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Module-II
Database and databasemanagement system
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Difference between files and Relationaldatabase
Files1. Store data in one
dimensional files
2. Stores, organize
and retrieveinformation fromone file at a time
3. Leave the
management ofdata relationshipsto the applicationsthat access the
data.
Relational database1. Store data in twodimensionaltables
2. Store organizesand retrieveinformation islinked by acommon columnor field
3. Establishrelationshipsbetween files andviews within the
database itself.
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4. Require aprogrammer towrite code for datamanagementfunctions.
5. Files are createdand maintained byapplicationprograms.
6. Are often
associated witholder programs onmainframe andmid-range system.
4.Are typically createdand maintained by
databaseadministrators.
5.Are popular on
UNIX processorsand powerful serverwithin aclient/server
framework6. Consists a database
engine thatperforms differentfunctions.
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Database
Database is an integrated and well defined
data and information,centrally controlled in allits aspects,created and stored in atypicalstructure for an organization.
In an organization the database could be one
or more depending upon the needs and theoperations of the organization.
The data structure and its storage should besuch that it facilitates
sharability,availability,and integrity of data.Database excludes transient data such asreports,input documents,intermediate resultsobtained during processing
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Objectives of Database
1. Controlled Redundancy
2. Ease of learning and use
3. Data independence4. More information at low cost
5. Accuracy and integrity
6. Recovery from failure7. Privacy and security
8. Performance
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Advantages of Database Approach
All the three levels of management use thesame database hence any report using the
information will be consistentAll the three levels of management view thedatabase as per their needs.
The application systems can be developedindependent of the database.The data validation and updating will be onceand same for all
The data is shared by all userData security and privacy can be managed
AS the database is a storage of structuredinformation the queries can be answered fast.
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User programs
Application program or queries
Software to process
Queries/Programs
S/W to access
Stored Data
Stores
database
definition
Stored data
base
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Major types of databases used byOrganization and users
Computer using organizations havefive types of databases.
1. Common operational database
2. Common end user database
3. Distributed database
4. Personal and end user databases and5. External database
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databases
These databases consists of avariety of data files developed byend users at their
workstations.Users may have theirown electronic copies ofdocuments they generated withword processing packages orreceived by e-mails, fromelectronic spreadsheets and DBMSpackages.
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Distributed databaseThese are databases of local work groupsand departments at regional office,branchoffices manufacturing plant and other worksites.These database can include segments
of both common operational and commonuser databases as well as data generatedand used only at a users own site.
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Common operational databaseThese databases store detaileddata needed to support theoperation of entire
organization.They also calledsubject areadatabases,transaction databases
and production databases.For example Customerdatabase,personnel
database,accounting database
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These databases store data and
information extracted from selectedoperational and external databases.theyconsists of summarized data andinformation most needed by theorganisation managers and other endusers.They are also called informationdatabases and management databases
and accessed by executive and users aspart of DSS And EIS to supportmanagerial decision making.
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External databases
These can be accessed from large,privatelyowned databases or databanks available fora fee to end users and organisations fromcommercial information service
networks.Data is available in the form ofstatistics on economic and demographicactivity from statistical data banks; abstracts
from hundreds of newspapers,magazines andother periodicals from bibliographic databanks.
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Data base management system
DBMS is a collection of programs that enables users to create and maintain
a database.The DBMS is a general purpose software system that facilitatesthe processes of defining,constructing and manipulating databases forvarious applications.
Defining database involves specifying the data type structures andconstraints for the data to be stored in the database.
Constructing the database is the processes of storing the database itselfon the storage medium that is controlled by DBMS.
Manipulating includes the updating of database or editing the databaseand generating reports from the data.
The DBMS is a S/W or a set of rules and methods that allows for
defining,creating,updating,reading ,maintenance and protection ofthe database.
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DBMS consists of a collection of inter-related
data and a set of programs to access thatdata.The collection data is usually referred toas database which contains information aboutone particular enterprise.
The primary goal of a DBMS is to provide anenvironment that is both convenient andefficient to use retrieving and storing database
information.DBMS is the interface between the user ofapplication programs on one hand and the
database on other.
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DBMS
DBMS as interface between applicationprogram and data base
User(or)
Application
program
DBMS Data base
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Major users of a DBMSpackage
Database integration and reporting
Application development
Database access and maintenance
Database creation and modification
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Components to a DBMS
These are:-
1. At least one person who owns' and isresponsible for the database.
2. A set of rules and relationships that defines
and governs the interactions amongelements of the database.
