<?xml encoding="US-ASCII" ?>
<!-- ++++++++++++++++++++++++++++++++++++++++++++++++++++++++

     A DTD for storing the database of very simple hierarchical browsers.

     The tree structure is encoded using a list with references.
     It is easier to build up a proper accessor this way.

     ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ -->
<!ELEMENT hierarchy-browser (element-list,reference-tree)>

<!-- a hierarchy-browser has access to elements,
     in the browser the elements are stored as a hierarchy -->
<!ELEMENT element-list (element+)>
<!ELEMENT element EMPTY>
<!ATTLIST element image-id        CDATA #REQUIRED
                  image-location  CDATA #REQUIRED>
<!-- in the browser the elements are stored as a hierarchy 
     for saving memory and typing, the tree structure is
     only stored as a tree, in which every node contains
     the ID of the image wanted.
-->
<!ELEMENT reference-tree (reference-tree*)>
<!ATTLIST reference-tree  image-id CDATA #REQUIRED>

