Star Schema : Star Schema is a relational database schema
for representing multimensional data. It is the simplest
form of data warehouse schema that contains one or more
dimensions and fact tables. It is called a star schema
because the entity-relationship diagram between dimensions
and fact tables resembles a star where one fact table is
connected to multiple dimensions. The center of the star
schema consists of a large fact table and it points towards
the dimension tables. The advantage of star schema are
slicing down, performance increase and easy understanding of
data.

Snowflake Schema : A snowflake schema is a term that
describes a star schema structure normalized through the use
of outrigger tables. i.e dimension table hierachies are
broken into simpler tables.

In a star schema every dimension will have a primary key.
# In a star schema, a dimension table will not have any
parent table.
# Whereas in a snow flake schema, a dimension table will
have one or more parent tables.
# Hierarchies for the dimensions are stored in the
dimensional table itself in star schema.
# Whereas hierachies are broken into separate tables in snow
flake schema. These hierachies helps to drill down the data
from topmost hierachies to the lowermost hierarchies.