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What is a star schema? Why does one design this way?
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Answer Posted / tanmay kumar meher
The star schema (sometimes referenced as star join schema)
is the simplest data warehouse schema, consisting of a
single "fact table" with a compound primary key, with one
segment for each "dimension" and with additional columns of
additive, numeric facts.
The star schema makes multi-dimensional database (MDDB)
functionality possible using a traditional relational
database. Because relational databases are the most common
data management system in organizations today, implementing
multi-dimensional views of data using a relational database
is very appealing. Even if you are using a specific MDDB
solution, its sources likely are relational databases.
Another reason for using star schema is its ease of
understanding. Fact tables in star schema are mostly in
third normal form (3NF), but dimensional tables are in de-
normalized second normal form (2NF). If you want to
normalize dimensional tables, they look like snowflakes
(see snowflake schema) and the same problems of relational
databases arise - you need complex queries and business
users cannot easily understand the meaning of data.
Although query performance may be improved by advanced DBMS
technology and hardware, highly normalized tables make
reporting difficult and applications complex.
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