Object Oriented Databases

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Concept of the Databases

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Introduction to Database

Rational database frameworks bolster a little accumulation of information sorts (whole numbers, dates, string, singe), which has demonstrated satisfactory for customary applications, for example, authoritative information handling. In numerous application spaces in any case, substantially more mind boggling sorts of information must be dealt with. Cases of areas with complex information incorporate PC Aided outline (CAD/CAM), interactive media vaults and report administration. These information are put away in OS document frameworks or specific information structures as opposed to in a DBMS. To bolster such applications, a DBMS must bolster complex information sorts. Question arranged ideas emphatically affected endeavors to upgrade database bolster for complex information and prompted to the improvement of protest situated frameworks.

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The question situated frameworks have created along two particular ways;

Object-situated Database Systems: these are proposed as an other option to social frameworks and are gone for application spaces where complex items assume a focal part. The approach is vigorously affected by protest arranged programming dialects and can be comprehended as an endeavor to add DBMS usefulness to a programming dialect condition. The Object Database Management Group (ODMG) has built up a standard Object Data Model (ODM) and Object Query Language (OQL), which are what might as well be called the SQL standard for social database frameworks.

Object-Relational Database Systems: This can be considered as an endeavor to broaden social database frameworks with the usefulness important to bolster a more extensive class of utilizations and from multiple points of view give a scaffold between the social and protest situated worldview. The SQL: 1999 standard stretches out SQL to join bolster for the Object social model of information.

Object orientation

Object orientation is a demonstrating and advancement strategy in view of question situated (OO) ideas. It is an arrangement of outline and advancement standards in view of PC structures called objects. Each protest speaks to a genuine element with the capacity to follow up on itself and cooperate with different items. OO ideas originate from protest arranged programming (OOP) which was produced as a contrasting option to customary programming strategies. OOP ideas initially showed up in Ada, ALGOL, LISP, SIMULA which set the phase for the presentation of more refined OO ideas. Smalltalk, C++ and Java are more well known OOPLs.

Question Oriented Concepts

Objects: Components and Characteristics

In OO frameworks all that we manage is a protest eg. Understudy, receipt, plane, worker, a report and so forth. An Object is a dynamic portrayal of true substance that has remarkable character, installed properties and the capacity to interface with different protests and follow up on itself.

Object Identity

Question personality is one of a kind character for every autonomous protest put away in the database. It is spoken to by a question ID (OID) which is one of a kind to each protest and is alloted by the framework right now of the protest creation. The OID can't be changed under any conditions.

Contrast between Primary key with an OID

As opposed to OID an essential key depends on client given estimations of chose properties and can be changed whenever. The OID is doled out by the framework, does not rely on upon the items quality values and can't be changed. The OID can be erased just if the protest is erased, and that OID can never be reused.

Attributes (Instance factors)

Items are depicted by their qualities known as example factors in an OO domain. Each property has a remarkable name and an information sort related with it. Traits additionally have an area. Space consistently assembles and portrays the arrangement of every single conceivable esteem that a characteristic can have.

Object state

The question state is the arrangement of qualities that items' characteristics have at a given time. Despite the fact that the protest's state can shift, its OID continues as before. In the event that we need to change the articles state, we should change the estimations of the items qualities. To change the articles characteristic qualities, we should make an impression on the protest. The message will summon a technique.

Messages and Methods

A strategy is the code that plays out a particular operation on the items information. Techniques shield information from immediate and unapproved access by different items.

object

Each operation performed on a protest must be executed by a strategy. Strategies are utilized to change the items ascribe values or to give back the estimation of chose question traits. Techniques speak to genuine activities, for example, changing an understudies' major, adding an understudy to a course, or printing an understudy name and address. Techniques are what might as well be called methodology in customary programming dialects. In OO terms, techniques speak to the articles' conduct.

Each strategy has a name and a body. The body is made out of PC guidelines written in some programming dialect to speak to a certifiable activity. E.g. to get the region of a circle we can characterize a technique getArea() that will give back the territory of a circle.

