A Gentle Introduction to xml

For trees of unknown depth we must sometimes use recursive routines to extract data. We have such a file in yahoo.xml which, as you might imagine, could be pretty deep.

The function walkover takes a node n as input. The other parameter x gives the depth of the node. We visit each node, then visit each if the children in turn. This is a "pre-order" walk. We visit the parent before we visit the children.

• Try out the example - note that the number equals the depth of the node. Get the program to print this value. Like this.
• You can use the expression "--------".substring(0,i) to generate a string of -, try writing this instead of the number i. Like this.

This time the s parameter builds up the path of the node so far.

• The id is part of the yahoo address of the relevant page. For example http://dir.yahoo.com/Science/Astronomy/Cosmology/ Note that the terms Science, Astronomy and Cosmology are given as the id attributes for the corresponding nodes. Use this to create linked words. Like this