Object Database Systems

8/12/2019 Object Database Systems

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23 July 2014 16.OBJECT-DATABASE SYSTEMS/D.S JAGLI


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Introduction1. Relational database systems support a small, fixed

collection of data types (e.g., integers, dates, strings),which has proven adequate for traditionalapplication domains

Eg: administrative data processing.

2. In many application domains, much more complex

kinds of data must be handled.3. Typically this complex data has been stored in OS file

systems or specialized data structures, rather than ina DBMS.



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Introduction

Why OODBMS?

Let us start with modeling this simple example in a

RDBMS Assume that we are given the following diagram

0,0

1

2

34

5

6 7

8



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Introduction

Motivating Example Our objective is to store this graph in a RDBMS and

support queries on these simple geometries What kind of relations we need?

Print names of rectangles which are squares

Find all objects which are inside the rectangle 7.

0,0

1

2

34

5

67

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Introduction

Motivating Example Relations

POINT(pname, x, y), EDGE(ename, aPoint), RECTANGLE(rname,anEdge).

0,0

1

2

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5

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8

r5 e1

r5 e2

r5 e3

r5 e4

e1 p1

e1 p2

e2 p2

e2 p3

e3 p3

e3 p4

e4 p4

e4 p1

p1 3 4

p2 3 10

p3 10 10

p4 10 4

RECTANGLE

EDGEPOINT



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Introduction

Though we can model and query these simplegeometric objects, its Not clean

Complexity increases with complex objects (like irregularpolygons)

Even with these simple objects, how do you answer querieslike find nearest objects to point 2 or find all intersectingobjects

What is lacking Support for complex data types

Support for predicates (e.g., area, intersect, length)



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Relational Databases Traditionally, could not represent files such as

pictures, audio and video natively (only BLOB)



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Features offered by a DBMS1. reduced application development time,2. concurrency control and recovery,

3. indexing

4. support, andquery capabilities Are increasingly attractive and, ultimately,

necessary.

In order to support multimedia applications, a DBMSmust support complex data types.

Object-oriented concepts have strongly influencedefforts to enhance database support for complex dataand have led to the development of object-databasesystems,



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Object-database systems have developed along two distinctpaths:

Object-oriented database systems: Object-orienteddatabase complex objects play a central role. The approach isheavily influenced by object-oriented programming languagesand can be understood as an attempt to add DBMSfunctionality to a programming language environment.

Object-relational database systems: Object-relationaldatabase systems can be thought of as an attempt to extendrelational database systems with the functionality necessary to

support a broader class of applications and, in many ways,provide a bridge between the relational and object-orientedparadigms.



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OODBMS: A Solution? Started in the 1980s

Integrates database capabilities with OO programminglanguage capabilities

Makes database objects appear as programminglanguage objects in an existing language (such as JAVA,C++ or Smalltalk)

Relational Model is no longer valid: objects are relatedthrough inheritance and polymorphism

More of a persistent programming language than aDBMS



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OO Advantages OO principles brought to databases:

New modeling power

Extensibility of systems Code reuse

Easy maintenance of programs

However, it is only recently that OO programming has

itself really taken off.



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The drawbacks No clear standard

(ODMG did come up with one, but it was not accepted by themajor OODBMS vendors)

Lack of interoperability with traditional RDBMS tools(such as OLAP, backup and recovery, reporting, etc)

Seen by some as a lost opportunity to revolutionizesoftware and database development

Today, there are more products that perform object-sqlmaping than there are pure OODBMS



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Relational Database (revisited) Represents data in a table

Think of displaying this information in a spreadsheet

Requires indexing and sorting which takes time SQL may not be able to get the information we need in

a complex query



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DefinitionsFrom Stonebraker: Object-Relational DBMSs: TheNext Great Wave

Filesystems: no query

RDBMS: query, simple data

ODBMS: no (poor) query,complex data

ORDBMS: query & complex (Picture Akmal Chaudri)



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OODBMS Terminology Object Identity:An object is denoted in a unique way

in the database system, using an identifier or OID(object identifier) that the objects keeps during itsentire lifetime, independently of its attribute values.