3. People who put data into the database
4. People who get data out of the database5. The database itself.
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Components of DBMS
DDL
DML
SQL
f
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Functions of DBMS
1. Organizes data:-Data are organised according to thespecifications of DDL.These are specified by the DBA at thetime of creation of database.
2. Integrates data:- Data are interrelated or linked together atthe elements level and can,therefore be assembled in manycombinations during execution of a particular applicationprogram.
3. Separates data:-A DBMS servers as a filter betweenapplication program and their associated data.It separatesthe logical description and relationship of data from the wayin which the data are physically stored.
4. Controls data: A DBMS appears to an applicationprogrammer to be an extension of the O.S S/W .As it receivesdata requests from host programs,it controls how and where
data are physically stored.5. Retrieves data:A record of data can be obtained via
DBMS1.Serially 2.Sequentially 3.Randomly by address4.Randomly by key 5. By structural link
6. Protects :A DBMS protects and secures both the content ofa database and relationships of data element . Data areprotected against by unauthorized users,physical damage,OS
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Data dictionary1. It is an encyclopedia of information concerning each
data element.It describes the data and its
characteristics,such as location,size,type of data,itidentifies the origin,the use,the ownership,and themethod of accessing and securing data.
2. The data dictionary can exist either on paper or as a
computer file.When it exist as a file,special S/W isnecessary to create and maintain it,and make itavailable for use such S/w is called a data dictionarysystem(DDS).DDSs can be acquired as separate S/W
packages or as DBMSs and computer aided S/Wengineering tools.
3. A good data dictionary would ensure consistentdefinitions of data across different databases,and if
there were a change to the data ,it would also
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Benefits of databasemanagement system
Reduced programming cost
Reduced Development and
implementation timeReduced program and file managementcosts.
Reduced data redundancy
Increased flexibility
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Language
Two languages are used to communicatewith data base are:
1. Data description Language(DDL)2. Data manipulation Language(DML)
r
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rLanguage(DDL)
It is used to create and describe the data anddefine the schema in a DBMS
It serves as an interface for applicationprograms that use the data.Once the data
dictionary has been created its definition must bentered into the DBMS.
For example,if a payroll program needs the
employment number of an employee the DDLdefines the employment number and the otherdata in the database and acts as an interfacebetween the payroll program and the files that
contain the employment number
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Structured Query Language
It is a non procedural language exclusivelydeals with data:
Data integrity
Data manipulationData access
Data retrieval
Data queryData security
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SQLIt allows the user to access the data from the
databases to specific queries,both onmainframes and on PCs.Here users cantransform their experience from one database
system to another without going into muchdetail.
There are four basic operation in SQL
1. Select2. Update
3. Insert
4. And delete
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Select statement enables users to query the database forspecific information
Update statement allow users to update the data.
Insert statement new data in the existing database.
Delete statement delete existing data from the database
Two types of question s can be asked by users in SQL:
-Static Question & dynamic Question
Static questions are routine and standardize and oncedefined,can be used repeatedly or generatingweekly,monthly and quarterly reports, S/W packagesgenerating static questions are sometimes referred to asreport writers.
Dynamic questions are ad hoc and specific to thedecision maker.
Characteristics of DBMS
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Characteristics of DBMSThe capability to store large amounts of datanecessary for users needs.They are stored ondirect accessible devices for on-line support.
The capacity to interrogating data files,retrievingand modifying data and recording the changes
The data are combined to form operational unitsto minimise the duplication of data and increaseaccess to all data in the database.
The control in the systems limits the access to thedatabase files and builds the confidentiality of alldata in these files.
Objectives of DBMS
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Objectives of DBMSProvide for mass storage of relevant data.
Make access to the data easy for the userProvide prompt response to user requests for data.
Make the latest modifications to the data baseavailable immediately
Eliminate redundant Data
Allow for multiple users to be active at one time
Allow for growth in the database system
Protect the data from physical harm andunauthorised access
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Major uses of DBMS
The four major uses of a DBMS packageare:
1. Database interrogation and reporting(forend users)
2. Application development(for end users andprogrammers)
3. Database access(for end users andinformation service staff)4. Database creation and modification(for end
users and database administrators)
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Data Independence
The ability to modify a schemadefinition in one level without affectinga schema definition in the next higherlevel is called data independence.
There are two levels of dataindependence
Physical data independenceLogical data Independence
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Physical data independence
It is the ability to modify the physicalschema without causing applicationprograms to be rewritten.Modifications
at the physical level occasionallynecessary in order to improveperformance.
