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ETL Interview questions and Answers

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1. What is Data warehouse?
    In 1980, Bill Inmon known as father of data warehousing. "A Data warehouse is a subject oriented, integrated ,time variant, non volatile collection of data in support of management's decision making process".
  • Subject oriented : means that the data addresses a specific subject such as sales, inventory etc.
  • Integrated : means that the data is obtained from a variety of sources.
  • Time variant : implies that the data is stored in such a way that when some data is changed.
  • Non volatile : implies that data is never removed. i.e., historical data is also kept.
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2. What is the difference between database and data warehouse?
  A database is a collection of related data.
A data warehouse is also a collection of information as well as a supporting system.
  Posted by Manoj. (Jan 20, 2014)

A database is a collection of related data. Where as Data Warehouse stores historical data, the business users take their decisions based on historical data only.

  Posted by Harikumar. (Dec 31, 2013)

In Data base we can maintain only current data which was not more than 3 years But in datawarehouse we can maintain history data it means from the starting day of enterprise DDL commands it means ( Insert ,update,delete)we can do in Database In datawarehouse once data loaded in Datawarehouse we can do any DDL operatations.

  Posted by Hasini. (Dec 13, 2013)

Database is used for insert, update and delete operation where as datawarehouse is used for select to analyse the data.

  Posted by Abdul Baba Roshan. (Nov 24, 2013)
DatabaseData Warehouse
The tables and joins in DB are are complex since they are normalizedTables and joins are simple since they are de-normalized
ER Modeling techniques are used for database designDimension modeling techniques are used for database design
Optimized for write operation Optimized for read operrations
Performance is slow for analysis queriesHigh performance for anlytical queries
  Posted by Jyoti. (Oct 25, 2013)

Database uses OLTP concept Data warehouse uses OLAP concept, means Data warehouse stores historical data.

  Posted by Jagadeesh. (May 16, 2013)

A database is a collection related data and also it is related to same data. Where as come to Data warehouse, It is collection of data integrated from different sources and stored in one container for taking or ( getting knowledge) managerial decisions.

  Posted by Santhu. (May 12, 2013)

In database we are using CRUD operations means “create, read, use, delete” but in datawarehouse we are using select operation.

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3. What are the benefits of data warehousing?
  • Historical information for comparative and competitive analysis.
  • Enhanced data quality and completeness.
  • Supplementing disaster recovery plans with another data back up source.
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4. What are the types of data warehouse?
    There are mainly three type of Data Warehouse are :
  • Enterprise Data Warehouse
  • Operational data store
  • Data Mart
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5. What is the difference between data mining and data warehousing?
  Data mining, the operational data is analyzed using statistical techniques and clustering techniques to find the hidden patterns and trends. So, the data mines do some kind of summarization of the data and can be used by data warehouses for faster analytical processing for business intelligence.
Data warehouse may make use of a data mine for analytical processing of the data in a faster way.
  Posted by Santhu. (May 12, 2013)

Data mining is one of the key concept to analyze data in Datawarehouse.

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