DBMS Bascis

DataBase Systems

Ch. Venkata Rami ReddyCS-222 II-II SEM

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UNIT – I

• Database System- concepts and architecture,

Data modelling using the Entity Relationship (ER) modelling and Enhanced Entity Relationship (EER) modelling, Specialization and Generalization.

Venkata Rami Reddy Ch Dept of CSE

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UNIT-1

• Understanding the DBMS basic concepts• Know the Applications of DBMS. • To know the Database Designing for the real time

applications by using ER and EER models.• To understanding the Specialization and

GeneralizationObjectives:


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UNIT-1

Outcomes::


• Students will able to know the DBMS concepts and their importance.

• Students will able to design the databases for any real time applications.

• Students will the constraints to be considered while designing the databases

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UNIT-1

Topics::


1. Introduction to Database Systems2. File System3. Advantages of DBMS4. DBA, Designers and End users5. Data Models

• Relational Model• Entity-Relationship Model• Hierarchical Model• Network Model• Object-Oriented Model

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Contents 6. Levels of Abstraction or Three-Schema

architecture7. DBMS architecture8. CLASSIFICATION OF DATABASE

MANAGEMENT SYSTEMS9. Phases of Database Design

Topics:


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Contents

Topics:


10. Entity-Relationship model• Types of Attributes• Entity Types and Entity Sets:• Notations of ER Diagrams• Example Database Application• Relationship:• Degree of a Relationship Type• Constraints on Relationships

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Contents

Topics:


11. EER (Enhanced Entity Relationship) Model

• SUBCLASSES, SUPERCLASSES AND INHERITANCE

• Specialization

• Generalization

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• A data mean known facts or raw facts that can be recorded and that have implicit meaning.

• For example, consider the names, telephone, numbers, and addresses of the people you know. You may have recorded this data in an indexed address book, you may have stored it on a hard drive, using a personal computer and software such as Microsoft Access, or Excel.

• Information: Processed data.

Topic

Introduction to Database Systems

1

data


Introduction to Dbms

in

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• Database is a large collection of related data that can be stored generally describes activities of an organization.Topic


1

Database


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• It is used to store data of an organization.• A database is designed and developed for a

specific purpose.• It has some source from which data is derived and

it is populated with that data.• It can be of any size• It allows multiple users to share and access

database at the same time.Eg: - University database which includes students,

faculty, courses & class rooms information along with activities such as enrolment and teaching courses.

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1

Database Properties


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• A database management system (DBMS) is a collection of programs (software) for defining, creating, manipulating and maintaining a database.

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Database Management System


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• The DBMS is a general-purpose software package that facilitates the processes of defining, constructing, manipulating, and sharing databases among various users and applications.

.

Topic


1

Database Management System


Purpose of DBMS

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• Defining a database involves specifying the data types, structures, and constraints for the data to be stored in the database

• Manipulating a database includes functions such as querying the database to retrieve specific data, updating the database to reflect changes,, and generating reports from the data

• Constructing the database is the process of storing the data itself on some storage medium that is controlled by the DBMS.

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Actions of DBMS


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• Sharing a database allows multiple users and programs to access the database concurrently

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1

Actions of DBMS


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Simplified database system environment


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• Banking: all transactions• Airlines: reservations, schedules• Sales: customers, products,

purchases• Online retailers: order tracking,

customized recommendations

Topic


1

Database Applications


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• Manufacturing: production, inventory, orders, supply chain

• Human resources: employee records, salaries, tax deductions

• Universities: registration, grades

Topic


1

Database Applications:


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• Before the evolution of DBMS, File Systems are used to store and manage the data.

• In File System data will be stored in individual files.

• A File is a collection of data. • Files are typically designed to meet

needs of a particular department or user group.

• Files are also typically designed to be part of a particular computer application

Topic

File System

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File System


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• In the file processing approach, each department would "own" a collection of relevant data and software applications to manipulate that data.

Topic

File System

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File processing processing system


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1. Data Redundancy and Inconsistency2. Difficulty in accessing data3. Data isolation 4. Enforcing Integrity constraints5. Atomicity problems6. Difficulty in concurrency control 7. Security Problems

Topic 2

Drawbacks of File System


File System

Dis advantages of Filesystem

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• Data isolation: The data is scattered in different files and with different formats. So it is difficult to write application programs to retrieve the data.

• Enforcing Integrity constraints: Data integrity means, all the data has to obey some condition. In File System integrity constraints are set at program level.

Topic

File System

2

Cont ...


