Database Reference
In-Depth Information
a
b
Product
Key
Product
Name
...
Discontinued
...
Yes No
p1
prod1
...
No
...
0
1
p2
prod2
...
Yes
...
1
0
p3
prod3
...
No
...
0
1
p4
prod4
...
Yes
...
1
0
p5
prod5
...
No
...
0
1
p6
prod6
...
Yes
...
1
0
c
Customer
Key
Customer
Name
Postal
Code
Address
...
c1
cust1
35 Main St.
7373
...
c2
cust2
Av. Roosevelt 50 1050
...
c3
cust3
Av. Louise 233
1080
...
c4
cust4
Rue Gabrielle
1180
...
d
e
f
g
Product
Key
Customer
Key
Time
Key
Sales
Amount
c1 c2 c3 c4
p1 p2 p3 p4 p5 p6
Yes No
p1
c1
t1
100
1
0
0
0
1
0
0
0
0
0
0
1
p1
c2
t1
100
0
1
0
0
1
0
0
0
0
0
0
1
p2
c2
t2
100
0
1
0
0
0
1
0
0
0
0
1
0
p2
c2
t3
100
0
1
0
0
0
1
0
0
0
0
1
0
p3
c3
t3
100
0
0
1
0
0
0
1
0
0
0
0
1
p4
c3
t4
100
0
0
1
0
0
0
0
1
0
0
1
0
p5
c4
t5
100
0
0
0
1
0
0
0
0
1
0
0
1
Fig. 7.13 An example of evaluation of star queries with bitmap indexes. ( a ) Product
table. ( b )Bitmapfor Discontinued .( c ) Customer table. ( d ) Sales fact table. ( e )Bitmap
for CustomerKey .( f )Bitmapfor ProductKey .( g )Bitmapjoinindexfor Discontinued
We will study now how this query is evaluated by an engine using the indexing
strategies studied above.
An ecient evaluation of our example query would require the definition of
aB + -tree over the dimension keys CustomerKey and ProductKey and bitmap
indexes on Discontinued in the Product dimension table and on the foreign
key columns in the fact table Sales . Figure 7.13 a,c,d shows the Product and
Customer dimension tables and the Sales fact table, while the bitmap indexes
are depicted in Fig. 7.13 b,e,f.
Let us describe how this query is evaluated by an OLAP engine. The
first step consists in obtaining the record numbers of the records that satisfy
the condition over the dimension, that is, Discontinued = ' Yes '.Asshownin
the bitmap index (Fig. 7.13 b), such records are the ones with ProductKey
 
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