Simple XML
Book XML File
<books>
  <book id="1">
    <title>The Grapes of Wrath</title>
    <author>John Steinbeck</author>
  </book>
  <book id="2">
    <title>The Pearl</title>
    <author>John Steinbeck</author>
  </book>
</books>
Book PHP File
<?php
$books 
simplexml_load_file('presentations/slides/intro/book.xml');

foreach (
$books->book as $book) {
  echo 
"{$book['id']}{$book->title} was written by {$book->author}<br>\n";
}
?>
Output
1. The Grapes of Wrath was written by John Steinbeck
2. The Pearl was written by John Steinbeck