Most days, OCLC's Duplicate Detection and Resolution (DDR) software runs behind the scenes of WorldCat, searching for and merging duplicate bibliographic records.  There are, however, several categories of records that are deliberately exempted from DDR processing.  Among those exempted categories are all records with dates of publication up and to and including 1829, and all records identified in field 040 subfield $e as being cataloged under any of the descriptive cataloging conventions commonly used for rare and archival materials.  OCLC determined these specifications in consultation with the Bibliographic Standards Committee<https://rbms.info/committees/bibliographic_standards/> (BSC) of the Rare Books and Manuscripts Section<https://rbms.info/> (RBMS) of the Association of College and Research Libraries<http://www.ala.org/acrl/> (ACRL), a division of the American Library Association<http://www.ala.org/> (ALA).
OCLC is pleased to announce that the following seven MARC Description Convention Source Codes<https://www.loc.gov/standards/sourcelist/descriptive-conventions.html> that are appropriate for rare and archival materials have now been added to the existing list of 25 exempted codes.

  *   dcarlisnaaf -- Best Practices for Cataloging Artist Files Using MARC<http://artistfiles.arlisna.org/best-practices-for-cataloging-artist-files-using-marc/> (ARLIS)
  *   dcrmr -- Descriptive Cataloging of Rare Materials (RDA Edition)<https://bsc.rbms.info/DCRMR/> Chicago: Rare Books and Manuscripts Section of the Association of College and Research Libraries)
  *   fiafcm -- FIAF moving image cataloguing manual<https://www.fiafnet.org/pages/E-Resources/Cataloguing-Manual.html> (International Federation of Film Archives)
  *   hmstcn -- Handleiding voor de medewerkers aan de STCN ('s Gravenhage: Koninklijke Bibliotheek) [Short title catalog of the Netherlands]
  *   kam -- Pravilnik za opis i pristup gradji u knjiznicama, arhivima i muzejima<https://pravilnik.kam.hr> (Zagreb: Hrvatski drzavni arhiv : Muzejski dokumentacijski centar : Nacionalna i sveucilisna knjiznica u Zagrebu)
  *   nmxcmdf -- Norma Mexicana NMX-R-069-SCFI-2016: Documentos Fotográficos-Lineamientos para su Catalogación<http://fotobservatorio.mx/norma_mexicana.html> (México. Secretaría de Economía. Dirección General de Normas)
  *   rnab -- Ressourcenerschließung mit Normdaten in Archiven und Bibliotheken (RNAB) für Personen-, Familien-, Körperschaftsarchive und Sammlungen
Most of these seven codes are relatively recent additions to the MARC Description Convention Source Codes list.
The complete list of 32 MARC Description Convention Source Codes that are now exempt from DDR processing in WorldCat when they appear in field 040 subfield $e are:

     *   amim
     *   amremm
     *   appm
     *   bdrb
     *   cco
     *   cgcrb
     *   dacs
     *   dcarlisnaaf
     *   dcgpm
     *   dcrb
     *   dcrmb
     *   dcrmc
     *   dcrmg
     *   dcrmm
     *   dcrmmss
     *   dcrmr
     *   dcrms
     *   dmbsb
     *   enol
     *   estc
     *   fiafcm
     *   gihc
     *   hmstcn
     *   iosr
     *   kam
     *   nmxcmdf
     *   ohcm
     *   rad
     *   rna
     *   rnab
     *   vd16
     *   vd17
The full citations for all the codes, and links to many of the descriptive conventions themselves, may be found in the MARC Description Convention Source Codes<https://www.loc.gov/standards/sourcelist/descriptive-conventions.html> document maintained by the Library of Congress.
jay
--
Jay Weitz
(he/him/his)
OCLC · Senior Consulting Database Specialist, Membership and Research
6565 Kilgour Place, Dublin, Ohio USA 43017
T +1-614-764-6156 · T +1-800-848-5878 x6156 · F +1-614-718-7195
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