Databases Reference
In-Depth Information
Table 4.2
2-D View of Sales Data for
AllElectronics
According to
time
and
item
location
D
“Vancouver”
item
(type)
home
time
(quarter) entertainment computer phone security
Q1
605
825
14
400
Q2
680
952
31
512
Q3
812
1023
30
501
Q4
927
1038
38
580
Note:
The sales are from branches located in the city of Vancouver. The measure displayed is
dollars sold
(in thousands).
Table 4.3
3-D View of Sales Data for
AllElectronics
According to
time
,
item
, and
location
location
D
“Chicago”
location
D
“New York”
location
D
“Toronto”
location
D
“Vancouver”
item item item item
home home home home
time
ent. comp.phonesec. ent. comp.phonesec. ent. comp.phonesec. ent. comp.phonesec.
Q1
854
882
89
623
1087
968
38
872
818
746
43
591
605
825
14
400
Q2
943
890
64
698
1130
1024
41
925
894
769
52
682
680
952
31
512
Q3
1032
924
59
789
1034
1048
45
1002
940
795
58
728
812
1023
30
501
Q4
1129
992
63
870
1142
1091
54
984
978
864
59
784
927
1038
38
580
Note:
The measure displayed is
dollars sold
(in thousands).
in this way, we may display any
n
-dimensional data as a series of
-dimensional
“cubes.” The data cube is a metaphor for multidimensional data storage. The actual
physical storage of such data may differ from its logical representation. The important
thing to remember is that data cubes are
n
-dimensional and do not confine data to 3-D.
Tables 4.2 and 4.3 show the data at different degrees of summarization. In the data
warehousing research literature, a data cube like those shown in Figures 4.3 and 4.4 is
often referred to as a
cuboid
. Given a set of dimensions, we can generate a cuboid for
each of the possible subsets of the given dimensions. The result would form a
lattice
of
cuboids, each showing the data at a different level of summarization, or
group-by
. The
lattice of cuboids is then referred to as a data cube. Figure 4.5 shows a lattice of cuboids
forming a data cube for the dimensions
time
,
item
,
location
, and
supplier
.
The cuboid that holds the lowest level of summarization is called the
base cuboid
.
For example, the 4-D cuboid in Figure 4.4 is the base cuboid for the given
time
,
item
,
location
, and
supplier
dimensions. Figure 4.3 is a 3-D (nonbase) cuboid for
time
,
item
,
.
n
1
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