when to use keys?

The burning question today at work is whether or not we should use keys in our
current project.  The problem is this.  We need to contruct an HTML navigation
menu based upon a user's credentials.  A JSP custom tag is using a Java class
to determine what credentials this user has, and returns those results as
XML.  So we have:

<menu-key>welcome.jsp</menu-key>
<menu-key>doSomething_1.jsp</menu-key>
<menu-key>doSomething_2.jsp</menu-key>
<menu-key>doSomething_3.jsp</menu-key>

This is available underneath the <root> node of this document, which means that
we know how to access it directly using XPath.  By "directly" I mean that we
don't need to do any time wasting XPath expressions like //menu-key.
  We also include a XML file with content like so:

<menu-item href="welcome.jsp">Home</menu-item>
<menu-item href="doSomething_1.jsp">Page 1</menu-item>
<menu-item href="doSomething_2.jsp">Page 2</menu-item>
<menu-item href="doSomething_3.jsp">Page 3</menu-item>
<menu-item href="doSomething_4.jsp">Page 4</menu-item>

The <menu-key>'s are the items which should be shown (according to our custom
tag) and the <menu-item>'s are all of the items which could be displayed if the
user had all of the necessary credentials (according to our static file,
menu.xml).
  So now the problem (which we have already solved) is to construct the menu in
HTML with the corresponding hyperlinks and menu text.
  Since we know exactly where both of these sets of data exist in the XML tree
is there any point in using keys?  We know where the <menu-key>'s are:
/root/menu-key, and we know where the <menu-item>'s are:
document('menu.xml')/menu-item.
  Can anyone see a benefit to using keys in this situation or would you
accomplish it by doing something like:

<xsl:for-each select="/root/menu-key">
 <xsl:variable name="current-item" select="."/>
  <a href="{.}"><xsl:value-of
select="document('menu.xml')/menu-item[@href=$current-item]"/></a>
</xsl:for-each>

Are keys primarily useful when you don't know where the data exists in the XML
tree, but you need quick and/or repetitive access to it?  Would there be any
large performance increase in using keys in this situation where we are
iterating through the list of <menu-key>'s?
  Thanks for your time,
   -M@

-- 
Matt Hixson
Aventail Corporation
Seattle, Washington


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