To summon a strategy, a message is sent to the question. A message is sent by indicating a recipient question, the name of the technique and any required parameters. The inner structure of the protest can't be gotten to straightforwardly by the message sender (another question). The capacity to conceal the articles interior points of interest (qualities and strategies) is known as epitome.

Classes

OO frameworks characterize objects as per their likenesses and contrasts. Objects that share basic attributes are gathered into classes. A class is an accumulation of comparable articles with shared structure (qualities) and conduct (strategies). It contains the portrayal of the information structure and techniques usage points of interest. Each protest in a class is known as class occasion or question example.

Illustration: we can have a class named understudy to store understudy objects. Understudy objects have a similar structure (properties) and react to similar messages (actualized by strategies). E ach occurrence of a class is a question with remarkable OID and each protest knows to which class it has a place.

public student {
private int RegNo;
private  String Name;
private  String CourseTaken;
private  int grade;
Public student (String name, int RegNO){
this.name=name;
this.RegNO =RegNO;
}
public int averageGrade(){
return grade;
}
Public enroll(){
return courseTaken;
}
}

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Class chain of importance: superclass, Subclass and Inheritance

Classes are sorted out into class progression. A class chain of importance takes after a topsy turvy tree in which each class has just a single root or parent class. Class arranges objects into gatherings of items that share regular qualities. E.g. class Vehicle incorporates autos and trucks. Melodic instruments incorporates stringed and wind instruments. In the main illustration, class Vehicle is a superclass while the classes' auto and truck are subclasses.

Legacy is the capacity of a protest inside a pecking order to acquire the information structure and conduct (techniques) of the classes above it. Eg. the class auto acquires its information structure and strategies from the superclass vehicle. It is through legacy that OO frameworks convey code reusability. The superclass technique definition might be superseded by characterizing new strategies in the subclass level

Abstract Data Types (ADT)

An information sort portrays an arrangement of items with comparable qualities. The arrangement of predefined base information sorts incorporate genuine, whole number, string, singe which are liable to predefined set of operations. ADT depicts an arrangement of comparative items. ADT contrasts from routine information sorts in that:

  • ADT operations are client characterized
  • ADT epitomizes its definition, along these lines concealing its qualities

To make theoretical information sort the accompanying must be characterized:

  • Name (protest name)
  • Data portrayal or example factors of the items having a place with unique information sort
  • ADT operations and imperatives, both of which are actualized through techniques

ADT together with legacy offer help for complex items. A mind boggling item is framed by consolidating different questions in an arrangement of complex relations. Illustration: a security framework that utilizations diverse information sorts, for example,

  • Conventional (forbidden) worker information: name, telephone, DOB
  • Bitmap information to store worker picture
  • Voice information to store the worker voice design
  • Attributes of Object arranged information demonstrate (OODM)

The protest situated ideas speaks to the center attributes of a question arranged information display (OODM) otherwise called question information demonstrate (ODM). A question arranged information display must:

  • ADT operations are client characterized
  • ADT epitomizes its definition, along these lines concealing its qualities
  • To make theoretical information sort the accompanying must be characterized:
  • Name (protest name)
  • Data portrayal or example factors of the items having a place with unique information sort
  • ADT operations and imperatives, both of which are actualized through techniques
  • ADT together with legacy offer help for complex items. A mind boggling item is framed by consolidating different questions in an arrangement of complex relations. Illustration: a security framework that utilizations diverse information sorts, for example,
  • Conventional (forbidden) worker information: name, telephone, DOB
  • Bitmap information to store worker picture
  • Voice information to store the worker voice design
  • Attributes of Object arranged information demonstrate (OODM)
  • The protest situated ideas speaks to the center attributes of a question arranged information display (OODM) otherwise called question information demonstrate (ODM). A question arranged information display must:
  • Support portrayal of complex articles
  • Be extensible i.e. must be fit for characterizing new information sorts and also the operations to be performed on them
  • Support epitome i.e. the information portrayal and the techniques execution must be avoided outer substances
  • Exhibit legacy: a protest must have the capacity to acquire the properties (information and techniques) of different articles
  • Support the thought of question character (OID)

