White, and that a new
customer O??™Hara has been acquired and assigned to Mr. Black, when computing
the agent commissions all invoices for Smith are attributed to Mr. White,
while only invoices for O??™Hara are attributed to Mr. Black.
???. Yesterday.for.today: All events are referred to some past configuration of
hierarchies. In the previous example, all invoices for Smith are attributed to
Mr. Black, while invoices for O??™Hara are not considered.
???. Today.or.yesterday.(or.historical.truth): Each event is referred to the con-
figuration hierarchies had at the time the event occurred. Thus, the invoices
for Smith up to 2004 and those for O??™Hara are attributed to Mr. Black, while
invoices for Smith from 2005 are attributed to Mr. White.
While in the agent example, dynamicity concerns an arc of a hierarchy, the one
expressing the many-to-one association between customer and agent, in some cases
it may as well concern a dimension attribute: for instance, the name of a product
category may change. Even in this case, the different scenarios are defined in much
the same way as before.
On the conceptual schema, it is useful to denote which scenarios the user is interested
for each arc and attribute, since this heavily impacts on the specific solutions to be
adopted during logical design. By default, we will assume that the only interesting
scenario is today for yesterday??”it is the most common one, and the one whose
Figure 7.
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