Dbms

Problems with file processing systems

Inconsistent data Inflexibility Limited data sharing Poor enforcement of standards Excessive program maintenance

Character :The most basic logical element is

character.Which consists of alphabetic, numeric or other symbol.

Field : It consists of grouping of characters.For example, the grouping of alphabetic characters.For example grouping of alphabetic characters in a person’s name form a name field.

Record :Related fields of data are grouped to form a record.File :A group of related records is a data file, or table.Database :The highest level in the hierarchy is the

database.A database is an integrated collection of logically related records or files.

Levels of Data

Controlled Redundancy Ease of learning and use Data independence Accuracy and Integrity Privacy and security Shared Recovery from failure Performance

Objectives of Data Base

Operational Data Base Analytical Data Base Data Warehouse Data Base Distributed Data Base End User Data Base External Data Base

Types of Data Bases

Data Bases store detailed data needed to support

operations of entire organization They are also called Subject Area Databases ,transaction

database and production database A customer database, inventory database, and other

database containing data generated by business operations

Operational Database

Databases store data extracted from selected operational

and external databases Consists of data mostly needed by an organization’s

managers and other end users They are also called management databases or information

databases They are the databases accessed by the online analytical

processing (OLAP) systems, decision support systems and executive information systems

Analytical Database

Stores data from current and previous years that has been

extracted from various operational and analytical databases of an organization

It is a central source of data that has been standardized and integrated so it can be used by managers and other end user professionals throughout an organization

Data Warehouse Databases

Databases of local work groups and departments at

regional offices, branch offices, manufacturing plants and other work sites

Can include segments of common operational and common user databases as well as data generated and used only at a user’s own site

Ensuring that all the data in distributed databases are consistently and concurrently updated

Distributed Database

These databases consist of a variety of data files

developed by end users at their workstations For example, users may have their own electronic copies

of documents they generated with word processing packages or received by electronic mail.

End User Database

Access to external online databases or data banks is

available for a fee from commercial information services , or for free of price from many sources on the internet

For example, data are available in the form of statistics on economic and demographic activity from statistical data banks

Abstracts from newspapers, magazines, and other periodicals from bibliographic data banks

External Database

DBMS is the software that permits an organization to

centralize data, manage them efficiently, and provide access to the stored data by application programs .

DBMS acts as an interface between the application program and the physical data files

DBMS has three components A data definition language A data manipulation language A data dictionary

Database Management System

The data definition language is the formal language used

by the programmers to specify the content and structure of database

It defines each data element as it appears in the database before that data element is translated into the forms required by application programs

Data Definition Language

This language contains commands that permits end users

and programmers to extract data from the database to satisfy information requests and develop applications

The most prominent data manipulation language today is structured query language (SQL)

Data Manipulation Language

This is an automated or manual file that stores definitions

of data elements and data characteristics such as usage, physical representation, ownership, authorization and security

Many data dictionaries can produce lists and reports of data utilization, groupings, program location and so on

Data Dictionary

Organizes data Integrates data Separates data Controls data Retrieves data Protects data

Functions of DBMS

Reduced programming costs Reduced development and implementation time Reduced program and file maintenance costs Reduced data Redundancy Increase flexibility

Benefits of DBMS

Data is not stored in a random fashion. It is organized for

efficient retrieval. Sequential organization Indexed Sequential Organization Inverted List Organization Direct Access Organization

Data Storage and Retrieval

It simply means storing and sorting in physical,

contiguous blocks within files on tape or disk Records are also in sequence within each block It is best suited in reading one record after another without

a search delay The records can be added only at the end of the file

Sequential Organization

Data is stored in physically contiguous blocks and uses

indexes to locate records Indexed Sequential Organization reduces the magnitude of

the sequential search and provides quick access for sequential and direct processing

The drawback is the extra storage space required for the index. It also takes long to search the index for data access or retrieval

Indexed Sequential Organization

It differ from the previous in the index level and record

storage The indexed sequential method has a multiple index for a

given key, whereas the inverted list method has a single index for each key type

In inverted list records are not needed to be stored in a particular sequence. They are placed in data storage area but indexes are updated for the record keys and location

Inverted lists are best for applications that request specific data on multiple keys

Inverted List Organization

In direct access file organization, records are placed

randomly throughout the file New records are added at the end of the file or inserted in

specific locations based on software commands Records are accessed by addresses that specify their disk

locations. An address is required for locating a record, for linking records , or for establishing relationships

Direct Access Organization

Hierarchical Data Model

Employee

Job assignments BenefitsCompensation

Performance Salary hist Pension Life insurance Health

Network Data Model

Course 2Course 1 Course 3

Student 1 Student 2 Student 3 Student 4 Student 5 Student 6

Relational Data Model

Dept .no

D name

D loc

Emp no

Dep. A

Dep. B

Dep. C

Emp. no

E name

E title

E sal

Dep. no

E1 D A

E2 D A

E3 D B

E4 D B

E5 D C

E6 D A

The schemes (schema) define categories of data and their

properties . External Schema or user schema is the user’s view of a

part of the database Conceptual Schema is the overall logical view of the

database Internal Schema or data storage definition is the way the

data is physically organized in storage

Data Schemes

External Schemas

General Model

User View

User View

User View

Conceptual Schema

InternalSchema

StoredDatabase

Each user of the database (an application program or a

person formulating a query ) is concerned with only a small portion of the database

Each user is interested in only a part of the entities in the database, only part of the attributes of those entities, and certain relationships among the entities

External schema consists basically of definitions of each of the various external record types in the external view

The external schema is written using the DDL portion of the user’s data sub language

External Schema

The conceptual schema is the logical view of the entire

database . It represents as closely as possible the real entities and their relationships .

It contains integrity rules and authorization rules, but it does not contain information about how the data items are stored

Conceptual Schema

The internal schema or physical data model describes how

the database is organized for physical storage and access

The internal schema includes information on ordering of records, block sizes, storage indexes, use of pointers and access strategies being used

Internal Schema

A mapping is a transaction of one schema to another In order for a user to access data, the user view of the data

as reflected in the external schema must be translated into the overall conceptual schema

In the same way, the conceptual/internal mapping translates logical descriptions of data in the conceptual schema to physical locations and access paths in the internal scheme

Mapping

Mapping between Schemas

External view External view External view

External schema1 External schema 2 External schema 3

Overall conceptualview

Conceptual schema

Internal schema(DDL)

Stored Database