<s>
In	O
computing	O
,	O
the	O
star	B-Application
schema	I-Application
is	O
the	O
simplest	O
style	O
of	O
data	B-General_Concept
mart	I-General_Concept
schema	B-Application
and	O
is	O
the	O
approach	O
most	O
widely	O
used	O
to	O
develop	O
data	O
warehouses	O
and	O
dimensional	O
data	B-General_Concept
marts	I-General_Concept
.	O
</s>
<s>
The	O
star	B-Application
schema	I-Application
consists	O
of	O
one	O
or	O
more	O
fact	O
tables	O
referencing	O
any	O
number	O
of	O
dimension	O
tables	O
.	O
</s>
<s>
The	O
star	B-Application
schema	I-Application
is	O
an	O
important	O
special	O
case	O
of	O
the	O
snowflake	B-Language
schema	I-Language
,	O
and	O
is	O
more	O
effective	O
for	O
handling	O
simpler	O
queries	O
.	O
</s>
<s>
The	O
star	B-Application
schema	I-Application
gets	O
its	O
name	O
from	O
the	O
physical	B-Application
model	I-Application
's	I-Application
resemblance	O
to	O
a	O
star	O
shape	O
with	O
a	O
fact	O
table	O
at	O
its	O
center	O
and	O
the	O
dimension	O
tables	O
surrounding	O
it	O
representing	O
the	O
star	O
's	O
points	O
.	O
</s>
<s>
The	O
star	B-Application
schema	I-Application
separates	O
business	O
process	O
data	O
into	O
facts	O
,	O
which	O
hold	O
the	O
measurable	O
,	O
quantitative	O
data	O
about	O
a	O
business	O
,	O
and	O
dimensions	O
which	O
are	O
descriptive	O
attributes	O
related	O
to	O
fact	O
data	O
.	O
</s>
<s>
A	O
star	B-Application
schema	I-Application
that	O
has	O
many	O
dimensions	O
is	O
sometimes	O
called	O
a	O
centipede	O
schema	B-Application
.	O
</s>
<s>
Having	O
dimensions	O
of	O
only	O
a	O
few	O
attributes	O
,	O
while	O
simpler	O
to	O
maintain	O
,	O
results	O
in	O
queries	O
with	O
many	O
table	O
joins	O
and	O
makes	O
the	O
star	B-Application
schema	I-Application
less	O
easy	O
to	O
use	O
.	O
</s>
<s>
Fact	O
tables	O
are	O
generally	O
assigned	O
a	O
surrogate	B-Application
key	I-Application
to	O
ensure	O
each	O
row	O
can	O
be	O
uniquely	O
identified	O
.	O
</s>
<s>
Dimension	O
tables	O
are	O
generally	O
assigned	O
a	O
surrogate	B-Application
primary	I-Application
key	I-Application
,	O
usually	O
a	O
single-column	O
integer	O
data	O
type	O
,	O
mapped	O
to	O
the	O
combination	O
of	O
dimension	O
attributes	O
that	O
form	O
the	O
natural	O
key	O
.	O
</s>
<s>
Star	B-Application
schemas	I-Application
are	O
denormalized	B-Application
,	O
meaning	O
the	O
typical	O
rules	O
of	O
normalization	B-Application
applied	O
to	O
transactional	O
relational	O
databases	O
are	O
relaxed	O
during	O
star-schema	O
design	O
and	O
implementation	O
.	O
</s>
<s>
The	O
benefits	O
of	O
star-schema	O
denormalization	O
are	O
:	O
</s>
<s>
Simpler	O
queries	O
–	O
star-schema	O
join-logic	O
is	O
generally	O
simpler	O
than	O
the	O
join	O
logic	O
required	O
to	O
retrieve	O
data	O
from	O
a	O
highly	O
normalized	B-Application
transactional	O
schema	B-Application
.	O
</s>
<s>
Simplified	O
business	O
reporting	O
logic	O
–	O
when	O
compared	O
to	O
highly	O
normalized	B-Application
schemas	O
,	O
the	O
star	B-Application
schema	I-Application
simplifies	O
common	O
business	O
reporting	O
logic	O
,	O
such	O
as	O
period-over-period	O
and	O
as-of	O
reporting	O
.	O
</s>
<s>
Query	O
performance	O
gains	O
–	O
star	B-Application
schemas	I-Application
can	O
provide	O
performance	O
enhancements	O
for	O
read-only	O
reporting	O
applications	O
when	O
compared	O
to	O
highly	O
normalized	B-Application
schemas	O
.	O
</s>
<s>
Fast	O
aggregations	O
–	O
the	O
simpler	O
queries	O
against	O
a	O
star	B-Application
schema	I-Application
can	O
result	O
in	O
improved	O
performance	O
for	O
aggregation	O
operations	O
.	O
</s>
<s>
Feeding	O
cubes	O
–	O
star	B-Application
schemas	I-Application
are	O
used	O
by	O
all	O
OLAP	B-Application
systems	O
to	O
build	O
proprietary	O
OLAP	B-Application
cubes	O
efficiently	O
;	O
in	O
fact	O
,	O
most	O
major	O
OLAP	B-Application
systems	O
provide	O
a	O
ROLAP	O
mode	O
of	O
operation	O
which	O
can	O
use	O
a	O
star	B-Application
schema	I-Application
directly	O
as	O
a	O
source	O
without	O
building	O
a	O
proprietary	O
cube	O
structure	O
.	O
</s>
<s>
The	O
image	O
of	O
the	O
schema	B-Application
to	O
the	O
right	O
is	O
a	O
star	B-Application
schema	I-Application
version	O
of	O
the	O
sample	O
schema	B-Application
provided	O
in	O
the	O
snowflake	B-Language
schema	I-Language
article	O
.	O
</s>
<s>
Each	O
dimension	O
table	O
has	O
a	O
primary	O
key	O
on	O
its	O
Id	O
column	O
,	O
relating	O
to	O
one	O
of	O
the	O
columns	O
(	O
viewed	O
as	O
rows	O
in	O
the	O
example	O
schema	B-Application
)	O
of	O
the	O
Fact_Sales	O
table	O
's	O
three-column	O
(	O
compound	O
)	O
primary	O
key	O
(	O
Date_Id	O
,	O
Store_Id	O
,	O
Product_Id	O
)	O
.	O
</s>
