Transcript ADB-Lecture10-ObjectOrientedDBMS

Object-Oriented
DBMS
Lecture 10
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Relational DBMS’ Shortcomings
Lengthy query execution for simple queries
due to joins
Lack of hierarchy, a student is a special kind of
person
Should know the interrelation of tables to write
queries
Impossible to write a complete program using
only query languages like SQL
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Relational DBMS’ Shortcomings..
 No support of ADT
 To many Index files
 The need for normalization to remove inconsistency…
 Difficult to understand the relational representation
 Difficult to represent updates, update operations do not
correspond to the real world update operations.
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Advantages of OO DBMS
 Closer to real world objects
 Reduction of code
 Increase of application programmer’s understanding capability
 Reliability
 Maintainability
 Ability to store/retrieve objects
 Objects can be of complex types
 Hierarchical structure and inheritance
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Advantages of OODBMS…
 Support of complex Objects
 Homogenization of heterogeneity
in media, system, and others by regarding everything as an
object, whereby the followings can be realized:
 multimedia DBMS
 multi database system
 interoperability among resources
ex) OMG (Object Management Group)
 Consistent information system
development can be possible
OOA + OOD + OOP + OODB
(Analysis)
(Design)
(Programming)
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Advantages of OODBMS…
Exact representation
Exact database update operation
High performance
Others… Reuse of codes, …
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DBMS Generation
 OODBMS is the 3rd Generation DBMS
 1G DBMS
1968 IMS … IBM product
known as the hierarchical DBMS
 2G DBMS
1970 Relational data model by E.F.Codd
1980’s Relational DBMS products Ingres, DB2, Oracle, …
1990 … the number of newly installed relational DBMSs exceeded
those of the 1G DBMSs
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DBMS Generation…
 2.5 DBMS
Late `80s … Extended relational DBMS
Startburst, Postgres, UniSQL/X => Informix universal server,
Oracle V.8
 3G DBMS
In 90’s .. Object-Oriented DBMS products
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Major DBMS applications
 Two Major DB Management Areas:
1. Business(or Traditional) database management area
 business database management
Employee management
Sales management
Inventory management, …
1G DBMS : Network DBMS
Hierarchical DBMS
2G DBMS : Relational DBMS
1 real world object : 1 tuple of a relation
ex. an employee :
1 tuple of relation Employee
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Major DBMS applications…
2. Non-business (or Advanced) database management area
 Advanced database management Database management for
CAD
CASE
Multimedia
Information system
…
 3G DBMS: Object-Oriented DBMS
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Relational DBMS vs. OO DBMS
 Support of complex objects
A relational approach :
(a) A sample module
(b) A structural analysis
Module
X1 11 A
X2 12 B
101
13
Connection
y
103
A
B
102
14
15
D Q
104
Y
IS-PART-OF
Element
IS-PART-OF
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Terminal
Module 7
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Why Object-Oriented DBMS?(4)
(c) A relational representation of the module
Module
Terminal
ModuleID ModuleName
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Module 7
Element
ModuleID ElementID ModuleName
7
101
2 inp. XNOR
7
102
2 inp.NAND
7
103
2 inp.NAND
7
104
Latch
Connection
ModuleID CommectionID ConnName
7
11
X1
7
12
X2
7
13
7
14
7
15
y
7
16
Y
ModuleID CommectionID TermName I/O
101
11
A
I
101
12
B
I
101
13
XNOR(A,B) O
102
12
A
I
102
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B
I
102
14
NAND(A,B) O
103
13
A
I
103
14
B
I
103
15
NAND(A,B) O
104
15
D
I
104
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Q
O
 Problems
a) A lot of tuples
b) Difficult to imagine the original object
c) (Display) Process is slow
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Why Object-Oriented DBMS?(5)
An Object-Oriented Approach
 Benefits
1) Natural Representation
2) Direct Manipulation
(a) Object-oriented representation of module7-concept
Element
Module
elementName

moduleNumber
moduleName

connectedLine
elementNumber
terminalName
terminalParts
terminalNumber
input/output
elementParts
connectionParts
Terminal
Connection

connectionName
connectNumber
(b) Object-oriented representation of module7-schema
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Why Object-Oriented DBMS?(6)
XNOR
101
module7
7
NAND
102
X1
11
X2
12