Fundamental Components of an OODM

  • The OODM models certifiable substances as articles
  • Each question is made out of qualities and an arrangement of techniques
  • Each trait can reference another protest or an arrangement of articles
  • The traits and strategies usage are shrouded (embodied) from different articles
  • Each protest is recognized by a novel question ID (OID), which is autonomous of the estimation of its properties
  • Similar articles are portrayed and gathered into a class that contains the depiction of the information (qualities and techniques) and usage
  • The class depicts a kind of question
  • Classes are sorted out in a class progressive system
  • Each question of a class acquires all properties of its superclasses in the class chain of importance

Comparing OO Data model and ER model

Likenesses and distinction amongst OODM and Previous information modelsIn spite of the fact that the OODM has much in the same way as social or ER information models, it presents some major contrasts as takes after:

Object, substance and Tuple

The OODM idea of question amplifies well past the idea of element or tuple in other information models. Regardless of the possibility that OODM question looks like the substance and the tuple in the ER and social models, an OODM protest has extra qualities, for example, conduct, legacy and exemplification.

Class, element set and table

The idea of class can be related with the ER and social models ideas of element set and table individually. In any case, class is an all the more effective idea that permits the depiction of the information structure as well as the portrayal of conduct of the class objects. A class likewise takes into consideration both the idea and execution of dynamic information sorts (ADT). ADT permits the client to make new information sorts and utilize them like some other base information sorts.

Encapsulation and Inheritance

ADT brings two other OO highlights that are not bolstered in past models: epitome and legacy. Classes are sorted out in class progressive systems. A question having a place with a class acquires every one of the properties of its super-classes. Epitome implies that the information portrayal and different techniques usage are avoided different items and from the end client. In OODM, no one but strategies can get to the case factors. In customary models, information parts or fields are straightforwardly open from outside condition.

Customary models don't consolidate the strategies found in OO frameworks. The nearest is the utilization of triggers and put away techniques in SQL databases. Be that as it may, in light of the fact that triggers do exclude legacy and exemplification, they don't yield an indistinguishable usefulness from techniques.

Relationships

The principle property of any information model is found in its portrayal of connections among the information parts. The connections in an OODM can be of two sorts: interclass references or class progressive system legacy. The OODM utilize the IOD which is character based to set up connections among articles and such connections are free of the condition of the protest. The ER and social models utilize esteem based relationship approach i.e, relationship among substances is built up through a typical incentive in one or a few of the element traits.

Access techniques

The ER and social models rely on upon the utilization of SQL to recover information from the database. SQL is a set-situated inquiry dialect that depends on scientific model. The OODM utilize Object Query Language (OQL)

Question situated Database administration frameworks (OODBMS)

The OODBMS is a database administration framework that incorporates the advantages of regular database frameworks with the all the more capable demonstrating and computational qualities of the protest situated information show.

object Features

OODBMS products are used to develop complex systems such as:

  • Medical applications that handles digitized data such as X-rays, MRI scans and Ultra sounds
  • Financial applications in portifolio and risk management. Such applications yield a real time view of data that is based on multiple computations and aggregation applied to data that are acquired from complex stock transactions over the world.
  • Telecommunications applications such as network configuration management applications that automatically monitor track and reconfigure communication networks based on multiple parameters in real time.
  • Computer-aided design (CAD) and Computer-aided Manufacturing (CAM)
  • Multimedia applications, eg GIS, that use video, sound and high quality graphic that require specialized data management features such as intersect, line, point, polygon etc.

Examples:

Commercial: Versant, ObjectDB, Mongo, Gemstone, VOSS, Mercury etc
Open source: db4o, EyeDB, NeoDatis ODB, Ozone, Perst and Zope(ZODB)

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Features of an OODBMS

An OODBMS is the result of combining OO features such as class inheritance, encapsulation and polymorphism with database features such as data integrity, security, persistence, transaction management, concurrency control, backup, recovery and system tunning. The “Object oriented Database System Manifesto” (Atkinson et al.,1989) was the first to define OODBMS features and included 13 Mandatory features as well as optional characteristics of the OODBMS. The rules are divided into two sets: Eight characterize OO system and Five characterize a DBMS.

