Create Simple XML Class

I need a class that reads in xml data from a database. And then allows the user easy access to the information using the following functions: table($name) get($name) where($condition) update() table - Returns a list of children that can be accessed by get to get their attributes. get - Returns a child's attribute. where - Acts on a table to reduce the rows in that table by a given condition. update - Forces the class to re-download the xml data from the database. There are a few special features that this class should have. 1) It should only load a tables data once unless the update function is called. 2) The get function should recognize when a child is a foreign key and then correctly link to the appropriate table's data. 3) The where function should be able to parse relatively complicated conditions with == =< => < > != ! && || in ( ) inputs. I have attached an outline zoho_database class, an example php file, and two example xml files. I have not tested these files so they may contain small errors.