L i l d t I d d
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Logical data Independence
It is the ability to modify the conceptual schemawithout causing application programs to berewritten.Modification at the conceptual level arenecessary whenever the logical structure of thedatabase is altered(addition of money-market
accounts in banking system).It is more difficult toachieve than physical data independence sinceapplication programs are heavily dependent onthe logical structure of the data they access.Theconcept of DI is similar in many respects to theconcept of abstract data types in modern PLs .Both hide implementation details from theusers.This allows users to concentrate on thegeneral structure rather than low level
implementations details.
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Data base BasicData items:-It is the smallest unit of data that
has meaning to its user .The data item issimply known as the field in dataprocessing.It may be treated as a moleculeof the database.For example a student name
in a database is called as a data item.Thedata item could occasionally be furtherbroken down is called atomic level forprocessing purposes.For example,a data item
such as a data would be a composite valuecomprising the date,day and year.Forexample your registration number etc.
In the organisation ,each department is
responsible to find out its own way of-
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Entities
All the real world object such as anemployee, a component in an inventory
or a space or it may be intangible suchas a even,a job description,identificationnumbers.All such items about whichrelevant information is stored in thedatabase are called Entities.
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Attributes
An attribute may be expressed as a numberor as a text.It may even be a scannedpicture,a sound sequence,a moving picturewhich is now possible in multimedia database
Data processing normally concern with acollection of similar entities and records
information about the same attributes of eachof them
Schema
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SchemaA schema is a logical database description andis drawn as a chart of the types of data that areused .It gives the names of the entities andattributes and specify the relationship betweenthem.It is a frame work into which the dataitem can be fitted.Like an information display
system such as that giving the arrival anddeparture time at airport and railwaystations,the schema will remain the samethough the value displayed in the system will
change from time to time.The relationshipbetween the entities occurring in the schemamay be one-to-one or one-to-many or many tomany or conditional.That means it is an overall
chart of all the data item type and record types
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Subschema
The term subschema refers to the sameview but for the data-item types and
record type which are used in aparticular user.Therefore many differentsub-schemas can be derived from oneschema
Analysis between schema and
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Analysis between schema andsub schema
If schema represent a road map ofDelhi showing the major historical sites
,educational institutions,railwaystations,roadway stations and airports,asubschema could be a similar mapshowing one route each from therailway station or the airport to IGNOUcampus at Maidan Garhi
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A general model of a database system
External schema
User view User viewUser view
Conceptual Schema
Internal Schema
Stored data
Three views of data
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Three views of dataDBMS is a collection of interrelated files and a set
of programs that allows several users to access
and modify these files.The concern for efficiently leads to the design of
complex data structure for the representationof data in the data base.As the database
system are often used by non computerprofessionals,this complexity must be hiddenfrom database system users. This is done bydefining levels of abstract as which thedatabase may be viewed,there are threeviews.
1. Logical or External view2. Conceptual view
3. Internal or Physical view
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External view or logical view
It is the highest level of abstraction asseen by a user
This level of abstraction describes onlythe part of entire database.
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Conceptual view
This is the next higher level of abstractionwhich is the sum total of users views.Thislevel describes what data are actually stored
in database.This level contains information about entiredatabase in terms of a small number ofrelatively simple structure.
It represents the entities and thererelationships.
It contains integrity rules and authorizationrules,but it does not contain informationabout how the data items are stored
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Internal View
This is the lowest level of abstraction atwhich one describes how the data are
physically stored And how we canaccess it.
It includes information on ordering of
records,block sizes,storage indexes,useof pointers,and access strategies beingused.
D t B Ad i i t t
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Data Base AdministratorA person who is having central control over
the data and the programs.Functions of DBA
1. Schema definition,2. Storage structure and access method
definition,3. Schema physical organisation for data
access,
4. Integrity constraint specification.5. Back up and restore database6. Monitor database performance and
efficiency.
File management vs database management
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File management vs. database management
Topic File Management Databasemanagement
Data redundancy May have highdegree of dataredundancy
Has a low degreeof dataredundancy
DataIndependence
Recognition ofrecord format or
access methodmeans theapplication has tobe changed
Similarrecognition has
little or no impacton application
ApplicationMaintenance Highermaintenance cost Low maintenancecost
Integrity controls Usually providedby programmer
Provided byDBMS
UnanticipatedQueries A customprogram has to A query languagecan be used
on
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on .Datarelationship
Handled byapplicationsif at all
An integralpart of DBMS
Overhead Little CPUand Storage
overhead
Moreprocessing
power andstorage isneeded
Databaseownership
Applicationsmay havetheir ownprivate data
All databelongs tothe DBMS
cont
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cont
DBA Not needed Needed tocoordinate and
resolve theneeds of theusercommunity
Availability oftrainedprogrammers
Mostprogrammersare trained touse filemanagement
The averageprogrammerneeds to betrained to usedatabasemanagement
Databasedesign
Data files maybe designed as
needed
More time andeffort is spent
to develop agood databasedesign
D t d l
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Data models
A data model is a collection of concepts that
can be used to describe the structure of adatabase.By structure of a database we meanthe data types,relationships and constraintsthat should hold on data.
