In PHP è semplice generare un documento XML a partire dai risultati di una query al database.
La soluzione è la seguente:
require_once('db-functions.php');
header('Content-Type: text/xml; charset=UTF-8');
$products = get_results('SELECT id, title, price FROM products WHERE price > 0.00 ORDER BY price LIMIT 6');
$xml = new DOMDocument('1.0', 'UTF-8');
$xml_products = $xml->createElement('Products');
foreach($products as $product) {
$xml_product = $xml->createElement('Product');
$id = $xml->createElement('ID', $product['id']);
$title = $xml->createElement('Title', ucwords($product['title']));
$price = $xml->createElement('Price', $product['price']);
$xml_product->appendChild($id);
$xml_product->appendChild($title);
$xml_product->appendChild($price);
$xml_products->appendChild($xml_product);
}
$xml->appendChild($xml_products);
echo $xml->saveXML();