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Data Redundancy and Inconsistency: • Data redundancy means appearing same

data in different places.• In file system same information is stored at

different places it causes data-inconsistency problems during updates.

Difficulty in accessing data: • In order to retrieve data from files we need to

write special application program every time. • This is not a convenient way because every

time the requirements may change need to write a new program to carry out each new task

Topic

File System

2

Cont ...


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Atomicity problems: • Atomicity is a property of a transaction it states that

either all actions to be performed or none.• In file processing system incomplete transactions

cannot roll back. Due this data will be inconsistent. Difficulty in concurrency control:• concurrency means same file is updated by

different application programs at the same time.• In File Processing System it is not possible to

handle concurrency because of that we can get inconsistent data

Topic

File System

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Cont ...


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Security Problems:• Since the information is scattered in different files

and does not have centralized access path, so it is not possible to provide security to the data so that everyone can access the data.

Topic

File System

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Cont ...


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1. Controlling Redundancy2. Data Consistency3. Data Security4. Providing Storage Structures for Efficient Query

Processing5. Providing Backup and Recovery6. Providing concurrency control7. Enforcing Integrity constraints8. Report Writers

Topic

Advantages of DBMS

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Advantages of DBMS


DBMS Advantages

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• In non-database systems (traditional computer file processing), same data is stored in many places.

• Redundancy leads to several problems 1.duplication effort: same data can be entered multiple times 2. Storage space is wasted. 3. Data inconsistency.

• In DBMS, all the data of an organization is integrated into a single database.

• By controlling the data redundancy, you can save storage space

Topic

Advantages of DBMS

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Controlling Redundancy


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• By controlling the data redundancy, the data consistency is obtained.

• If a data item appears only once, any update to its value has to be performed only once and the updated value (new value of item) is immediately available to all users.

• If the DBMS has reduced redundancy to a minimum level, the database system enforces consistency.

• It means that when a data item appears more than once in the database and is updated, the DBMS automatically updates each occurrence of a data item in the database.

Topic

Advantages of DBMS

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Data Consistency:


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• Data security is the protection of the database from unauthorized users.

• Only the authorized persons are allowed to access the database.

• Some of the users may be allowed to access only a part of database i.e., the data that is related to them or related to their department.

• Mostly, the DBA or head of a department can access all the data in the database.

Topic

Advantages of DBMS

3

Data Security


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• Some users may be permitted only to retrieve data, whereas others are allowed to retrieve as well as to update data.

• The database access is controlled by the DBA.

• He creates the accounts of users and gives rights to access the database.

• Typically, users or group of users are given usernames protected by passwords.

• Most of the DBMSs provide the security sub-system, which the DBA uses to create accounts of users and to specify account restrictions.

Topic

Advantages of DBMS

3

Data Security


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• Database systems must provide capabilities to execute queries and updates efficiently

• Because the database is typically stored on disk, the DBMS must provide specialized data structures to speed up disk search for the desired records.

• Auxiliary files called indexes are used for this purpose. Indexes are typically based on tree data structures or hash data structures.

• DBMS supports file manager to manage the allocation of disk space for the DBMS files.

• Also it supports Buffer Manager to manage the memory buffers used for processing the database information.

Topic

Advantages of DBMS

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Providing Storage Structures for Efficient Query Processing


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• Most of the DBMSs provide the 'backup and recovery' sub-systems that automatically create the backup of data and restore data if required.

• For example, if the computer system fails in the middle (or end) of an update operation of the program, the recovery sub-system is responsible for making sure that the database is restored to the state it was in before the program started executing.

Topic

Advantages of DBMS

3

Providing Backup and Recovery


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• DBMS will support concurrency control tools for permitting multiple users or application programs to access the database concurrently, while preserving the consistency of database.

• .

Topic

Advantages of DBMS

3

Providing concurrency control


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• Integrity constraints can be applied to database so that correct data can be entered in to database.

Ex: 1. minimum balance of a account is 10002. Max marks of a subject is 100

• Most database applications have certain integrity constraints that must hold for the data.

• A DBMS should provide capabilities for defining and enforcing these constraints.

• The simplest type of integrity constraint involves specifying a data type for each data item.

Topic

Advantages of DBMS

3

Enforcing Integrity constraints


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• Most of the DBMSs provide the report writer tools used to create reports. The users can create reports very easily and quickly.

• Once a report is created, it can be used many times and it can be modified very easily.

• The created reports are also saved along with database and behave like a software component.

Topic

Advantages of DBMS

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Report Writers


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Topic

DBA, Designers and End users

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Actors of DBMS


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• The database administrator is a person having central control over data and programs accessing the data.

