arc/attribute today for yesterday yesterday for today today or yesterday
customer-resp. agent YES YES YES
customer-city YES YES
sale district YES
Table 2. Temporal scenarios for the INVOICE fact
temporal hierarchies nontemporal hierarchies
flow measures SUM, AVG, MIN, MAX SUM, AVG, MIN, MAX
stock measures AVG, MIN, MAX SUM, AVG, MIN, MAX
unit measures AVG, MIN, MAX AVG, MIN, MAX
Table 3. Valid aggregation operators for the three types of measures (Lenz, 1997)
8 Rizzi
Copyright ?© 2007, Idea Group Inc. Copying or distributing in print or electronic forms without written permission of
Idea Group Inc. is prohibited.
Definition 15: A measure is said to be additive along a dimension if its
values can be aggregated along the corresponding hierarchy by the sum
operator, otherwise it is called nonadditive. A nonadditive measure is
nonaggregable if no other aggregation operator can be used on it.
Table 3 shows that, in general, flow measures are additive along all dimensions,
stock measures are nonadditive along temporal hierarchies, and unit measures are
nonadditive along all dimensions.
On the invoice scheme, most measures are additive. For instance, quantity has flow
type: the total quantity invoiced in a month is the sum of the quantities invoiced in
the single days of that month. Measure unit price has unit type and is nonadditive
along all dimensions.
Pages:
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73