Thirteen OODBMS Rules

SET 1: Rules that make it OO System

  1. The system must support complex objects
  2. Object identity must be supported
  3. Objects must be encapsulated
  4. The system must support types or classes
  5. The system must support inheritance
  6. The system must avoid premature binding
  7. The system must be computationally complete
  8. The system must be extensible

SET 2: Rules that make it DBMS

  • The system must remember data locations
  • System must be able to manage very large databases
  • The system must accept concurrent users
  • The system must be able to recover from hardware and software failures
  • The system must be simple

OODBMS: Advantages and Disadvantages

Compared to RDBMS market share, OODBMS have a long way to go before they can claim double digit market percentage.  Part of OODBMS lack of market acceptance is the RDBMS has incorporated many OO features while retaining its conceptual simplicity, thus diminishing the need of OODBMS.  Most of the benefits expressed by OODBMS are in terms of Complex object management capabilities. OODBMS rely on OOPL to achieve this.

Advantages

  • One data model
  • OODBMS provide an edge in the support for complex objects which makes desirable for use in specialized application areas.
  • Permit the extensibility of base data types, thereby increasing both the database functionality and its modeling capability.
  • Provides dramatic performance improvement compared to RDBMS when managing complex data.
  • Reusability of classes allows for faster development and easier maintenance of the database and its applications
  • Full support for object-orientation including class hierarchies and inheritance

Disadvantages

  • Information abstraction
  • Design and development tools
  • Query support including optimization
  • In terms of theory and implementation, OODBMS much more challenging than RDBMS as they support more complex data and functionality
  • challenges of how best to store and cluster objects
  • challenges of how to seamlessly integrate querying into procedural languages
  • Difficult to succeed in marketplace against established DBMS Companies. Tend to be addressing specific markets
  • very large-scale databases with complex data objects
  • business domains such as e-publishing
  • embedded databases

Example: Creating and storing objects Using db40

Simple example of creating and storing, querying, updating , deleting person objects assume a normal  Person class

public Person {
private String name;
private int age;
public Person(String name, int age) {
this.name = name;
this.age = age;
}
public int getAge() {
return age;
}
public String getName() {
return name;
}
...
}

Accessing a Database

ƒ db4o database is an ObjectContainer associated with a specific  disc file

ObjectContainer db = Db4o.openFile();
try {
// access db
}
finally {
db.close();
}

Creating and Storing Objects

ƒ Create objects as usual and then make them persistent using the set() method on the database
Person p1 = new Person("Fred Kimani", 35);
db.set(p1);
Person p2 = new Person("Mary Jones", 24);
db.set(p2);

Querying Objects

One option to locate objects is a Query by Example (QBE) approach.ƒCreate a prototypical object that specifies properties of desired objects
// retrieve by age (null default for string)
Person proto = new Person(null, 35);
ObjectSet result = db.get(proto);
// retrieve by name (0 default for int)
Person proto = new Person("Mary Jones", 0);
ObjectSet result = db.get(proto);
// shortcut to retrieve all persons
ObjectSet result = db.get(Person.class);

Updating Objects

ƒ First retrieve object (or objects), then perform update and then store
// update age of person
// assumes single result to query
ObjectSet res = db.get(new Person("Mary Jones", 0);
Person p = res.next();
p.setAge(40);
db.set(p);
ƒ Note that the get() and set() methods must be done as two separate stages so prototype object first used to identify existing object to be updated and then that known object is updated.

Deleting Objects

ƒ As with updating objects, objects must first be retrieved and then deleted
// delete Fred Bloggs from database
ObjectSet res = db.get(new Person("Fred Kimani", 0);
Person p = res.next();
db.delete(p);public Person {
private String name;
private int age;
public Person(String name, int age) {
this.name = name;
this.age = age;
}
public int getAge() {
return age;
}
public String getName() {
return name;
}
...
}

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