 Several commentators have noted that personal identity is a strong theme in the book , and that it addresses issues of racism through the treatment of non @-@ magical , non @-@ human and non @-@ living characters . Some commentators regard the diary as a warning against uncritical acceptance of information from sources whose motives and reliability cannot be checked . Institutional authority is portrayed as self @-@ serving and incompetent . The book is also known to have some connections to the sixth novel of the series , Harry Potter and the Half @-@ Blood Prince . 
