Examples
Dimension constraints are statements that specify categories and paths allowed in the
structures of the elements of a dimension. We will illustrate the flavor of dimension
constraints using the dimension of Figure 4. Observe that every product element of
this dimension has the categories Brand and ElectricalCategory appearing together
or not appearing at all. This can be expressed with the following constraint:
??©Product,Brand??? ?‡” ??©Product,ElectricalCategory???.
This constraint is a statement that holds for all elements at the category Product,
which is the root category of the constraint. As an example, if we take the element
p1 and replace it in the constraint we obtain the expression:
??©p1,Brand??? ?‡” ??©p1,ElectricalCategory???,
0 Hurtado & Gutierrez
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which means that p1 has an ancestor in Brand if and only if p1 has an ancestor in
ElectricalCategory. So the constraint allows to discard the structures in which Brand
and MusicCategory do not appear together. This is important, since if we generalize
the dimension of Figure 4 to have n different categories instead of just four, there
might be 2n ??“ 1 possible structures (one for each nonempty subset of categories).
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