Previously I posted on something related to primary key and foreign key used in schema to maintain the relationship for my xml documents. I am still trying to sort that problem out :X
I moved on to try to create a schema for my nested menu. It takes me quite sometimes to find the correct solution for my schema to validate my xml file. But the time is worth it 
XML:
<menu>
<menuItem name="Profile" link="" xmlPath="user.xml" xslPath="profile.xsl" title="Profile"/>
<menu name="Idea" link="" xmlPath="idea/idea.xml" xslPath="idea/idea.xsl" title="Idea" >
<menuItem name="Post New Idea" link="idea/postNewIdea.php" xmlPath="" xslPath="i" title="Post New Idea" />
<menuItem name="My Idea" link="" xmlPath="idea/idea.xml" xslPath="idea/myIdea.xsl" title="My Idea" />
</menu>
<menuItem name="Comment" link="" xmlPath="comment/comment.xml" xslPath="comment/comment.xsl" title="Comment"/>
<menuItem name="Customize New Menu" link="../menu/addMenu.php" xmlPath="" xslPath="" title="Customize new Menu"/>
<menuItem name="Logout" link="../logout.php" title="Logout"/>
</menu>
</menus>
Schema:
<xsd:complexType>
<xsd:sequence maxOccurs="unbounded">
<xsd:element ref="menu" minOccurs="0" />
</xsd:sequence>
</xsd:complexType>
</xsd:element>
<xsd:element name="menu">
<xsd:complexType >
<xsd:sequence minOccurs="0" maxOccurs="unbounded">
<xsd:element name="menuItem"/>
<xsd:element ref="menu" minOccurs="0"/>
</xsd:sequence>
<xsd:attribute name="name" type="xsd:string"></xsd:attribute>
<xsd:attribute name="link" type="xsd:string"></xsd:attribute>
<xsd:attribute name="xmlPath" type="xsd:string"></xsd:attribute>
<xsd:attribute name="xslPath" type="xsd:string"></xsd:attribute>
<xsd:attribute name="title" type="xsd:string"></xsd:attribute>
</xsd:complexType>
</xsd:element>
<xsd:element name="menuItem">
<xsd:complexType>
<xsd:attribute name="name" type="xsd:string"></xsd:attribute>
<xsd:attribute name="link" type="xsd:string"></xsd:attribute>
<xsd:attribute name="xmlPath" type="xsd:string"></xsd:attribute>
<xsd:attribute name="xslPath" type="xsd:string"></xsd:attribute>
<xsd:attribute name="title" type="xsd:string"></xsd:attribute>
</xsd:complexType>
</xsd:element>
Note: I have problem in self-referencing when I try to use menu as my root, then I create a new “menus” root so my “menu” element can perfectly reference to itself. I also tried to use xsd:all or xsd:any but the validator complaining about some item like nested “menu” or “menulist” should not existed. I give up on using both method and just stick to xsd:sequence.
Xsl:
<xsl:if test="@name">
<a href="#blank">
<div><xsl:attribute name="onclick">xajax_openPage('<xsl:value-of select="./@xmlPath"/>','<xsl:value-of select="./@xslPath"/>', '<xsl:value-of select="./@link"/>', '<xsl:value-of select="./@title"/>')</xsl:attribute>
<xsl:value-of select="./@name"/></div></a>
</xsl:if>
<table>
<xsl:for-each select="./child::*">
<tr><td><xsl:apply-templates select="." />
</td></tr>
</xsl:for-each>
</table>
</xsl:template>
<xsl:template match="menuItem">
<a href="#blank">
<div><xsl:attribute name="onclick">xajax_openPage('<xsl:value-of select="./@xmlPath"/>','<xsl:value-of select="./@xslPath"/>', '<xsl:value-of select="./@link"/>', '<xsl:value-of select="./@title"/>')</xsl:attribute>
<xsl:value-of select="./@name"/></div></a>
</xsl:template>
Above xsl is the way I render the document to xHTML. In the xsl document, I render the element recursively.