Database Management Systems- 11

8/8/2019 Database Management Systems- 11

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DATABASEDATABASEMANAGEMENTMANAGEMENTSYSTEMSSYSTEMS

DATABASEDATABASEMANAGEMENTMANAGEMENTSYSTEMSSYSTEMS


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Data & Information

Data- Historically the term Datareferred to known facts that could

be recorded & stored on computermedia but today it consists of facts,texts, graphics, images, sound &

video segments that have meaning inusers environment.

Information- processes data onwhich decisions & actions are based.


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Data & Information

For decision to be meaningful, processed data mustqualify for following characteristics: Timely Accurate Complete Given to right person.

Meta Data- Data about data. (Rules, structures,description of Data).

Data Dictionary/ System catalog- contains Meta data.

DATA PROCESSING INFORMATION

(Raw facts) (Useful

Interpretation)


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Concepts Database-Group of related files of

different record types (Relateddata)

DBMS- set of programs that enablesusers to create and maintaindatabase.

Database Systems- DB + DBMS


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DBMSCombination of Hardware & Softwarethat can be used to set up & monitor a

database, and can manage the updating& retrieval of database that has beenstored in it.


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Database Management System(DBMS)

A software package such as Oracle or MS-Access.Manages data and relationships in the database.Creates a Data Dictionary to store Metadata dataabout data.Manages all day-to-day transactions.Provides user with data independence at applicationlevel.Transforms logical data requests to match physicaldata structures.Secures access through passwords, restricted useraccess, and encryption.Provides backup and recovery mechanisms.Provides export and import utilities.Allows sharing of data with locking capabilities


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.

V1

.

U1

P2

P3

U4

.

DATABASE

DBMS

V2

V3

V4

USERS

or APPL

PROGRAMS

VIEWS

of the

Database

Simplified Picture of

Database System


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Capabilities/ Functionalities ofDBMS

Creating a file, addition to data, deletion ofdata, modification of data: Creation, Addition& Deletion of entire files.

Retrieving the data collectively & Selectively.

Data can be stored or indexed at usersdiscretion & direction. Various reports can be produced from

systems. Mathematical Functions can be performed &

data stored in database can be manipulatedwith these functions to perform desiredcalculations.

Maintaining data Integrity.


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DBMS interprets & processes usersrequests to retrieve information fromdatabase.

Allow users to access data anywhere in

the database without knowledge of howdata are actually organized on storagedevice.

queries

COBOL / PL

/ FORTRAN

DBMS OPERATINGSYSTEM DataBase


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Database Applications:

Banking: all transactionsAirlines: reservations, schedules

Universities: registration, gradesSales: customers, products, purchasesManufacturing: production, inventory,

orders, supply chainHuman resources: employee records,salaries, tax deductions


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Database

Collection of all required informationpertaining to particular subject.

Data in Database is stored in Tables.Each Table contains number ofRecords. Each record has Field thathas unique values. Each record in

Table is a unique set of relatedFields. To cope it all, database storedin a computer is a File.


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ANSI/SPARC

architectureAmerican National Standards Institute -

Standards Planning and Requirements

CommitteeDefine three layers

External: view of users or applicationsdata

Conceptual: Enterprise "CommunitySchema

Internal: Physical representation of data


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.

.

EXTERNAL

SCHEMA 1

EXTERNAL

SCHEMA n

CONCEPTUAL

SCHEMA

INTERNAL

SCHEMA

........

USER INTERFACE

INTERFACE:

External to

Conceptual Schema

INTERFACE:

Conceptual to

Internal Schema

Database

Internal to

Database

Interface

DBMS: Responsible

for all INTERFACES

The ANSI/SPARC

3-level DBMS Architecture


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External layer Different users can use and see

different data

Data can be represented in differentway or can contain derived orcalculated fields

Users can see only the own data


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Conceptual layer

Describes the logical structure of thedatabase

Each of the entities, attributes and

relationship Integrity constraints

Semantic information (meaning of thedata)

Each external view can be derived fromthe conceptual layer

Independent from the storage


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Internal layer Physical representation of the data

Indexes

Data compression

Data encryption

Usually independent from the DBMS


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Benefit of the ANSI/SPARC

architectureEach of users has own customized view andthese views are independent of each other

Logical IndependenceImmunity of the external schemas tochanges in the conceptual schema (withsome limitation)

Physical IndependenceImmunity of the conceptual schema tochanges in the internal schema


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Data Abstraction Physical level describes how a record (e.g.,

customer) is stored. Logical level: describes data stored in database,

and the relationships among the data.

type customer = recordname : string;street : string;city : integer;

end;

View level: application programs hide details ofdata types. Views can also hide information (e.g.,salary) for security purposes.


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Levels of Abstraction Many views, single

conceptual (logical)schema and physicalschema. Views describe how

users see the data.

Conceptual schemadefines logicalstructure

Physical schemadescribes the files andindexes used.

Schemas are defined using DDL; data is modified/queried using DML.

Physical Schema

Conceptual Schema

View 1 View 2 View 3


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Instances and Schemas Similar to types and variables in programming languages

Schema the logical structure of the database Example: The database consists of information about a set of

customers and accounts and the relationship between them)

Analogous to type information of a variable in a program

Physical schema: database design at the physical level

Logical schema: database design at the logical level Instance the actual content of the database at a particular

point in time Analogous to the value of a variable

Physical Data Independence the ability to modify the

physical schema without changing the logical schema Applications depend on the logical schema

In general, the interfaces between the various levels andcomponents should be well defined so that changes in some partsdo not seriously influence others.


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Database Management Systems- 11

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