Problems with file processing systemsInconsistent dataInflexibilityLimited data sharingPoor enforcement of standardsExcessive program maintenance

Levels of DataCharacter :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.

Objectives of Data BaseControlled RedundancyEase of learning and useData independenceAccuracy and IntegrityPrivacy and securitySharedRecovery from failurePerformance

Types of Data BasesOperational Data Base Analytical Data BaseData Warehouse Data BaseDistributed Data BaseEnd User Data BaseExternal Data Base

Operational DatabaseData Bases store detailed data needed to support operations of

entire organizationThey are also called Subject Area Databases ,transaction

database and production databaseA customer database, inventory database, and other database

containing data generated by business operations

Analytical DatabaseDatabases store data extracted from selected operational and

external databasesConsists of data mostly needed by an organization’s managers

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

databasesThey are the databases accessed by the online analytical

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

Data Warehouse DatabasesStores 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

Distributed DatabaseDatabases 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

End User DatabaseThese 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.

External DatabaseAccess 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

Database Management System

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

Data Definition Language 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 Manipulation LanguageThis 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 DictionaryThis 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

Functions of DBMSOrganizes dataIntegrates dataSeparates dataControls dataRetrieves dataProtects data

Benefits of DBMSReduced programming costsReduced development and implementation timeReduced program and file maintenance costsReduced data RedundancyIncrease flexibility

Data Storage and Retrieval

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

Sequential organizationIndexed Sequential OrganizationInverted List OrganizationDirect Access Organization

Sequential OrganizationIt simply means storing and sorting in physical, contiguous

blocks within files on tape or diskRecords are also in sequence within each blockIt is best suited in reading one record after another without a

search delayThe records can be added only at the end of the file

Indexed Sequential OrganizationData 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

Inverted List OrganizationIt differ from the previous in the index level and record storageThe 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

Direct Access OrganizationIn 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 commandsRecords are accessed by addresses that specify their disk

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

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

Data Schemes 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 databaseConceptual Schema is the overall logical view of the databaseInternal Schema or data storage definition is the way the data

is physically organized in storage

General Model

External Schemas

User View

User View

User View

Conceptual Schema

InternalSchema

StoredDatabase

External SchemaEach 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

Conceptual SchemaThe 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

Internal SchemaThe 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

MappingA mapping is a transaction of one schema to anotherIn 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 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