• DBA coordinates all the activities of the database system

• They are the users who are most familiar with the database and are responsible for creating, modifying, and maintaining its three levels.

• Database Administrator is responsible to manage the DBMS’s use and ensure that the database is functioning

• DBA is responsible for granting permission to the users of the database and stores the profile of each user in the database

Topic

Database Administrator

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Database Administrator(DBA)


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1. Installing and upgrading the database server and application tools

2. Allocating system storage and planning future storage requirements for the database system

3. Modifying the database structure, as necessary, from information given by application developers

4. Enrolling users and maintaining system security

5. Ensuring compliance with database vendor license agreement

6. Controlling and monitoring user access to the database

Topic

DBA

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Responsibilities of


https://en.wikipedia.org/wiki/Installation_(computer_programs)

https://en.wikipedia.org/wiki/Upgrade

https://en.wikipedia.org/wiki/Planning

https://en.wikipedia.org/wiki/Computer_security

https://en.wikipedia.org/wiki/License_agreement

https://en.wikipedia.org/wiki/System_Monitoring

https://en.wikipedia.org/wiki/User_(computing)

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7) Monitoring and optimizing the performance of the database

8) Planning for backup and recovery of database information

9) Maintaining archived data10) Backing up and restoring databases11) Contacting database vendor for technical support12) Generating various reports by querying from

database as per need

Topic

Responsibilities of DBA

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Responsibilities of DBA


https://en.wikipedia.org/wiki/Program_optimization

https://en.wikipedia.org/wiki/Backup

https://en.wikipedia.org/wiki/Archive

https://en.wikipedia.org/wiki/Vendor

https://en.wikipedia.org/wiki/Technical_support

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• Database designers are responsible for identifying the data to be stored in the database and for choosing appropriate structures to represent and store this data.

• These tasks are mostly undertaken before

the database is actually implemented and populated with It is the responsibility of database designers to communicate with all prospective database users in order to understand their requirements, and to come up with a design that meets these requirements.

Topic

Database Designers

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Database Designers


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• In many cases, the designers are on the staff of the DBA and may be assigned other staff responsibilities after the database design is completed.

• Database designers typically interact with each potential group of users and develop views of the database that meet the data and processing requirements of these groups.

Topic

Database Designers

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Database Designers


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• End users are the people whose jobs require access to the database for querying, updating, and generating reports; the database primarily exists for their use.

• There are several categories of end users:• Casual end users• Naive or parametric end users• Sophisticated end users• Stand-alone users

Topic

End Users

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End Users


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• Casual end users occasionally access the database, but they may need different information each time.

• They use a sophisticated database query language to specify their requests and are typically middle- or high-level managers or other occasional browsers.

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End Users

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Casual end users


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• Naive or parametric end users make up a sizable portion of database end users.

• Their main job function is querying and updating the database, using standard types of queries and updates-called canned transactions-that have been carefully programmed and tested.

• The tasks that such users perform are varied:• Bank tellers check account balances and post

withdrawals and deposits.• Reservation clerks fur airlines, hotels, and car

rental companies check availability for a given request and make reservations

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End Users

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Naive or parametric end users


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• Sophisticated end users include engineers, scientists, business analysts, and others who thoroughly familiarize themselves with the facilities of the DBMS so as to implement their applications to meet their complex requirements.

Stand-alone users• Stand-alone users maintain personal databases by

using ready-made program packages that provide easy-to-use menu-based or graphics-based interfaces.

• An example is the user of a tax package that stores a variety of personal financial data for tax purposes.

Topic

End Users

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Sophisticated end users


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• A data model is a collection of concepts that can be used to describe the structure of a database.

• Structure of a database; mean the data types, relationships, and constraints that should hold for the data. Most data models also include a set of basic operations for specifying retrievals and updates on the database.

Types of Data Models• Relational Model• Entity-Relationship Model• Hierarchical Model• Network Model• Object-Oriented Model

Topic

Data Models

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Data Models


Database Models

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• Most commonly used model is the relational model.• In this model data is organized as two-dimensional tables.• Each table is called relation.• The relational model uses a collection of tables to

represent both data and the relationships among those data. Each table has multiple columns, and each column has a unique name.

• The relational model is implemented in database where a relation is represented by a table, a tuple is represented by a row, and an attribute is represented by a column of the table.

Topic

Types of Data Models

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Relational Model


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• Entity-Relationship model is based on the notion of real world entities and relationship among them.

• ER Model is best used for the conceptual design of database.

