Unrolling the agent hierarchy
Conceptual Modeling Solutions for the Data Warehouse
Copyright ?© 2007, Idea Group Inc. Copying or distributing in print or electronic forms without written permission
of Idea Group Inc. is prohibited.
implementation on the star schema is simplest. If some attributes or arcs require
different scenarios, the designer should specify them on a table like Table 2.
Additivity
Aggregation requires defining a proper operator to compose the measure values
characterizing primary events into measure values characterizing each secondary
event. From this point of view, we may distinguish three types of measures (Lenz
& Shoshani, 1997):
???. Flow.measures:.They refer to a time period, and are cumulatively evaluated
at the end of that period. Examples are the number of products sold in a day,
the monthly revenue, the number of those born in a year.
???. Stock.measures: They are evaluated at particular moments in time. Examples
are the number of products in a warehouse, the number of inhabitants of a city,
the temperature measured by a gauge.
???. Unit.measures: They are evaluated at particular moments in time, but they
are expressed in relative terms. Examples are the unit price of a product, the
discount percentage, the exchange rate of a currency.
The aggregation operators that can be used on the three types of measures are summarized
in Table 3.
Pages:
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72