Most of the data models also include a set ofbasic operations for specifying retrievals andupdates on the database.
A database model is the method of organizingdata and represents the logical relationshipamong data elements in database .
D t M d l
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Data Models
Data model is of three types1. Object based logical model:ER
model,Object oriented model,binary
model,Semantic data model,infological model,functional data model
2. Records based logicalmodels:Relational,Network,Hierarchical
3. Physical data model:Unifying
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Types of data model
Hierarchical Model
Net work ModelRelational model
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Types of Relationship
One-to-one:This relationship indicates aunique relation between two entities(student-regd-no,person and employment no.)
One-to-many:Here an entity can havemultiple relationships with other entities inthe database(Air bus and passengers,teacherand student)
Many-to-many:Here every entity can berelated to a number of entities.(teachers andstudents).
of database processing system in banking
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Bank database
DBMS
Operating System
Application Program
Banking Service data model
Installment loan
data modelChequing and
Savings data model
Chequing
Application
Installment loan
ApplicationSaving
Application
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It helps to establish explicit or logicalrelationships among various data elements of
multiple files and arrange the elements in ahierarchy.
Each box is a record,it is also termed asnode.
In this model each record in one level can berelated to multiple records on the next-lowerlevel.
A record that has a subsidiary records is
callec the parent and the subsidiary recordsare called children.
It follows 1:M relationship with other dataelements in the database
Schematic of a hierarchical tree structure
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Entity type
Record type
Entity type
The above figure provides the hierarchical model
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Here link fields establish the explicit relationships.
The links are represented by thin lines that
connect data elements of the various records inthe lower portion.
Once a sales person record is retrieved the link inthat record can lead to another record i,e
logically related to that salesperson.A link field inthe second record leads to a 3rd record,and so oncreating a chain through an entire set of file.
The system retrieve records from the hierarchy
through pointers,which are pieces of data thatidentifies the link between different records.Thedata nodes in this are linked to one anotherthrough a series of pointers,one of which isattached to the end of each record in the
database
Advantage Disadvantage
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Advantage DisadvantageWell suited for
modelinghierarchical data.
Top-down naturemakes
programmingefficient.
Based on one-way access fromsuperiors to subordinates.
Not suited for manyto-manyrelationships.
Difficult to inert subordinate recordswithout superior records.
Deleting superiors logically deletessubordinates.
Difficult to update record stored inmultiple locations.
Not suited for databases whererelationships change.
Network Model
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Network ModelIn this model,each record in a database canhave multiple parents.
It maintain Many-to-Many(M:M) relationship
In network model,databases can betranslated from hierarchical form to network
form and vice-versa.Data elements are linked through pointers.
In this model a child can have a number ofparents,where as in a hierarchical model a
child can have only one parent.Like hierarchical model the records are notlimited to only one superior.
A record may have many superior records
and many subordinate records.
Network Model
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Network Model
It allows entry into a database at multipoint
A group of interconnected nodes is called anetwork.
A subway map is an example of a
network.The subway stations are thenodes,and the tracks are the interconnectionsor network.
A common approach is multi
pointers,especially with a link node recordrepresenting the connection between twoentities.
Advantages Disadvantages
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Advantages DisadvantagesIt promotes flexibilityand data
accessibility,since dataelements at a lowerlevel can be accessedwithout accessing the
data elements abovethem.
It is efficient ,easy tounderstand,and can beapplied to many realworld problems thatrequire routinetransaction.
It is complex to designand develop
It requires that therelationships among alldata elements to bedefined before
development starts,andchanges often demanda major programmingefforts
For large database
,operation andmaintenance of thenetwork model aretime-consuming andexpensive
Relational Model
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Relational ModelIn relational model , data is represented
using two-dimensional tables,called relationof flat files
The flat files are made up of columns androws.
Each column represents a field,also referredto as an attribute.