• ER Model is based on:• Entities and their attributes• Relationships among entities

Topic


5

Entity-Relationship Model


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Entity• An entity in ER Model is real world entity, which has some

properties called attributes. Every attribute is defined by its set of values, called domain.

• For example, in a school database, a student is considered as an entity. Student has various attributes like name, age and class etc.

Topic


5

Entity-Relationship Model


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• A hierarchical data model is a data model which the data is organized into a tree like structure.

• First commercial DBMS is based on this model.• In Hierarchical model data is represented as records

and the records organized as collection of trees.• The relationships among the data are represented by

links, which can be viewed as pointers.

Topic


5

Hierarchical Model


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Network Model• In Network model data is represented as records and

the records organized as collection of arbitrary graphs.• The relationships among the data are represented by

links, which can be viewed as pointers.• In network model a record can have any number of

parent records.

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5

Network Model


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• Database Schema refers to the overall structure of a database.• The description of a database is called the database schema,

which is specified during database design and is not expected to change frequently

Schema Diagram:

Student

Course

Teacher

Sub topic 5

Schemas, Instances, and Database State


Schema

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• The data in the database at a particular moment in time is called instance or database state.

• The distinction between database schema and database state is very important.

Database state:• At any point in time, the database has a current state.

subTopic

instance

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Instance:


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Topic

Three-Schema architecture

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Levels of Abstraction or Three-Schema architecture:


3-Schema Architecture

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• The internal schema uses a physical data model and describes the complete details of data storage and access paths for the database.

• It tells us what data is stored in the database and how. At least the following aspects are considered at this level:

• Storage allocation: B-trees, hashing etc.• Access paths: specification of primary and secondary

keys, indexes and pointers and sequencing..

Topic


6

Internal level or internal schema:


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• The conceptual level has a conceptual schema, which describes the structure of the whole database for a community of users.

• The conceptual schema hides the details of physical storage structures and concentrates on describing entities, data types, relationships, user operations, and constraints.

• Usually, a representational data model is used to describe the conceptual schema when a database system is implemented.

Topic


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Conceptual level or conceptual schema


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External level or External View:• The external or view level includes a number of external

schemas or user views.• The external level is the view that the individual user of

the database has.• Each external schema describes the part of the database

that a particular user group is interested in and hides the rest of the database from that user group.

Topic


6

External level or External View:


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• Data independence can be defined as the capacity to change the schema at one level of a database system without having to change the schema at the next higher level.

• We can define two types of data independence:

1 Physical data independence

2. Logical data independence

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Data Independence


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• Physical data independence is the capacity to change the internal schema without having to change the conceptual schema.

• Hence, the external schemas need not be changed as well.

• Changes to the internal schema may be needed because some physical files had to be reorganized-for example, by creating additional access structures-to improve the performance of retrieval or update.

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Physical data independence:


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• Logical data independence is the capacity to change the conceptual schema without having to change external schema or application programs.

• We may change the conceptual schema to expand the database (by adding a record type or data item), to change constraints, or to reduce the database (by removing a record type or data item).

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6

Logical data independence:


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The Functional components of a database system can be divided in to • Query Processor Components • Storage Manager Components

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DBMS architecture

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DBMS architecture


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DBMS architecture

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Architecture Diagram


Dbms Architecture

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The Query Processor Components include:DDL interpreter:• It interprets DDL statements and converts them in to a

set tables which are saved in the data dictionaryDML compiler:• It translates DML statements into low-level

instructions that are understood by the Query Evaluation Engine.

• It also optimizes the DML Queries for efficient execution by the Query Evaluation Engine.

Query evaluation engine:• It executes low-level instructions generated by the

DML compiler and produces results.

Topic

DBMS architecture

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Query Processor Components


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• These components provide the interface between the low-level data stored in the database and the Query Processor.

• The storage manager components include:Authorization and integrity manager: • It tests for the satisfaction of integrity constraints and

checks the authority of users to access data.Transaction manager: • This component ensures that concurrent transactions

proceed without conflict and the database remains in a consistent (correct) state despite system failures.

Topic

DBMS architecture

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Storage Manager Components


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File manager:• It manages the allocation of disk-space for the

storage of DBMS files.Buffer manager:• It is responsible for fetching data from disk

storage into main memory buffers for processing, and then writing the updated data back onto the disk.

Topic

DBMS architecture

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Storage Manager Components


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Data files:• Which store the database itself.Data dictionary:• It is a metadata file, which stores the database

schema. It stores metadata about the structure of the database.

Indices:• It can provide fast access to data items. Like the

index in this textbook, a database index provides pointers to those data items that hold a particular value.

