View source for Milestone-chunk.xquery

== Authorship ==
{| 
| ''Author''
| David Sewell, University of Virginia, [mailto:dsewell@virginia.edu dsewell@virginia.edu]
|- 
| ''Last revised''
| 2007-05-02
|-
| ''Previous version''
| none
|}


== Summary ==
This is an XQuery 1.0 function that will return all of the content between two milestone elements such as '''pb'''
while preserving the hierarchical structure of the containing elements. For example, given content like this in a TEI document:
<pre><nowiki>
<TEI>
  <text>
    <body>
      <div1 type="chapter" n="1"> <!-- lots of div2s -->
        <div2 xml:id="doc100">
          <p>An example<pb n="3"/>of a <i>very</i> short page<pb n="4"/>here.</p>
        </div2> <!-- followed by lots of other stuff -->
      </div1>
    </body>
  </text>
</TEI>
</nowiki></pre>

the function would produce the following XML fragment as output when asked to return content between '''pb/@n=3''' and '''pb/@n=4'''
with the '''text''' element as the ancestor:

<pre><nowiki>
  <text>
    <body>
      <div1 type="chapter" n="1">
        <div2 xml:id="doc100">
          <p><pb n="3"/>of a <i>very</i> short page</p>
        </div2>
      </div1>
    </body>
  </text>
</nowiki></pre>

In other words, the full hierarchical structure of the ancestor elements, including their attributes, is preserved, but only the nodal content between the milestons is included.

== Required Input ==

The function signature is
<pre><nowiki>
local:milestone-chunk(
  $ms1 as element(),
  $ms2 as element(),
  $node as node()*
)
</nowiki></pre>

'''$node''' is an element known to be a common ancestor of the two milestones. For example, it could be '''TEI/text''', or '''TEI/text/body''', or even '''TEI/text/body/div1[3]''' if the milestone parameters are both descendants of that div1.

'''$ms1''' is the first milestone element; '''$ms2''' is the second milestone element.

For example, the output in "Summary" above might have been produced by the call

<pre><nowiki>
  let $input := doc("mydoc.xml")/tei:TEI/tei:text
  return local:milestone-chunk($input//pb[@n="3"], $input//pb[@n="4"], $input)
</nowiki></pre>

If '''$input''' had been 
   doc("mydoc.xml")/tei:TEI/tei:text/tei:body
then the output would have started at the '''body''' element, etc.

'''$ms1''' and '''$ms2''' do not need to be adjacent milestones. You can, for example, return content between '''pb/@n=4''' and '''pb/@n=7'''. Nor do the milestones need to be of the same type; you can return content between the '''pb''' for page 4 and an arbitrary anchor or pointer element later in the document.

== Expected Output ==

As indicated in the example in "Summary" above, the output should be a single XML element reflecting the structure of the input ancestor element and its descendants, but otherwise containing only the nodal content between the two milestone elements in the original input.

== Known Restrictions or Problems ==
The output will contain a copy of the first milestone element, but not of the second (closing) one. This is a consequence of the need to use pseudo-milestones for the second milestone in some cases; see next paragraph. 

When using this function to generate content between TEI '''pb''' elements, an obvious problem is that the final page will not have a final '''pb''' milestone. In this case, use a pseudo-milestone such as the last node in the input element. For example, using the sample document in "Summary" above, the content of page 4 ("here.") would be output via the call
<pre><nowiki>
  let $input := doc("mydoc.xml")/tei:TEI/tei:text
  local:milestone-chunk($input//pb[@n="4"], ($input//node())[last()], $input)
</nowiki></pre>

If you use this function to recurse over all the '''pb''' elements in a document, you will need to use a strategy like this when '''$ms1''' has no following '''pb''' element.

The function will not gracefully handle invalid input, but will probably throw run-time errors. You should be sure that the parameters passed to it reflect actual milestone elements with a common ancestor.

== Code ==
<pre><nowiki>
declare function local:milestone-chunk(
  $ms1 as element(),
  $ms2 as element(),
  $node as node()*
) as node()*
{
  typeswitch ($node)
    case element() return
      if ($node is $ms1) then $node
      else if ( some $n in $node/descendant::* satisfies ($n is $ms1 or $n is $ms2) )
      then
        element { name($node) }
                { for $i in ( $node/node() | $node/@* )
                  return local:milestone-chunk($ms1, $ms2, $i) }
      else if ( $node >> $ms1 and $node << $ms2 ) then $node
      else ()
    case attribute() return $node (: will never match attributes outside non-returned elements :)
    default return 
      if ( $node >> $ms1 and $node << $ms2 ) then $node
      else ()
};
</nowiki></pre>

== Implementation in eXist ==
This function is implemented in [[eXist]] (as a function called [http://demo.exist-db.org/exist/functions/util/get-fragment-between util:get-fragment-between()]) by Josef Willenborg, Max Planck Institute for the History of Science [mailto:jwillenborg@mpiwg-berlin.mpg.de jwillenborg@mpiwg-berlin.mpg.de]:

<pre><nowiki>
util:get-fragment-between($beginning-node as node()?, $ending-node as node()?, $make-fragment as xs:boolean?) xs:string
</nowiki></pre>

Returns an xml fragment or a sequence of nodes between two elements (normally milestone elements). The $beginning-node represents the first node/milestone element, $ending-node, the second one. The third argument, $make-fragment, is a boolean value for the path completion. If it is set to true() the result sequence is wrapped into a parent element node. 

Example call of the function for getting the fragment between two TEI page break element nodes: 
<pre><nowiki>
let $fragment := util:get-fragment-between(//pb[1], //pb[2], true())
</nowiki></pre>

== Extended version which keeps the namespace decleration ==
<pre><nowiki>
declare function local:milestone-chunk-ns(
  $ms1 as element(),
  $ms2 as element(),
  $node as node()*
) as node()*
{
  typeswitch ($node)
    case element() return
      if ($node is $ms1) then $node
      else if ( some $n in $node/descendant::* satisfies ($n is $ms1 or $n is $ms2) )
      then
        (: element { name($node) } :)
           element {QName (namespace-uri($node), name($node))}
                { for $i in ( $node/node() | $node/@* )
                  return local:milestone-chunk-ns($ms1, $ms2, $i) }
      else if ( $node >> $ms1 and $node << $ms2 ) then $node
      else ()
    case attribute() return $node (: will never match attributes outside non-returned elements :)
    default return 
      if ( $node >> $ms1 and $node << $ms2 ) then $node
      else ()
};
</nowiki></pre>

[[Category:XQuery]]