Thomson Reuters. Derwent World Patents Index (DWPI). DWPI Classification. Edition 4. London: Published by Thomson Reuters, published December 2011, © 2012. 58 s. ISBN 978-1-908083-09-8.
Dostupné také volně ze školícího webu producenta: http://ip-science.thomsonreuters.com/m/pdfs/DWPI_Class_Manual_2014.pdf.