Statistical data:• It stores the statistical information about processing

of previous queries. This information is used by the Query Processor to optimize the queries.

Topic

DBMS architecture

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Data Components


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Several criteria are normally used to classify DBMSs are1. Based on data model 2. No of users supported by the System3. Number of sites over which the database is distributed 4. Cost 5. Types of access path options 6. Based on purpose

Topic

CLASSIFICATION OF DATABASE MANAGEMENT

SYSTEMS

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CLASSIFICATION OF DATABASE MANAGEMENT SYSTEMS


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• The main data model used in many current commercial DBMSs is the relational data model.

• The object data model was implemented in some commercial systems but has not had widespread use.

• Many legacy (older) applications still run on database systems based on the hierarchical and network data models.

• We can hence categorize DBMSs based on the data model: relational, object, relational, hierarchical, network, and other.

Topic


SYSTEMS

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1.Based on Data Model:


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Multi-user vs. single-user • Single-user systems support only one user at a time

and are mostly used with Personal computers.• Multiuser systems, support multiple users concurrently.

Topic


SYSTEMS

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2.No of users supported by the System::


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Centralized vs. distributed•A DBMS is centralized if the data is stored at a single computer site. A centralized DBMS can support multiple users, but the DBMS and the database themselves reside totally at a single computer site. •A distributed DBMS (DDBMS) can have the actual database and DBMS software distributed over many sites, connected by a computer network.

Topic


SYSTEMS

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3. Number of sites over which the database is distributed


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•The majority of DBMS packages cost between $10,000 and $100,000.•Single-user low-end systems that work with micro computers cost between $100 and $3000. At the other end of the scale, a few elaborate packages cost more than $100,000.

Topic


SYSTEMS

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4. Cost


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• We can also classify a DBMS on the basis of the types of access path options for storing files. One well-known family of DBMSs is based on inverted file structures.Topic


SYSTEMS

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5. Access path


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• A DBMS can be general purpose or special purpose. When performance is a primary

• Consideration, a special-purpose DBMS can be designed and built for a specific application such a system cannot be used for other applications without major changes.

• Many airline reservations and telephone directory systems developed in the past are special purpose DBMSs.

Topic

CLASSIFICATION OF DATABASE

MANAGEMENT SYSTEMS

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6. General-purpose vs. special-purpose


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Topic

Phases of Database Design

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Requirements collection and analysis

Conceptual Design

Logical Design Data Model Mapping

Physical Design


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•In this step, the database designers interview prospective database users to understand and document their data requirements.• These requirements should be specified in as detailed and complete a form as possible

Topic


9

Requirements collection and analysis


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•Once all the requirements have been collected and analyzed, the next step is to create a conceptual schema for the database; using a high-level conceptual data model this step is called conceptual design. •The conceptual schema is a concise description of the data requirements of the users and includes detailed descriptions of the entity types, relationships, and constraints; these are expressed by using the ER Model•This approach enables the database designers to concentrate on specifying the properties of the data, without being concerned with storage details.

Topic


9

Conceptual Design


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• The next step in database design is the actual implementation of the database, using a commercial DBMS.

• Most current commercial DBMSs use an implementation data model such as the relational or the object-relational database model.

• In this phase the conceptual schema is transformed from the high-level data model into the implementation data model

Topic


9

Logical Design


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Physical Design•The last step is the physical design phase, during which the internal storage structures, indexes, access paths, and file organizations for the database files are specified.

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9

Characteristics


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• Entity-Relationship model is a popular high, level conceptual data model. This model and its variations are frequently used for the conceptual design of Database applications

• The ER model describes data as entities, relationships, and attributes.

• ER Model is best used for the conceptual design of database.

• ER Model is based on: Entities and their attributes, Relationships among entities

Topic

ER Model

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Entity-Relationship model


ER-Model

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• An entity, which is a "thing" in the real world with an independent existence.

• An entity may be an object with a physical existence (for example, a particular person, car, house, or employee) or it may be an object with a conceptual existence (for example, a company, a job, or a university course)

• In the University database context, an individual student, faculty member, a class room, a course are entities

Topic

ER Model

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Entity:


ER-Model

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• Attribute describes property or characteristics of an entity

• These are the properties of the entity. • For example, an employee entity may be described by

the employee's name, age, address, salary, and job. A particular entity will have a value for each of its attribute

Types of Attributes1. simple versus composite2. single-valued versus multivalued3. stored versus derived.

Topic

ER Model

Entity_20Relationship_20Model_module4_-1_PIP.mp4

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Attributes


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• Composite attributes can be divided into smaller subparts, which represent more basic attributes with independent meanings.