Each row represent a record , also referred as
a tuple.It is well suited for business needs because oftheir flexibility
Relational Model
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Relational ModelRelational databases use three fundamentaloperations:
SELECT
PROJECT
JOIN
The select operation is used to selected therequested query.
The project operation creates a subset ofcolumns designed to meet the information
needs of the user.The JOIN operation joins or links two or moretables ,if the information requested by theuser is not found in one table
Example:MS Access,dbase IV,DB2
Advantages Disadvantages
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Advantages DisadvantagesQuery languages allow easeof use.
It can relate data in a tableas long as the two tablesshare at least one commonattribute.Thats why mostcommercial databases for
microcomputers use relationaldatabase
It enables a computer systemto accommodate a variety offile inquiries in an efficientmanner.
No need to know the innerstructure of the database
Data independence allow easy
structure modification
Query languagesconsume processing
time and memory
Data must be related toact upon
Set processing is not
suite3d to conventionalPLs.
Command affectsystem performance
Relational Database
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Relational Database
A DBMS can be regarded as relational only
if it obeys the following three rules.1. All information must be held in tables
2. Retrieval of this data must be possible
using the following types of operationSelect, Join,Project
3. A relationship between data must be
represented explicitly in that data itself.
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Aims of Relational Database
1. Performance
2. The ability to distribute data.
3. The ability to handle enormousquantity of data
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Distributed Processing
It refers to an architecture in which adatabase resides on a different machine tothe user process accessing it.
To put this in a different way,the front andback end processes are on differentmachines.Such a machine will obviouslynecessitate some form of communicationcapability between the machine and depends
entirely on a complex logical and physicalseparation between the front and back endprocesses and processing
Distributed database
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Distributed database
A distributed data system is a collection of sites
or connected by communication lineswhereby:
1. Each participating node houses a relational
database2. These databases are themselves fully
functional within their own location.
3. A logical global distributed database isdefined incorporating elements of each ofthe participating databases in order toevaluate a single occurrence of a database.
Normalisation
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NormalisationIt is the processes of simplifying the relationshipbetween data elements in a record.Throughnormalization, a collection of data in a recordstructure is replaced by successive recordstructures that are simpler and more predictableand therefore more manageable.The reasons whyit is carried out are:
1. To structure the data to maintain the data an itsrelationship.
2. To permit simple retrieval of data in response toquery and report requests.
3. To simplify the maintenance of the data throughupdated inventories and deletions.
4. To reduce the need to restructure or reorganizedata when application requirements arise.
Degree of Normalisation
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Degree of Normalisation1NF(First Normal Form)
2NF(Second Normal Form)3NF(Third Normal Form)
BCN(Boyce-codd Normal Form)
4NF(Fourth Normal Form)5NF(Fifth or Projection-Join NormalForm)
1NF(First Normal Form)
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1NF(First Normal Form)
This is the lowest level of normalization.Arelation is said to be in 1NF if there will
be no composite attributes,and everyattributes is single and describes oneproperty.
2NF(Second Normal Form)
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2NF(Second Normal Form)A relation is said to be in 2NF if it is in 1NFand non-key attributes are functionally
dependent on the key attribute(S).Further,ifthe key has more than one attribute then nonon key attributes should be functionallydependent upon a part of the key attributes.
An attribute is a non-key if it is not part ofthe primary key.
An attribute is functionally dependent on akey if the attribute contains only one value
which depends on that key .For eg:theattribute SALARY contains only one valuewhich depends on the key NAME.
3 ( hi d l )
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3NF(Third Normal Form)
Data is in 3NF if and only if it is in 2NF and every non-key
attribute is non-transitively dependent on the primary key.A3NF will be needed where all attributes in a relation tuple arenot functionally dependent ,then there will be unnecessaryduplication of data.The purpose of 3NF is to ensure that
attributes directly belong to the entity.Transitivity is a mathematical principle that states
If a relation is true between the first value and thesecond,and between the second and the third, then the
relationship must also be true between the first and the third.Examples If AC
If A=B and B=C,then A=C
Boyce-cod Normal form
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Boyce cod Normal form
When a relation has more than one possiblekey and the composite keys have a common
attribute and if an attribute of a compositekey is dependent on an attribute of the othercomposite key,a BCNF is need.For example
Professor(professor code,Dept,HOD,PercenttimeIt is assumed that
A professor can work in more than one
departmentThe percentage of time he spends in eachdepartment is given
Each department has only one HOD
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Fourth and Fifth Normal form
When attributes in a relation havemultivalued dependency, further
normalization to 4NF and 5NF arerequired