Conceptual Data Warehouse Design - Data Warehouse Systems: Design and Implementation - page 99

City

CityName
CityPopulation
CityArea
...

Employee

State

EmployeeID
FirstName
LastName
Title
BirthDate
...

StateName
EnglishStateName
StateType
...

Territory

TerritoryName
Description

Fig. 4.12 Parallel dependent hierarchies leading to different parent members of the
shared level

the sales of all employees to the State level following the Lives hierarchy gives
a total amount of $300, whereas the corresponding value will be equal to $150
when the Territories hierarchy is traversed. Note that both results are correct,
since the two hierarchies represent different analysis criteria.

4.2.6 Nonstrict Hierarchies

In the hierarchies studied so far, we have assumed that each parent-child
relationship has a one-to-many cardinality, that is, a child member is related
to at most one parent member and a parent member may be related to several
child members. However, many-to-many relationships between parent and
child levels are very common in real-life applications. For example, a diagnosis
may belong to several diagnosis groups, 1 week may span 2 months, a product
may be classified into various categories, etc.
A hierarchy that has at least one many-to-many relationship is called
nonstrict ; otherwise, it is called strict . The fact that a hierarchy is strict
or not is orthogonal to its kind. Thus, the hierarchies previously presented
can be either strict or nonstrict. We next analyze some issues that arise when
dealing with nonstrict hierarchies.

State Georgia Florida

City ... Atlanta Orlando Tampa ...

Janet
Leverling

Employee

Fig. 4.13 Examples of instances of the nonstrict hierarchy in Fig. 4.2