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OODBMS Terminology Type: the type of an object corresponds to its

structure and to the operations that can be

performed on it. Atomic types, such as strings and integer

Complex types are defined using constructors (tuplesor set constructors).

An object (o) can have as an atomic value not onlya string or real but also the OID of another objecto. Object o is said to consist of object o



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OODBMS Terminology Objects with the same type are grouped into classes.

Classes encompass objects having the same structure

and behaviour, which is expressed by the set ofmethods or operations applicable to the objects theycontain.



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OODBMS TerminologyADTs:Abstract data types combinations of data

types (e.g., polygon) and their operations (e.g.,PolygonArea [an operation that would compute

the area of a polygon]). Note that the DBMS neednot have any knowledge on the ADTimplementation (i.e., the code corresponding tothe operations).

ADTs are encapsulated in the sense that they areaccessible only through the operations that aredefined on them.



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ADTs have been regularized in the sense that thegeographic dimension (e.g., points, line segments[nodes only have two arcs], complex polylines [nodescan have two or more connected arcs], polygons) isused to clearly distinguish between them.



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OODBMS Terminology Inheritance: Subclasses are defined from an existing

superclass with a refinement of its structure. Subclasses inherit methods and structures from the superclass (e.g.,

all methods defined for the superclass can be used in the subclass).

However, a subclass can redefine a method defined in thesuperclass.

A subclass can also have methods defined only for that subclass.This leads to polymorphism.

The subclass is a specialization of the superclass, and thesuperclass is a generalization of the subclass.

A subclass can inherit from many superclasses.



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OODBMS Terminology Most OO DBMS use OQL rather than SQL as their

query language.

OQL is aware of the complex structures present inthe OODBMS, and can return complex results.

SQL is used as the DDL, DQL and DML (datadefinition, data query, and data manipulationlanguage).

In OODBMS, the primary means of developing thedatabase is through the native OO language.



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object-oriented database management

systems (OODBMSs)

The data in object-oriented database managementsystems (OODBMSs) is managed through two sets ofrelations, one describing the interrelations of dataitems and another describing the abstract

relationships (inheritance).



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systems (OODBMSs) The strong connection between application and

database results in less code, more natural datastructures, and better maintainability and reusability

of code. OO languages, such as C++ or Java, are able toreduce code size by not having to translate code into adatabase sublanguage such as SQL and ODBC or JDBC.



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New Data Types User-dened abstract data types (ADTs):

Structured types:

Inheritance:



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The rich variety of data types in an ORDBMS oers adatabase designer many opportunities

for a more natural or more effcient design.



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differences between RDBMS and

ORDBMS database design Structured Types and ADTs



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Introduction to Object-Relational DBMSs Several major software companies including IBM,

Informix, Microsoft, Oracle, and Sybase have allreleased object-relational versions of their products.

These companies are promoting a new, extendedversion of relational database technology calledobject-relational database management systemsalso known as ORDBMSs.



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Does a database supporting complex applications have to be

object-oriented?

A certain group thinks that future applications canonly be implemented with pure object-orientedsystems. Initially these systems looked promising.

However, they have been unable to live up to theexpectations.

A new technology has evolved in which relationaland object-oriented concepts have been combined

or merged. These systems are called object-relational database systems.

The main advantages of ORDBMSs are massivescalability and support for object-oriented

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Advantages of ORDBMSs The main advantages of extending the relational

data model come from reuseand sharing.

Reuse comes from the ability to extend the DBMSserver to perform standard functionality centrally,rather than have it coded in each application.

If we can embed the functionality in the server, itsaves having to define it in each application thatneeds it, and consequently allows the functionalityto be shared by all applications.



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Disadvantages of ORDBMSs The ORDBMSs approach has the obvious disadvantage of

complexity and associated increased costs.

