XML in a Nutshell, 3rd Edition

XML Trees

Let’s look at a slightly more complicated XML document. Example 2-2 is a person element that contains more information suitably marked up to show its meaning.

Example 2-2. A more complex XML document describing a person

<person>
  <name>
    <first_name>Alan</first_name>
    <last_name>Turing</last_name>
  </name>
  <profession>computer scientist</profession>
  <profession>mathematician</profession>
  <profession>cryptographer</profession>
</person>

Parents and children

The XML document in Example 2-2 is still composed of one person element. However, now this element doesn’t merely contain undifferentiated character data. It contains four child elements: a name element and three profession elements. The name element contains two child elements of its own, first_name and last_name.

The person element is called the parent of the name element and the three profession elements. The name element is the parent of the first_name and last_name elements. The name element and the three profession elements are sometimes called each other’s siblings . The first_name and last_name elements are also siblings.

As in human society, any one parent may have multiple children. However, unlike human society, XML gives each child exactly one parent, not two or more. Each element (with one exception we’ll note shortly) has exactly one parent element. That is, it is completely enclosed by another element. If an element’s start-tag is inside some element, then its end-tag must also be inside that element. Overlapping ...