Celko Visitation Model

This class can be use to manipulate hierarchic trees of records stored in a MySQL database using Joe Celko visitation model. It can perform the following tasks in a very effecient way mostly using one SELECT query statement: - Find out leaf nodes in the current tree (nodes have no children) - Find out nodes of a sub-tree for given node - Find out the context path of given node - Find out the level or depth of a given node - Find out how many descendants a given node has