There are proponents of the relational approach thatbelieve the essential simplicity and purity of the relationalmodel are lost with these types of extension.

There are also those that believe that the RDMSs is beingextended for what will be a minority of applications that donot achieve optimal performance with current relationaltechnology.



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Disadvantages of ORDBMSs (Cont.) Instead of discussing object models, terms like user-

defined data types are used. The terminology of object-orientation abounds with terms like abstract types. classhierarchies, and object models. However, ORDBMSs

vendors are attempting to portray object models asextensions to the relational model with some additionalcomplexities.

This potentially misses the point of object-orientation,

highlighting the large semantic gap between these twotechnologies.



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Relational DBMS The relational model was formally introduced by

Dr. E. F. Codd in 1970 and has evolved since then,through a series of writings and later throughimplementations by IBM and others. The definingstandard for relational databases is published by

ANSI (the American National Standard Institute)

as SQL (ANSI 1986) or SQL1, called SQL-86. Arevised standard is called SQL2, also referred to asSQL-92.



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Relational DBMSA relational database is composed of many

relations in the form of two-dimensional tables ofrows and columns containing related tuples.

Organizing data into tables, the form in whichdata is presented to the user and the programmer,is known as the logical viewof the database. The

stored data on a computer disk system is called theinternal view. The rows (tuples) are calledrecordsand the columns (fields in the record) arecalled attributes.



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RDBMSs RDBMSs use Structured Query Language (SQL,

currently SQL2) as the data definition language(DDL) and the data manipulation language(DML).

SQL includes statements for data definition,modification, querying and constraint

specification. The types of queries vary fromsimple single-table queries to complicated multi-table queries involving joins, nesting, setunion/differences, and others.



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disadvantages of Relational DatabasesAll processing is based on values in fields of

records. Examples of RDBMSs include Oracle,developed by Oracle Corporation, and Microsoft

Access developed by Microsoft.

The main disadvantages of Relational Databasesinclude their inability to handle application areaslike spatial databases (e.g. CAD), applicationsinvolving images, special types databases (e.g.complex numbers, arrays, etc.) and otherapplications that involve complexinterrelationships of data.



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Object-Oriented DBMS (OODBMS)

The concept of abstract data types (ADTs) inwhich the internal data structure is hidden and the

external operations can be applied on the objectthat is specified led to the concept ofencapsulation.

The programming language SMALLTALK,developed by Xerox, was designed to be object-oriented. Other object-oriented programminglanguages include C++, Java, etc.



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Object-Oriented DBMS (OODBMS) The main features of OO programming languages are

encapsulation, inheritance and polymorphism.

Encapsulation can be thought as a protective layerthat prevents the code and the data from beingaccessed by other code defined outside the layer.



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Object-Oriented DBMS (OODBMS)

The process in which one object inherits theproperties of a previously defined object is calledinheritance. Inheritance aids in the reuse ofexisting definitions for creating new objects.

Polymorphism allows the same operator orsymbol to have different implementations,depending on the type of objects to which theoperator is applied.



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systems (OODBMSs)

The data in object-oriented database managementsystems (OODBMSs) is managed through two sets ofrelations, one describing the interrelations of dataitems and another describing the abstract

relationships (inheritance).



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systems (OODBMSs) The strong connection between application and

database results in less code, more natural datastructures, and better maintainability and reusability

of code. OO languages, such as C++ or Java, are able toreduce code size by not having to translate code into adatabase sublanguage such as SQL and ODBC orJDBC.



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Changing the lack of defining the lack of a defining standard was a drawback for

OODBMSs.

The Object Data Management Group (ODMG) hasproposed a standard known as ODMG-93 or ODMG1.0 standard , now revised into ODMG 2.0.



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Consists The standard consists of the object model, the object

defining language (ODL), the object query language(OQL), and the bindings to OO programming

languages.

The ODL and OQL are based on the ODMG data

model.



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Data Model The data model consists of data types, type

constructors, etc., and is similar to the SQL reportthat describes the standard model for relationaldatabases.

