Here is a process to read a PMML file created by RapidMiner.
The PMML file in this case is a model created by running a decision tree algorithm on the iris data set. Here's a snapshot - the highlighted parts are to help explain later.
Next the process turns the documents into an example set and the number of rows in this corresponds to the number of times the SimplePredicate XPath query cut the file into smaller documents. The example set is returned and after some processing the final output is a list of the attributes used in the decision tree.
In the example, attributes a3 and a4 can be seen on the decision tree and these are also output as an example set.