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Chapter 16: A Brief XML Primer
Elements can also contain attributes (which we’ll look at shortly) as part of the opening (but not the closing)
tag for the element. Finally, elements can contain other elements, but, if they do, the inner element
must be closed before closing the outer element:
We will come back to elements shortly when we look at what it means to be well formed.
Nodes
When you map out the hierarchies that naturally form in an XML document, they wind up taking on the
familiar tree model that you see in just about any hierarchical relationship, illustrated in Figure 16-2.
Each intersection point in the tree is referred to as a node.
A secondary Node.
This is the immediate
child of the root node.
There can be zero,
one, or many of these.
Example: Customers
Another Node. A child of
the one above.
Example: Orders
(Customers have
Orders)
Figure 16-2
Another Node. A child of
the one above.
Example: Line Items
(Orders have line items)
Root Node. There
must be one and
only one. It is
often called
“root”, but doesn’t
have to be.
The contents of an XML document can be navigated based on node levels and the values in the attributes
and elements of particular nodes.
The “Root” Node
Perhaps one of the most common points of confusion in XML documents is over what is called the root
node. Every XML document must have exactly one (no more, no less) root node. The root node is an element
that contains any other elements in the document (if there are any). You can think of the root node
as being the unification point that ties all the nodes below it together and gives them structure within
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