The ODL is designed so as to support semantic

constructs of ODMG 2.0 object model. It isindependent of any programming language. TheODL is used to create object specifications.



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Data Model (cont.) The OQL is designed to work closely with the

programming languages for which an ODMGbinding is defined such as C++, Java and

SMALLTALK.

The syntax of the OQL queries is similar to thesyntax of SQL (a query language for relationaldatabases) with some additional features such asobject identity, complex objects, inheritance,polymorphism and relationships.



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OODBMSsAn object-oriented language is the language for both

the application and the database. OODBMSs havebeen integrated with C++, C, Java and LISP.

The primary interface in an OODBMS for creating andmodifying objects is directly via the object language(C++, Java, etc.) using the native language syntax.



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Difference between relational databases

and OO databases The difference between relational databases and

OO databases is the way in which relationships arehandled.

In OO databases, the relationships are representedwith OIDs, which improves the data accessperformance.

In relational databases, relationships among tuplesare specified by attributes having the samedomain.



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OODBMSs Problems The main drawback of OODBMSs has been poor

performance. Unlike RDBMSs, query optimizationfor OODBMs is highly complex.

OODBMSs also suffer from problems of scalability,and are unable to support large-scale systems.Some examples of OODBMSs are O2 (now called

Ardent) developed by Ardent Software, and theObjectStore system produced by Object DesignInc.



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Object-Relational DBMS (ORDBMS)An ORDBMS supports an extended form of SQL

called SQL3 that is still in the development stages.The extensions are needed because ORDBMSs

have to support ADT's.

The ORDBMS has the relational model in itbecause the data is stored in the form of tableshaving rows and columns and SQL is used as thequery language and the result of a query is alsotable or tuples (rows).



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characteristics of an ORDBMSs Base datatype extension,

Support complex objects, Inheritance, and



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Users define datatypes

Object-Relational Database Management Systems(ORDBMSs) allow users to define data types, functionsand operators.

As a result, the functionality of the ORDBMSsincreases along with their performance.



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An example schema of a student relation

which ORDBMS supports

STUDENT(fname,lname,ID,sex,major,address,dname,location,picture)

Notice : extra attributes "location" and "picture"which are not present in the traditionalEMPLOYEE relation of RDBMS. The datatype of

"location" is "geographic point" and "picture" is"image".



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The differencesbetween the three approaches

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Criteria RDBMS ODBMS ORDBMSDefining standard SQL2 ODMG-2.0 SQL3 (in process)

Support for object-

oriented featuresDoes not support;

It is difficult to mapprogram object to the

database

Supports extensively Limited support;mostly to new data

type

Usage Easy to use OK for programmers;some SQL access for

end users

Easy to use except for

some extensions

Support for complex

relationshipsDoes not support

abstract datatypesSupports a wide

variety of datatypes

and data with complex

inter-relationships

Supports Abstract

datatypes and complex

relationships

Performance Very good

performance

Relatively less

performanc

Expected to perform

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The differences between the three

approachesCriteria RDBMS ODBMS ORDBMS

Product maturity Relatively old and so verymature

This concept is few yearsold and so relatively maturfeature

Still in development stageso immature

The use of SQL Extensive supports SQL OQL is similar to SQL, butwith additional features like

Complex objects andobject-oriented features

SQL3 is being developedwith OO features

incorporated in it

Advantages Its dependence on SQL,relatively simple queryoptimization hence goodperformance

It can handle all types ofcomplex applications,reusability of code, lesscoding

Ability to query complexapplications and ability tohandle large and complexapplications

Disadvantage Inability to handle complexapplications

Low performance due tocomplex query optimization,

inability to support large-scale systems

Low performance in webapplication

Support from vendors It is considered to behighly successful so themarket size is very largebut many vendors aremoving towards ORDBMS

Presently lacking vendorsupport due to vast size ofRDBMS market

All major RDBMS vendorsare after this so has verygood future

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