Designing Data Marts from XML and Relational Data Sources - Data Warehousing Design and Advanced Engineering Applications - page 63

Figure 2. An example of DTD for e-Ticket documents

Recall that an ENTITY is a variable used to define
shortcuts for either commonly used text, or text
that is difficult to type.
Finally, the third simplification step applies
a set of transformations to the DTD to reduce
the components of its ELEMENT declarations.

Our transformations slightly differ from those
presented in (Shanmugasundarma, Tufte, Zhang,
DeWitt, & Naughton, 1999) and (Yan, & ADA,
2001) and resemble the transformations in (Jensen,
Møller, & Pedersen, 2001). They are of the three
types depicted in Figure 4: