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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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