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