Datasheet

<book>

<title>Amazon.com Mashups</title>

<author>Francis Shanahan</author>

</book>

<book>

<title>Yahoo! Maps Mashups</title>

<author>Charles Freedman</author>

</book>

</books>

Every XML document must start with a header that declares it as XML:

<?xml version=”1.0”?>

The header is then followed by a single root element— in this case <books>. Within the root element sits

the rest of the document. In the example here, the

<books> element contains a list of individual <book>

elements. Each <book> element contains, in turn, <title>, <author>, and <isbn> elements.

XPath, or

XML Path Language, enables you to address different parts of an XML document. It is a very

powerful tool often used in processing and manipulating XML. XPath treats an XML document as a tree

of nodes, with each element and each attribute represented by a node in that tree. An

XPath query returns

a set of nodes from the tree. A typical XPath query consists of an expression representing the path to one

or more nodes. So, for example, in the sample XML document here, the XPath query

/books

will return the root <books> node, while the query

/books/book

returns the set of <book> nodes contained within <books>, and

/books/book/title

returns the set of <title> nodes.

To return the third book in the list, you would use the following XPath query:

/books/book[3]

And the last book could be found with

/books/book[last()]

If you don’t want to specify the whole path to an element, you can use the following notation:

//title

— which in this example will return all the <title> nodes within the document — regardless of location.

Part I: Building a New Internet

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