• For example, the Address attribute of the employee entity can be subdivided into StreetAddress, City, State, and Zip,3 with the values "2311 Kirby," "Houston," "Texas," and "77001."

• Attributes that are not divisible are called simple or atomic attributes.

• Ex: Zipcode

Topic

ER Model

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Composite versus Simple (Atomic) Attributes


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• Single-valued attribute is the attribute which is having only single value.

• Most attributes have a single value for a particular entity; such attributes are called single-valued.

• For example, Age, is a single-valued attribute of a person.

• Multi-valued attribute is the attribute which is having more than one value.

• an attribute can have a set of values for the same entity-for example, a Colors attribute for a car, or a phno attribute for a person.

Topic

ER Model

10

Single-Valued versus Multivalued Attributes


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•Derived attribute is one whose value can be calculated/derived from the values of other attributes. The Age and BirthDate attributes of a person.• For a particular person entity, the value of Age can be determined from the current (today's) date and the value of that person's BirthDate. •The Age attribute is hence called a derived attribute and is said to be derivable from the BirthDate attribute, which is called a stored attribute.

Topic

ER Model

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Stored versus Derived Attributes


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•An entity type defines a collection (or set) of entities that have the same attributes.•Each entity type in the database is described by its name and attributes.•A database usually contains groups of entities that are similar.•For example, a company employing hundreds of employees may want to store similar information concerning each of the employees. •These employee entities share the same attributes, but each entity has its own value(s) for each attribute.

Topic

ER Model

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Entity Types and Entity Sets


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•The collection of all entities of a particular entity type in the database at any point in time is called an entity set. •The entity set is usually referred to using the same name as the entity type.•An entity type is represented in ER diagrams as a rectangular box enclosing the entity type name. •An entity type describes the schema or intension for a set of entities that share the same structure

Topic

ER Model

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Entity Types and Entity Sets


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• An important constraint on the entities of an entity type is the key or uniqueness constraint on attributes.

• An entity type usually has an attribute whose values are distinct for each individual entity in the entity set. Such an attribute is called a key attribute, and its values can be used to identify each entity uniquely.

• For example, the Name attribute is a key of the COMPANY entity type because no two companies are allowed to have the same name.

• For the Employee entity type typical key attribute is Empid.

Topic

ER Model

Mod_207.1.mp4

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Key Attributes of an Entity Type


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Notations of ER Diagrams

Topic

ER Model

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Notations of ER Diagrams


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Example Database Application: COMPANY• Initial Conceptual Design of COMPANY database• Suppose that Requirements Collection and Analysis

results in the following (informal) description of the COMPANY mini world:

• The company is organized as a collection of departments.

• Each department • has a unique name • has a unique number • is associated with a set of locations • has a particular employee who acts as its manager

(and who assumed that position on some date) • has a set of employees assigned to it • controls a set of projects

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Example Database Application: COMPANY


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Each project • has a unique name • has a unique number • has a single location • has a set of employees who work on it • is controlled by a single department

Each dependent • has first name • has a sex • has a birthdate • is related to a particular employee in a

particular way (e.g., child, spouse, pet) • is uniquely identified by the combination of

her/his first name and the employee of which (s)he is a dependent

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Cont ...


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Each employee • has a name • has a SSN that uniquely identifies her/him • has an address • has a salary • has a sex • has a birthdate • has a direct supervisor • has a set of dependents • is assigned to one department • works some number of hours per week on

each of a set of projects (which need not all be controlled by the same department)

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Cont ...


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Cont...


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•It is Association among two or more entities. •When two or more entities are associated with each other, we have an instance of a Relationship.•A relationship relates two or more distinct entities with a specific meaning.•It is represented by a diamond. •Relationships can have their own attributes •Whenever an attribute of one entity type refers to an entity (of the same or different entity type), we say that a relationship exists between the two entity types

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Relationship:


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Relationship diagram:


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• Relationships of the same type are grouped or typed into a relationship type.

• For example, the WORKS_ON relationship type in which EMPLOYEEs and PROJECTs participate, or the MANAGES relationship type in which EMPLOYEEs and DEPARTMENTs participate.

.

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Relationship Type:


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Relationship set


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•The degree of a relationship is the number of participating entities. •It refers to number of entity sets that participate in a relationship set. •The degree of WORKS-FOR relationship is two.•A Relationship type of degree two is called binary, and a Relationship type of degree three is called ternary. •In ER diagrams, relationship types are displayed as diamond-shaped boxes, which are connected by straight lines to the rectangular boxes representing the participating entity types.

