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21. What is meant bt ETL?
    The overall data acquisition process, called ETL (extraction, transformation,and loading), is generally grouped into three main components :
  • Extraction : Involves obtaining the required data from the various sources.
  • Transformation : Source data undergoes a number of operations that prepare it for import into the data warehouse (target database). To perform this task, integration and transformation programs are used which can reformat, recalculate, modify structure and data elements, and add lime elements. They can also perform calculations, summarization, de-normal-ization, etc.
  • Loading : Involves physically placing extracted and transformed data in the target database. The initial loading involves a massive data import into the data warehouse. Subsequently, an extraction procedure periodically loads fresh data based on business rules and a pre–determined frequency.
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22. What are the types of dimensional schema?
    There are two types of dimensional schema :
  • Star schema
  • Snowflake schema
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23. What is star schema?
  Star schema, there is only one central fact table, and a set of dimension tables, one for each dimension. In star schema, each dimension is represented by only one table, and each table contains a set of attributes.
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24. What is snowflake schema?
  A snowflake schema avoids the redundancy of star schemas by normalizing the dimension tables. Therefore, a dimension is represented by several tables related by referential integrity constraints.
  Posted by Prafulla Kumar Anayak. (Dec 12, 2013)

Snowflake schema means a central located fact table is surrounded by denormalized dimension tables again these denormalized dimension table is splited one or more normalized dimension tables.

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25. What is meant by starflake schema?
  A starflake schema is a combination of the star and the snowflake schemas where some dimensions are normalized while others are not.
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