26 1 Hierarchies and Relationships
Striping was first introduced in the Resource Description Framework (RDF)
(Lassila and Swick 1999).Figure 1.14 Using striping to represent relationships involving the human insulin
gene. The shaded elements in the figure are the relationships that link a parent ele-
ment to its child elements.Another way to specify a relationship is to use areference. A reference is an
attribute of an XML element that refers to some other data. The referenced
data can be anything and anywhere, not just XML elements and not just in
the same XML document. This technique is much more flexible and powerful
than striping. An example of a molecule with two atoms bound to each other
is shown in figure 1.15. The two atoms in theatomArrayare referenced by
thebondin thebondArray. In general, a reference could be to anything that
has a URI.
Striping and references can be used in the same document. In RDF, the
two techniques can be used interchangeably, and they have exactly the same