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Degree of a Relationship Type


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• A relationship type can have attributes describing properties of a relationship.

• FOR EXAMPLE Ramireddy works for CSE Department since 2011

• WOEKS-FOR relationship type have attributes like empid, deptid and since.

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Relationship Attributes


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• Relationship types usually have certain constraints that limit the possible combinations of entities that may participate in the corresponding relationship set.

• For example if the company has a rule that each employee must work for exactly one department, then we would like to describe this constraint in the schema.

• Two main types of relationship constraints1. Cardinality ratio 2. Participation.

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Constraints on Relationships


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• The cardinality ratio for a binary relationship specifies the maximum number of relationship instances that an entity can participate in.

• For example, in the WORKS_FOR binary relationship type, DEPARTMENT: EMPLOYEE is of cardinality ratio l: N, meaning that each department can be related to (that is, employs) any number of employees but an employee can be related to (work for) only one department.

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Cardinality Ratios for Binary Relationships


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For a binary relationship set the mapping cardinality must be one of the following types:• One to One(1:1)• One to many(l:N)• Many to one(N:l)• Many to many (M:N)

• Consider binary relationship set R between entity sets A and B

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Cardinality Ratios for Binary Relationships


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•An entity in A is associated with at most one entity in B, and an entity in B is associated with at most one entity in A.•An example of a 1:1 binary relationship is MANAGES which relates a department entity to the employee who manages that department. This represents the mini-world constraints that at any point in time-an employee can manage only one department and a department has only one manager.

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One to One (1:1)


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• One to Many: An entity in A is associated with many entities in B and an entity in B is associated with at most one entity in A.

• Many to One: An entity in A is associated with at most one entity in B, an entity in B is associated with many entities in A.

• Ex: an employee works in a single department but a department consists of many employees.

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Cardinality Ratios


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• Many to Many: An entity in A is associated with many entities in B, and an entity in B is associated with many entities in A.

• Ex: The relationship type WORKS_ON is of cardinality ratio M:N, because the mini-world rule is that an employee can work on several projects and a project can have several employees.

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Cardinality Ratios


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• This constraint specifies the minimum number of relationship instances that each entity can participate in, and is sometimes called the minimum cardinality constraint.

• There are two types of participation constraints1 total participation2. Partial participation

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Participation Constraints


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total participation:• If a company policy states that every

employee must work for a department, then an employee entity can exist only if it participates in at least one WORKS_FOR relationship instance Thus, the participation of EMPLOYEE in WORKS_FOR is called total participation, meaning that every entity in "the total set" of employee entities must be related to a department entity via WORKS_FOR. Total participation is also called existence dependency.

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Characteristics


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• We do not expect every employee to manage a department, so the participation of EMPLOYEE in the MANAGES relationship type is partial, meaning that some or "part of the set of" employee entities are related to some department entity via MANAGES, but not necessarily all.

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Partial participation:


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• Entity types that do not have key attributes of their own are called weak entity types.

• In contrast, regular entity types that do have a key attribute are also called strong entity types.

• Entities belonging to a weak entity type are identified by being related to specific entities from another entity type in combination with one of their attribute values

• Weak entity type always has a total participation constraint (existence dependency) with respect to its identifying relationship, because a weak entity cannot be identified without an owner entity.

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WEAK ENTITY TYPES


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ER DIAGRAM – Relationship Types are: WORKS_FOR, MANAGES, WORKS_ON, CONTROLS,SUPERVISION, DEPENDENTS_OFTopic

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Company ER Diagram


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• The ER model is generally sufficient for "traditional" database applications.

• But more recent applications of DB technology (e.g., CAD/CAM, telecommunication, images/graphics, multimedia, data mining/warehousing, geographic info systems) cry out for a richer model.

• The EER (Enhanced ER) model includes all the modeling concepts of the ER model ,In addition, it includes the concepts of subclass and superclass and the related concepts of specialization and generalization.

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EER Model

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EER (Enhanced Entity Relationship) Model


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• Another concept included in the EER model is that of a category or union type which is used to represent a collection of objects that is the union of objects of different entity types

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EER (Enhanced Entity Relationship) Model


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•An entity type is used to represent both a type of entity and the entity set or collection of entities of that type that exist in the database.

•For example, the entity type EMPLOYEE describes the type (that is, the attributes and relationships) of each employee entity, and also refers to the current set of EMPLOYEE entities in the COMPANY database.

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SUBCLASSES, SUPERCLASSES AND INHERITANCE


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•An entity type is used to represent both a type of entity and the entity set or collection of entities of that type that exist in the database.•For example, the entity type EMPLOYEE describes the type (that is, the attributes and relationships) of each employee entity, and also refers to the current set of EMPLOYEE entities in the COMPANY database.

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• The set of entities in each of the latter groupings is a subset of the entities that belong to the EMPLOYEE entity set, meaning that every entity that is a member of one of these sub groupings is also an employee.

• We call each of these sub groupings a subclass of the EMPLOYEE entity type, and the EMPLOYEE entity type is called the super class for each of these subclasses

• We call the relationship between a super class and anyone of its subclasses a super class/subclass or simply class/subclass relationship.

• In our previous example, EMPLOYEE/SECRETARY and EMPLOYEE/TECHNICIAN are two class/subclass relationships.

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• The set of entities in each of the latter groupings is a subset of the entities that belong to the EMPLOYEE entity set, meaning that every entity that is a member of one of these sub groupings is also an employee.

• We call each of these sub groupings a subclass of the EMPLOYEE entity type, and the EMPLOYEE entity type is called the super class for each of these subclasses

• We call the relationship between a super class and anyone of its subclasses a super class/subclass or simply class/subclass relationship.

• In our previous example, EMPLOYEE/SECRETARY and EMPLOYEE/TECHNICIAN are two class/subclass relationships.

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• Specialization is the process of defining a set of subclasses of an entity type;

• That entity type is called the super class of the specialization.

• The set of subclasses that form a specialization is defined on the basis of some distinguishing characteristic of the entities in the super class

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Specialization


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Specialization


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Specialization


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The specialization process allows us to do the following:

• Define a set of subclasses of an entity type• Establish additional specific attributes with

each subclass• Establish additional specific relationship

types between each subclass and other entity types or other subclasses

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specialization


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• The term generalization to refer to the process of defining a generalized entity type from the given entity types.

• Generalization a reverse process of abstraction in which we suppress the differences among several entity types, identify their common features, and generalize them into a single super class of which the original entity types are special subclasses.

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Generalization.mp4

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Generalization


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• Hence, in below Figure we can view {CAR, TRUCK} as a specialization of VEHICLE, rather than viewing VEHICLE as a generalization of CAR and TRUCK.

• Similarly, in previous figure we can view EMPLOYEE as a generalization of SECRETARY, TECHNICIAN, and ENGINEER.

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Generalization


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Generalization


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Generalization


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Assignment Questions:

• Discuss various disadvantages in the file system and explain how it can be overcome by the database system

• Explain the advantages of DBMS? What is DBA and describe the responsibilities of DBA?

• Consider your own assumptions and draw an ER model for “University Database”


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Assignment Questions:

• Construct an E – R diagram for the database of a hospital with a set of patients and a set of doctors. With each patient a log of the various test conducted is also associated. Construct the appropriate relations for this diagram.

• Consider your own assumptions and draw an ER model for “Sales Order Processing”.


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Gate Questions

Consider the following ER diagram.(GATE-2008)

The minimum number of tables needed to represent M, N, P, R1, R2 is(A) 2(B) 3(C) 4(D) 5


http://www.geeksforgeeks.org/wp-content/uploads/GATE2008DBMS_ERDIA.gif

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Gate Questions


Answer (A)Explanation:Many-to-one and one-to-many relationship sets that are total on the many-side can be represented by adding an extra attribute to the “many” side, containing the primary key of the “one” side. Since R1 is many to one and participation of M is total, M and R1 can be combined to form the table {M1, M2, M3, P1}. N is a week entity set, so it can be combined with P.

http://en.wikipedia.org/wiki/Weak_entity

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Gate Questions


Let E1 and E2 be two entities in an E/R diagram with simple single-valued attributes. R1 and R2 are two relationships between E1 and E2, where R1 is one-to-many and R2 is many-to-many. R1 and R2 do not have any attributes of their own. What is the minimum number of tables required to represent this situation in the relational model?(GATE-2005)(a) 2(b) 3(c) 4(d) 5Answer (c)

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Gate Questions


Given the basic ER and relational models, which of the following is INCORRECT?(GATE-2012)

(A) An attributes of an entity can have more than one value(B) An attribute of an entity can be composite(C) In a row of a relational table, an attribute can have more than one value(D) In a row of a relational table, an attribute can have exactly one value or a NULL value

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Gate Questions


Answer (C)Explanation: The term ‘entity’ belongs to ER model and the term ‘relational table’ belongs to relational model.A and B both are true. ER model supports both multi valued and composite attributes (C) is false and (D) is true. In Relation model, an entry in relational table can have exactly one value or a NULL.

Engineering

DBMS Bascis