= eXist Interface: Maintenance of user annotations =

User annotations are maintained by the interface function /mpdl/interface/external/object.xql. 
This function has 3 parameters:
* operation (possible values: read, create, update, delete)
* type (possible values: element, query)
* object (see examples below)
  * attributes
    * uid: user id (normally email address) of the operation (e.g. andy@mpiwg-berlin.mpg.de)
    * documentId: the eXist document identifier (e.g. /tei/en/Test_1789.xml)
    * xpointer: the xpointer to the position in that document (e.g.: id('page2')/TEI[1]/text[1]/body[1]/p[1]/s[3]/point(4)); see [/wiki/schema/xpointer XPointer specification]
  * value: if operation is create or update: the new object (e.g. <note>This is an annotation of Andy</note>)

== Examples ==

=== Example document ===
[http://mpdl-test.mpiwg-berlin.mpg.de:30030/mpdl/page-query-result.xql?document=/tei/en/Test_1789.xml&mode=text&pn=2 Test document with user annotations]

=== Read annotations ===
{{{
  http://mpdl-test.mpiwg-berlin.mpg.de:30030/mpdl/interface/external/object.xql?
    operation=read&
    type=element&
    object=<object documentId="/tei/en/Test_1789.xml" xpointer="id('page2')"></object>
}}}
[http://mpdl-test.mpiwg-berlin.mpg.de:30030/mpdl/interface/external/object.xql?operation=read&type=element&object=%3Cobject%20documentId=%22/tei/en/Test_1789.xml%22%20xpointer=%22id%28%27page2%27%29%22%3E%3C/object%3E Read annotations]

=== Create annotation ===
{{{
  http://mpdl-test.mpiwg-berlin.mpg.de:30030/mpdl/interface/external/object.xql?
    operation=create&
    type=element&
    object=<object uid="andy@mpiwg-berlin.mpg.de" documentId="/tei/en/Test_1789.xml" xpointer="id('page2')/TEI[1]/text[1]/body[1]/p[1]/s[3]/point(4)"><note>This is an annotation of Andy</note></object>
}}}
[http://mpdl-test.mpiwg-berlin.mpg.de:30030/mpdl/interface/external/object.xql?operation=create&type=element&object=%3Cobject%20uid=%22andy@mpiwg-berlin.mpg.de%22%20documentId=%22/tei/en/Test_1789.xml%22%20xpointer=%22id%28%27page2%27%29/TEI%5B1%5D/text%5B1%5D/body%5B1%5D/p%5B1%5D/s%5B3%5D/point%284%29%22%3E%3Cnote%3EThis%20is%20an%20annotation%20of%20Andy%3C/note%3E%3C/object%3E  Create annotation]

=== Delete annotation ===
{{{
  http://mpdl-test.mpiwg-berlin.mpg.de:30030/mpdl/interface/external/object.xql?
    operation=delete&
    type=element&
    object=<object uid="andy@mpiwg-berlin.mpg.de" documentId="/tei/en/Test_1789.xml" xpointer="id('page2')/TEI[1]/text[1]/body[1]/p[1]/s[3]"></object>
}}}
[http://mpdl-test.mpiwg-berlin.mpg.de:30030/mpdl/interface/external/object.xql?operation=delete&type=element&object=%3Cobject%20uid=%22andy@mpiwg-berlin.mpg.de%22%20documentId=%22/tei/en/Test_1789.xml%22%20xpointer=%22id%28%27page2%27%29/TEI%5B1%5D/text%5B1%5D/body%5B1%5D/p%5B1%5D/s%5B3%5D%22%3E%3C/object%3E  Delete annotation]

== Limitations ==
* Interface
  * Java: no real user test done
  * Display of a document page with external objects (insertExternalElements.xsl): full redesign and new implementation
* Bugs
  * at one position there could be only one external user annotation so far (bug in XSL script)