The characterization ???local??? is because this predicate
includes restrictions only on Di and not on other dimension tables or the fact table.
This predicate is very important for the h-surrogate processing phase explained
later, and is used to produce the necessary h-surrogate specification accessing the
fact table discussed later.
The vast majority of OLAP queries contains an equality restriction on a number of
hierarchical attributes and more commonly on hierarchical attributes that form a
complete path in the hierarchy (i.e., starting from the most aggregated level to some
lower level without ???gaps??? in between). For example, the query ???show me sales for
area A in region B for each month of 1999??? contains two whole-path restrictions,
one for a dimension LOCATION and one for a DATE: (a) LOCATION.Region = ???A??™
AND LOCATION.Area = ???B??™ and (b) DATE.Year = 1999. This is reasonable since
the core of analysis is conducted along the hierarchies. We call this kind of restriction
hierarchical prefix path (HPP) restrictions. Note also that even if we impose a
restriction solely on an intermediate level hierarchical attribute, we can still have
an HPP restriction, as long as hierarchical attributes functionally determine higher
level ones. For example, the restriction Month = ???AUG-99??™ implies also that Year
= 1999.
Let us now define an example query on the schema of Figure 1: We want to see the
sum of sales by area and month for areas with population more than 1 million, for
SELECT
FROM , D , D , ??¦, Dk
WHERE
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