XLink Example

Let's try to learn some basic XLink syntax by looking at an example.

The XML Example Document

Look at the following XML document, "bookstore.xml", that represents a few books:

<?xml version="1.0" encoding="ISO-8859-1"?>

<bookstore xmlns:xlink="http://www.w3.org/1999/xlink">

<book title="Harry Potter">
  <description
  xlink:type="simple"
  xlink:href="http://book.com/images/HPotter.gif"
  xlink:show="new">
  As his fifth year at Hogwarts School of Witchcraft and
  Wizardry approaches, 15-year-old Harry Potter is.......
  </description>
</book>

<book title="XQuery Kick Start">
  <description
  xlink:type="simple"
  xlink:href="http://book.com/images/XQuery.gif"
  xlink:show="new">
  XQuery Kick Start delivers a concise introduction
  to the XQuery standard.......
  </description>
</book>

</bookstore>

View the "bookstore.xml" file in your browser

In the example above the XLink namespace is declared at the top of the document (xmlns:xlink="http://www.w3.org/1999/xlink"). This means that the document has access to the XLink attributes and features.

The xlink:type="simple" creates a simple "HTML-like" link. You can also specify more complex links (multidirectional links), but for now, we will only use simple links.

The xlink:href attribute specifies the URL to link to, and the xlink:show attribute specifies where to open the link. xlink:show="new" means that the link (in this case, an image) should open in a new window.

XLink - Going Further

In the example above we have only demonstrated simple links. XLink is getting more interesting when we want to access remote locations as resources, instead of standalone pages. The <description> element in the example above sets the value of the xlink:show attribute to "new". This means that the link should open in a new window. We could have set the value of the xlink:show attribute to "embed". This means that the resource should be processed inline within the page. When you consider that this could be another XML document and not just an image, you could, for example, build a hierarchy of XML documents.

With XLink, you can also specify WHEN the resource should appear. This is handled by the xlink:actuate attribute. xlink:actuate="onLoad" specifies that the resource should be loaded and shown when the document loads. However, xlink:actuate="onRequest" means that the resource is not read or shown before the link is clicked. This is very handy for low-bandwidth settings.

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