Simple links are similar to HTML links, which are formed using the element A in HTML.

Simple links are used to jump from one source document to specified destination either within the same document or another document. Simple links have only one locator and hence move in one direction from source to target location. A Simple link contains a piece of text that acts as a resource, one end of the link.

An example for giving a simple link in a XML document is given here.

<sample.link xlink:form="sample" href="http:// m.com/title.XML" >see also
<sample.link>

Extended links allow us to link together any number of resources resulting in multiple targets instead of a simple one-to-one links in HTML.

Extended links allow XML documents to link to and from resources that cannot contain the links themselves. This includes graphic files, sound files, read-only documents and so on, which does not allow us to modify the contents or embed links.

They enable manipulations like filtering, addition and modification of links. For instance, imagine that we are able to modify the links at a certain point, so experienced readers of a technical manual can traverse a different path from that of novice readers.

Extended links also enable application software to process the links in different ways depending upon the requirements. An extended link does not directly point to anything or link anything together.

An extended link element identifies itself through its xlink:form attribute value and contains a set of locator elements that together form the extended link as shown. Here the comment element declares itself to be an extended link and an opinion element declares itself to be a locator element.

<comment xlink:form="extended">
          <opinion xlink:form="locator" href="link1"/>
          <reference href="#division1"/>
          <reference href="http://one.com/ first.html ">
          <reference href="references.htm"/>
</comment>

Links can be located in external documents. This is accomplished through the use of extended link groups.Similar to that of an extended link, an extended link group does not point or link to anything. Instead it contains a set of document elements, in which each document contains the link resources as shown.

<xternal.refs >
<ref.doc href="http:// first.com/one.html"/>
<ref.doc href="list.htm"/>
</xternal.refs>

When using extended link groups, there is a possibility of link element pointing to extended link group. If extended link group points back to the original document, or to a document containing another extended link group, then it would lead to infinite loops and links. To prevent the infinite linking, we can declare a value for the steps attribute of the group element. This specifies the limit of the number of layers that can be nested.

Extended links may be Inline extended link or Out-of-line extended links. By default, all link elements are Inline extended links. Extended links may be embedded in one of the resources participating in an extended link.

	An inline link is an internal link; that is completely within the current document.
	An out-of-line link refers to an external file that contains the link and target resource information.

<para id="para4">This is an
              <xref.list> example of
                       <see.also href="health.xml"/>
                       <see.also href=http://www.lifeline.com/defs.htm"/>
                       <see.also href="sample"/>
                       <xref.list>
              <xref.list> presented by …
</para>

Here is an example of an inline extended link. Here the xref.list element contains character data that serves as part of the associative trail formed by the links. Therefore the link element framed in the official terms of the X-Link specification contains a local resource of the link.

<xref.list>
        <see.also href="sample"/>
        <see.also href=health.xml"/>
        <see.also href="http://www.lifeline.com/defs.htm"/>
        <see.also href="sample"/>
</xref.list>

</para id="sample">
presented by ….</para>

Here is an example of out-of-line extended links. When the extended link is out-of-line link, it is no longer located in the same place as the link resources. It contains a pointer to the local link resource rather than the local link resource itself.

The figure shown here depicts the Inline extended link.

The type of the link, inline or out-of-line, does not specify the details like whether the link is located within the document or not.

Out-of-line links are particularly useful for extended link groups, which are a particular type of extended link.

A special type of <xlink:extended > element is used to indicate to an X-Link aware processor that out-of-line link exists for a particular document. Their role attribute should be set to xlink:external-linkset. The locator sub-elements, define external XML documents that contains the link and target locations.

<xlink:extended
       xmnls:xlink = "http:// www.w3.org/1999/xlink/namespace/"
       role="xlink:external-linkset">
<xlink:locator
       href="http: // www.wrox.com/Catalog/linkdb.xml"
       role="linkdatabase"
       title="Out-of-line catalog links" />
<xlink:extended>

Here is an example for out-of-line extended link using link databases. When Xlink-aware processor encounters the role attribute set to xlink:external-linkset, it reads the documents indicated in the locator sub-elements of the extended link that reference the document being processed.