DWH-INTRVIEW QTNS

8/17/2019 DWH-INTRVIEW QTNS

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1.WHAT IS DIMENSION TABLE?

A dimension table is w hich contains t extual description of data. (Or)

We can dene dimension table, which contains e ld level hierarchical ofinformation.And also every d imensional table has a primary ke y (PK) in it, whichrepresents t he complete table structure.

2.WHAT IS FACT TABLE?

A Fact table contains a ll the (FK) foreign keys o f dimension table andmeasures.Measures a re numeric c alculations, which are key performance indicators.

3.WHAT IS YOUR ROLE AS AN ETL DEVOLPER?

As a n ETL developer our role is t o load data into dimension tables a nd facttables.

4.WHAT ARE THE DIFFERENT MAPPINGS YOU DEVOLOPED IN

PROJECT?

Stage mappingsDimension mappingsFact mappings.

5.WHAT IS JUNK DIMENSION?

It stores all the ag values, Like ‘0’,’1’,”YES’,’NO’,’IN PROGRESS’,’COMPLETED’ in a separatedimension table, and it this dimension table is not related to any fact table

6.WHAT IS DEGENERATED DIMENSION?

It is a dimension, which is s tored In a Fact table, but it doesn’t have anyattributes i n dimensional table.

Ex: credit card number Transaction id


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7.WHAT IS CONFORMED DIMENSION?

A dimension, which is used in multiple locations is called conformeddimension. This d imension can be used across multiple fact tables i n singledatabase, or multiple data marts o r data warehouses.

8.WHAT ARE THE DIFFERENT TYPES OF FACTS?

Additive facts: These are the facts t hat can be summed up through all of thedimensions in the fact table.Ex:sales fact tables.

Semi-additive: These are the facts t hat can be summed p for some of thedimensions i n the fact table, but not the others.Ex:Daily b alance fact

Non-additive facts: These are the facts t hat cannot be summed up for any ofthe dimensions p resent in the fact table.

Ex: facts w hich have percentages , ratios ca lculated.

9.WHAT IS DATA MART?

A Subset of data warehouse i s know n a s da ta m art.

10.WHAT IS DATAWAREHOUSE? WHO IS THE FATHER OF DWH?

Data warehouse is a historical database, which is d esigned for decision-making purposes.

W.H Inmon and Ralph Kimball were known a s father of data warehouse.

11.WHAT ARE THE TYPES OF APPROACHES IN DATA MART?

Top down approach


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Extracts t he data from multiple sources a nd transforms t he data and loads i ntodata warehouse, then splits i nto individual data marts a nd gives a cess t o theusers t o respective data marts.

Bottom up approach

In we extract data from multiple sources a nd transform the data and loads i ntothe individual data marts, and then integrating into the data warehouse andgives t he access t o user to the data.

12.WHAT ARE THE TYPES OF DATA MARTS?

There are 2 types o f data marts.1.Dependant -a data m art that depends on w arehouse.2.Independant –a data mart that doesn’t depend on warehouse.

13.WHAT IS STAR SCHEMA?

A star schema is a centrally located fact table surrounded by d imensiontables.In star schema all dimensional tables w ill be in denormalized form.As t he t ables a re in d enormalized form Bitmap indexes a re supported.In the star schema every d imension table is d irectly linked fact table.

14.WHAT IS SNOW FLAKE SCHEMA?

When we split the denormalised dimensional tables in s tar schema, thosetends t o normalize dimension tables a ndIn snow ake schema B-TREE indexes ar e sup ported.In snow ake schema every d imensional table inter linked

15.WHICH SCHEMA PERFORMANCE WILL BE G OOD?

It depends; normally st ar schema performance will be good as d imensiontables i n star schema are directly c onnected to fact table, so the queryperformance will be good.


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16.IN WHICH TYPE OF SCHEMA YOUR PROJECT IS DESIGNED?

I have worked on n no of dimension tables b ut I noticed most of the

dimensions a re directly linked to fact table. But some of the dimension areinter linked to fact table so I can say it’s a combination of star and snowakeschema.

17.WHAT IS FACTLESS-FACT TABLE?

A fact less -fact table, which contains o nly ke ys and it doesn’t contain anymeasures ( or) facts.

18.WHAT IS CUMULATIVE FACT TABLES?

This t ype of fact table describes w hat has h appened over a period of time.Ex: This f act table may describe the total sales by p roduct by store by day.The facts for this type of fact tables are mostly additive facts

19.WHAT IS SNAPSHOT FACT TABLE?

This t ype of fact table describes t he states o f the things i n particular instanceof time. And usually includes more semi additive and non-additive facts.

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DWH-INTRVIEW QTNS