BO Algorithms

Traversal algorithm: While N the current node is not empty Do: If N's direct descendance has been modified: Find the nearest frozen ancestor, call it FA Apply the Frozen Node Algorithm to FA Let the new current node be FA's successor in preorder traversal Else let the new current node be N's successor in preorder traversal

Frozen Node Algorithm

1. For each child, C of FA do:
   1. If C is a leaf, Add C to a document list DL
   2. If C is non-frozen, Collapse C's subtree and Add all leaves to DL
   3. If C is frozen, Put it in a separate list, FDL.
2. Apply the Bookmark Clustering Algorithm on DL to form a new cluster hierarchy rooted at a new node NEW-FA
3. Apply the Frozen Node Algorithm on all elements of FDL and add them as children of NEW-FA
4. Replace FA by NEW-FA