Thomson Reuters. Derwent World Patents Index (DWPI). DWPI Classification. Edition 5. London: Published by Thomson Reuters, published December 2014, © 2015. 61 s. ISBN 978-1-908083-21-0.
Dostupné také volně ze školícího webu producenta: http://ip-science.thomsonreuters.com/m/pdfs/DWPI_Class_Manual_2015.pdf.