A
01
input
B
02
input


(c) Object-oriented representation of Module7-instance
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An Object-Oriented Approach
: ONTOS Notation
class Module: public Object {
private:
int priv_moduleNum;
char priv_moduleName;
Set priv_elementParts;
Set priv_connectionParts;
public:
Module(int moduleNum, char moduleName);
/ accessors /
Set elementParts() {return priv_elementParts;};
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An Object-Oriented Approach
: ONTOS Notation…
void elementExchange(int elementNum1, int
elementNum2);
…
}
(a) Schema Definition of class Module
Module currentModule=new Module(7, “Module7”);
(b) Creation of Module7 in a C++ program
currentModule->elementExchange(101,102);
(C) Element exchange-an example
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What is OODBMS?
 Object-Oriented data model:
 The data modeling concept is same among 1G, 2G and 3G data
modeling.
 The data models are different.
There is a paradigm shift between the 1G & 2G data model and 3G
data model, i.e. object-oriented data model.
 Unfortunately, there is no standard object-oriented data model.(but
recently, ODMG-93)
 Most of the current object-oriented data models depend on either
the Smalltalk or the C++ object-orientation.
 Therefore, it is necessary to understand the object-orientation
concepts given by those programming languages.
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Some object modeling techniques





Rumbough Model: OMT (Object modeling technique)
Information Engineering model: IE/O by Dodd and Short
Booch model
Jacobson model: OOSE
UML: Unified Modeling Language by Jacobson+booch+Rumbough
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What is Object-Orientation?
 Basic concepts:
Object
Method
Message
Class
Instance
Inheritance
Encapsulation
Polymorphism
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What is Object-Orientation?...
 Object
 Representation of a real world object.
As it is, natural, …
 Encapsulation is done
Variables and methods (i.e. data and procedures) are encapsulated
 Communication between objects is done by sending messages.
 Object has object identity
Object identity is realized by assigning unique OIDs to database
objects. OID is different from TID in the relational DB
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What is Object-Orientation?...
 Class
A template for defining the methods and variable for a
particular type of objects
&
Repository of the particular type of objects
An object is an instance of a particular class
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What is Object-Orientation?...
[Example]
Class Aircraft
Subclass Airplane
Subclass PropellerAirplane
Subclass JetAirplane
…
Subclass Boeing747
Subclass Helicopter
Subclass Glider
Subclass Balloon
 IS-A relationship (Generalization)
 Inheritance from a superclass to its subclass
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is-associated-with (association)
customer
isa
wholesale
order
isa (specialization)
retail
is_part-of(aggregation)
item
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What is Object-Orientation?...
 Inheritance
 A mechanism whereby classes can make use of the methods and
variables defined in all classes above them on their branch of the
class hierarchy.
 Reduce of code
 Differential Programming
 Increase of application programmer’s
Understanding capability
Productivity
Reliability
Maintainability
....
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What is Object-Orientation?...
 Multiple Inheritance
A class can have any number of superclasses.
[Example]
 Class VTOL (vertical takeoff and landing) Aircraft may have class
Airplane and class Helicopter as its superclasses.
 Class WorkingStudent can be defined as the subclass of both class
Worker and class Student
Resolving the name conflicts is a problem
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What is Object-Orientation?...
[Example]
 Both classes Worker and Student have variable “income”
representing salary and scholarship, respectively.
How do you define variable “income” in class WorkingStudent?
 Overriding
The name of a method or a variable that is lowest in the
class hierarchy takes precedence, overriding the more
general definitions further up the hierarchy.
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What is Object-Orientation?...
 Polymorphism
The ability for different objects to be able to respond to the
same message with their own unique behavior(operator
overloading)
[Example]
 anAirplane fly
aHelicopter fly
aBird fly
…
 anAudio display
aVideo display
aGraphic display
…
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Some OO DBMSs
 O2 Lecluse et al 1988
 ObjectStore (Lamb et al 1991)object design
 VersantVersant object technology
 Gemstone  Servio Corp.
 Gemstone
 ONTOS
 Objectivity DB
 Many OODB systems have been developed but vanished
soon after [Silberschatz 2006].
ODMG has defined standards for Persistent C++ and Java bu
t discontinued its activity at 2002
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ODL (Object definition language)
Object-Oriented DBMS
ODL: Object description language
Ideas
Relations
Relational DBMS
E/R
The Database modeling and implementation
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Object-Oriented DBMS
ODL
C++based OODBMS
C++ embedding
Abstract ODL
ODL Smalltlak
Smalltalk-based OODBMS
Embedding
The Database modeling and implementation
