Although Old Chinese is known from written records beginning around 1200 BC, the logographic script provides much more indirect and partial information about the pronunciation of the language than alphabetic systems used elsewhere.Several authors have produced reconstructions of Old Chinese phonology, beginning with the Swedish sinologist Bernard Karlgren in the 1940s and continuing to the present day.The method introduced by Karlgren is unique, comparing categories implied by ancient rhyming practice and the structure of Chinese characters with descriptions in medieval rhyme dictionaries, though more recent approaches have also incorporated other kinds of evidence.