CIRCLE subtype-of GEOMETRY_O JECT:

Radius

attributes(triangle,rectangle,circle)

method attribute

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(Cont.)

RECTA GLERECTA GLE subtype-of

GEOMETRY_O JECT (Shape=rectangle): Width, Height

TRIA GLETRIA GLE subtype-of

GEOMETRY_O JECT (Shape=triangle): Side1, Side2, Side3

CIRCLECIRCLE subtype-of

GEOMETRY_O JECT (Shape=circle): Radius

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Inheritance multiple inheritance

when T is a subtype of two (or more) types, T inheritsthe functions (attributes and methods) of both

supertypes

type lattice instead of type hierarchy

if a function is inherited from some common supertype,it is inherited only once

ambiguity resolution alarm users

system default

disallow multiple inheritance

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Inheritance (Continued) Selective Inheritance

a subtype inherits only some of the functions of

a supertype

an E CEPT clause may be used to list the

functions in a super type that are notto be

inherited by the subtype

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