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Data Warehousing Basics Interview Questions and Answers (5)

What is meant by metadata in context of a Datawarehouse and how it is important?

Meta data is the data about data; Business Analyst or data modeler usually capture information about data - the source (where and how the data is originated), nature of data (char, varchar, nullable, existance, valid values etc) and behavior of data (how it is modified / derived and the life cycle ) in data dictionary a.k.a metadata. Metadata is also presented at the Datamart level, subsets, fact and dimensions, ODS etc. For a DW user, metadata provides vital information for analysis / DSS.

Differences between star and snowflake schemas?

Star schema
A single fact table with N number of Dimension

Snowflake schema
Any dimensions with extended dimensions are know as snowflake schema

Difference between Snow flake and Star Schema. What are situations where Snow flake Schema is better than Star Schema to use and when the opposite is true?

Star schema contains the dimesion tables mapped around one or more fact tables.
It is a denormalised model.
No need to use complicated joins.
Queries results fastly.
Snowflake schema
It is the normalised form of Star schema.
contains indepth joins ,bcas the tbales r splitted in to many pieces.We can easily do modification directly in the tables.
We hav to use comlicated joins ,since we hav more tables .
There will be some delay in processing the Query .

What is VLDB?

The perception of what constitutes a VLDB continues to grow. A one terabyte database would normally be considered to be a VLDB.

What's the data types present in bo?n what happens if we implement view in the designer n report

Three different data types: Dimensions,Measure and Detail.
View is nothing but an alias and it can be used to resolve the loops in the universe.

can a dimension table contains numeric values?

Yes.But those datatype will be char (only the values can numeric/char)

What is the difference between view and materialized view?

View - store the SQL statement in the database and let you use it as a table. Everytime you access the view, the SQL statement executes.

Materialized view - stores the results of the SQL in table form in the database. SQL statement only executes once and after that everytime you run the query, the stored result set is used. Pros include quick query results.

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