function createXMLfile($booksArray){
  
   $filePath = 'book.xml';

   $dom     = new DOMDocument('1.0', 'utf-8'); 

   $root      = $dom->createElement('books'); 

   for($i=0; $i<count($booksArray); $i++){
     
     $bookId        =  $booksArray[$i]['id'];  

     $bookName      =   htmlspecialchars($booksArray[$i]['title']);

     $bookAuthor    =  $booksArray[$i]['author_name']; 

     $bookPrice     =  $booksArray[$i]['price']; 

     $bookISBN      =  $booksArray[$i]['ISBN']; 

     $bookCategory  =  $booksArray[$i]['category'];  

     $book = $dom->createElement('book');

     $book->setAttribute('id', $bookId);

     $name     = $dom->createElement('title', $bookName); 

     $book->appendChild($name); 

     $author   = $dom->createElement('author', $bookAuthor); 

     $book->appendChild($author); 

     $price    = $dom->createElement('price', $bookPrice); 

     $book->appendChild($price); 

     $isbn     = $dom->createElement('ISBN', $bookISBN); 

     $book->appendChild($isbn); 
     
     $category = $dom->createElement('category', $bookCategory); 

     $book->appendChild($category);
 
     $root->appendChild($book);

   }

   $dom->appendChild($root); 

   $dom->save($filePath); 

 }