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Data warehousing concepts
1. What is difference between view and materialized view?Views
contains query whenever execute views it has read from base
tableWhere as M views loading or replicated takes place only once
which gives you better queryperformance
Refresh m views 1.on commit and . on demand!"omplete# never#
fast# force$
2. What is bitmap index why its used for DW ?a bitmap for each
key value replaces a list of rowids. %itmap index more efficient
for datawarehousing because low cardinality# low updates# very
efficient for where class
!. What is star schema? "nd what is snowfla#e schema?&he
center of the star consists of a large fact table and the points of
the star are the dimensiontables.
'nowflake schemas normali(ed dimension tables to eliminate
redundancy. &hat is# the)imension data has been grouped into
multiple tables instead of one large table.
'tar schema contains demorali(ed dimension tables and fact
table# each primary key values indimension table associated with
foreign key of fact tables.*ere a fact table contains all business
measures !normally numeric data$ and foreign key values#and
dimension tables has details about the sub+ect area.
'nowflake schema basically a normali(ed dimension tables to
reduce redundancy in the dimensiontables
$.Why need staging area database for DW ?'taging area needs to
clean operational data before loading into data warehouse."leaning
in the sense your merging data which comes from different
source
%.What are the steps to create a database in manually?create os
service and create init file and start data base no mount stage
then give create data basecommand.
&.Difference between '()* and DW ?,-& system is
basically application orientation !eg# purchase order it is
functionality of anapplication$Where as in )W* concern is sub+ect
orient !sub+ect in the sense custorer# product# item# time$'()*/
0pplication ,riented/ sed to run business/ )etailed data/ "urrent
up to date/ 2solated )ata/ Repetitive access/ "lerical ser /
erformance 'ensitive/ 3ew Records accessed at a time !tens$/ Read4
pdate 0ccess/ 5o data redundancy/ )atabase 'i(e 166M%7166 8%DW/
'ub+ect ,riented/ sed to analy(e business/ 'ummari(ed and refined/
'napshot data/ 2ntegrated )ata/ 0d7hoc access
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/ 9nowledge ser / erformance relaxed/ -arge volumes accessed at
a time!millions$/ Mostly Read !%atch pdate$/ Redundancy present/
)atabase 'i(e 166 8% 7 few terabytes
+.Why need data warehouse?
0 single# complete and consistent store of data obtained from a
variety of different sources madeavailable to end users in a what
they can understand and use in a business context.
0 process of transforming data into information and making it
available to users in a timely enoughmanner to make a difference
2nformation
&echnique for assembling and managing data from various
sources for the purpose of answeringbusiness questions. &hus
making decisions that were not previous possible
,.What is difference between data mart and data warehouse?
0 data mart designed for a particular line of business# such as
sales# marketing# or finance.
Where as data warehouse is enterprise7wide4organi(ational
&he data flow of data warehouse depending on the
approach
-.What is the significance of surrogate #ey?'urrogate key used
in slowly changing dimension table to track old and new values and
it:s derivedfrom primary key.
1 .What is slowly changing dimension. What #ind of scd used in
your pro/ect?)imension attribute values may change constantly over
the time. !'ay for example customerdimension has customer;id#name#
and address$ customer address may change over time.*ow will you
handle this situation