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ODL definition of class
 The keyword “interface” is used to define a class
Interface Movie {
attribute string title;
attribute integer year;
attribute integer length;
attribute enum film {color, blackandwhite} filmtype;
};
An object of type Movie could be:
(“Gone with the wind”, 1939,231, color)
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ODL definition of class…
Interface Star {
attribute string name;
attribute Struct Addr
{string street, string city} address;
};
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ODL definition of class…
Interface Movie {
attribute string title;
attribute integer year;
attribute integer length;
attribute enum film {color, blackandwhite} filmtype;
relationship Set<Star> stars inverse Star::StarredIn;
relationship Studio ownedBy inverse Studio::owns;
};
Interface Star {
attribute string name;
attribute Struct Addr
{string street, string city} address;
relationship Set<Movie> starredIn inverse Movie::stars;
};
Interface Studio {
attribute string name;
attribute string address;
relationship Set<Movie> owns
inverse Movie::ownedBy;
};
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ODL..
 Suppose we like to define a relation from Movie to star:
ralationship Set<star> stars; //stars is the relation name
(defined within the interface Movie; Movie has a set of Stars)
 Inverse relation (from stars to Movie): in the Star interface
ralationship Set<Movie> starredIn; //starredIn is the relation name
 Define a relation and its inverse
ralationship Set<Movie> starredIn InverseMovie::stars;
 Subclass definition and hence inheritance
interface Cartoon: Movie{
ralationship Set<star> voices;
 Multiple inheritance is possible, for example from cartoon and murder-mystry
interface cartoon-murder-mystry: cartoon, murder-mystry {};
 Keys may be defined as:
interface Movie (Key(title,year)){….}
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Subclass/Superclass
 Consider Subclasses of Movie
 Cartoon
 Murder mysteries
 Adventure
 Comedies
Interface Cartoon : Movie {
relationship Set <Star> voices;
};
A subclass inherits all properties of its superclass
Hierarchy of subclass relationship is possible
Multiple inheritance:
Interface Cartoon-MurderMystery: Cartoon, MurderMystery{};
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OQL
 OQL: An extension on object-oriented language like smallt
alk, Java.
 Some example: asking the year of the movie…
SELECT m.year
FROM Movies m
WHERE m.title=“Gone with the wind”
 Asking names of stars of Casablanca
SELECT s.year
FROM Movies m, m.stars s
WHERE m.title=“Casablanca”
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OQL…
 Asking the names of movies of Disney (eliminate duplicate
s)
SELECT DISTINCT s.name
FROM Movies m, m.stars s
WHERE m.ownedBy.name=“Disney”
 Asking the set of pairs of stars living at the same address.
By using s1.name<s2.name duplicate pairs are not
produced.
SELECT DISTINCT Struct(star1: s1, star2: s2)
FROM Stars s1, Stars s2
WHERE s1.addr = s2.addr AND s1.name < s2.name
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OQL…
 ORDER BY
 FOR ALL x IN S : C(x)
 EXISTS x in S :C(x)
 AVG
 GROUP BY
 SUM
 HAVING
 UNION
 INTERSWCT
 EXCEPT
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OQL…
Keys:
 A set k of one or more attributes
 No two objects can have the same key
Interface Movie
(key (title, year))
{
.
.
}:
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OODB Implementation
 OO Programming Languages +
 Object Persistencey: Objects of an OO program (like variables of a
structured program) vanish as the program is completed. These
programming languages must be extended to handle persistent data.
There are several methods to do this.
Persistent by class: declare the class as persistent then all objects
of the class are persistent.
Persistent by creation: provide a syntax for introducing objects as
persistent. Some objects are transient while others are persistent.
Persistent by reachability: One or more objects are declared as
root persistent objects. All other objects are persistent iff they are
reachable from roots.
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OODB Implementation…
 Persistent pointers: must be able to define persistent pointers. Must
be able to fetch objects from disk and return an in-memory pointer.
 Relationship: are represented by storing pointers from each object
to the objects that is related to. If b points to c then an automatic
pointer will be created from c to b.
 Iterator interface: an interface is required to iterate over members
of a class
 Transactions: Support of starting and ending transactions.
 Updates: Updates to the database should be transparent. Therefore
same functions can be used to update objects regardless of whether
they are persistent or transient.
 Query Languages: is needed
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Disadvantages of OODBMS
 No Standard
 No query language
 Too many object classes since each object can only be a m
ember of one object class
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Integrity rules &Constraints
 Candid Key: An attribute or a set of attributes which
u
niquely identifies objects
 Attributes composing can. Key: May not be Null or default
values
 Referential integrity:
 if a pointer points to an object the object must exists
 During deleting an object make sure no other object points to this
object
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