With the latest quarterly update, the Terms box at the bottom of WebDewey schedule and table records was changed.  What, exactly, happened to the mapped LCSH within WebDewey? 

Although we now list three, rather than five, types of mapped LCSH on the right side of the Terms box, the mappings are the most up-to-date and accurate ones we have ever produced.  The three types are as follows: the EM (Editorially Mapped) subject headings that you are accustomed to seeing; new PPT (People, Places & Things) headings; and enhanced SM (Statistically Mapped) headings. 

Except for the fact that their number is increased each quarter, there has been no substantive change in the Editorially Mapped subject headings.  These headings are the result of the DDC editors' review of the LC Subject Headings Weekly Lists of new subject headings and selecting the Dewey number or numbers that is the best match for them.  The EMs also include mappings of older LCSH that the editors do in the course of their work updating the Classification. 

The PPT mappings were created in the course of work on the print publication, People, Places & Things.  These include updated NF mappings from previous versions of WebDewey, as well as more than half of the 50,000+ LCSH mappings that are in the new book.  All the PPT headings were either intellectually mapped to Dewey numbers by the editors or reviewed by the editors after being initially generated automatically. 

The SM column now contains all statistically mapped subject headings.  These were derived based on a new algorithm that combines and updates the algorithm used previously to generate the SM and FM headings.  We examine our statistical mapping algorithm on an ongoing basis, always with an eye toward improving its accuracy and currency. 

The newest mappings include such LCSH as September 11 Terrorist Attacks, 2001 (973.931), Food in popular culture (306.4), Third millennium--Forecasts (303.49), and Tap dance music (784.1887). 

Last revised: 04 March 2011