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4.2 Data Warehouse Modeling: Data Cube and OLAP 143

dimension location, mapping a set of low-level concepts (i.e., cities) to higher-level, more
general concepts (i.e., countries). This concept hierarchy is illustrated in Figure 4.9.
Many concept hierarchies are implicit within the database schema. For example,
suppose that the dimension location is described by the attributes number, street, city,
province or state, zip code, and country. These attributes are related by a total order,
forming a concept hierarchy such as “street < city < province or state < country.” This
hierarchy is shown in Figure 4.10(a). Alternatively, the attributes of a dimension may

location
all all

country Canada USA

province_ British Columbia Ontario New York Illinois
or_state

city Vancouver Victoria Toronto Ottawa New York Buffalo Chicago Urbana

Figure 4.9 A concept hierarchy for location. Due to space limitations, not all of the hierarchy nodes are
shown, indicated by ellipses between nodes.

country
year

province_or_state
quarter

city
month week

street day
(a) (b)

Figure 4.10 Hierarchical and lattice structures of attributes in warehouse dimensions: (a) a hierarchy for
location and (b) a lattice for time.