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The Library of Congress > Cataloging, Acquisitions > PCC > NACO > Authority File Comparison Rules (NACO Normalization)

Based on the report of the Task Group on Normalization of the PCC Standing Committee on Automation, approved by the PCC Policy Committee in November 2007 and further revised April 1, 2009.

When a new authority record is added to an authority file, each heading is compared against the headings and references already in the file to determine whether the new headings and references are allowable, that is, adequately differentiated from existing headings. The headings and references already in the file and the ones to be added are normalized before comparison so that only certain characters will be considered in the comparison.  The normalization rules that apply to characters are specified in Appendix A. The rules for heading comparison are given below.

Rules for Comparison

Note the following before applying the rules for comparison:

  1. The following rules apply after characters have been subjected to the character normalizations described in Appendix A.
  2. The rules apply to all name authority records that are part of the NACO program: names, corporate bodies, meetings, etc., titles/series, and name/titles.  Name authority records, however, are not compared against subject authority records.
  3. The rules apply to LCSH subject authority records (008/11=a) that represent established headings (008/09=a) and subdivisions (008/09=d).  LCSH subject authority records, however, are not compared against name authority records. 
  4. For the purposes of these rules, 1XX fields in LCSH subject authority records for untraced and traced references (008/09=b or c) are not treated as established headings but as see references, so they should be regarded as 4XX fields in the comparisons below. 
  5. LC subject headings for children’s literature (008/11=b) or records from other subject heading systems are excluded from these comparisons.
  6. Established heading linking entries (7XX fields) are not compared.
  7. Except as noted in 6) below, the tags of the fields do not form part of this comparison, but subfield delimiters and codes are included.  Certain subfields (i.e., $i and $w in 4XX and 5XX) are eliminated before comparison.
  1. An established heading (1XX field) must not compare the same as any other established heading, except: an established topical heading (150 field) in one subject authority record may compare the same as an established form/genre heading (155 field) in another subject authority record.
  2. A see reference tracing (4XX field) must not compare the same as any established heading (1XX field) in any record.
  3. A see reference tracing (4XX field) must not compare the same as any see also reference tracing (5XX field) in any record.
  4. A see reference tracing (4XX field) must not compare the same as another see reference tracing (4XX field) in the same authority record.
  5. A see reference tracing (4XX field) in one authority record may compare the same as a see reference (4XX field) in another authority record.
  6. A see also reference tracing (5XX field) must have the same second and third tag characters and compare the same as an established heading in another authority record.  For example, a 500 field in one authority record must match a 100 field in another authority record.  This rule means that every 5XX field must have a matching 1XX field, but not all 1XX fields will have a matching 5XX field.

Notable Changes in this Revision

  1. Subfield codes are now considered as part of the comparison.  This allows the same term in a 150$a and 180$x to occur without conflict because the subfield codes ‘a’ and ‘x’ will make the strings unique.
  2. A see reference tracing (4XX field) may not compare the same as a see reference tracing (4XX field) in the same authority record; this was allowed under the earlier rules, although the practice wasn’t followed in LCSH records.

Appendix A

Note: The characters referred to below correspond to the MARC 21 Latin-based character sets, Basic Latin (ASCII) and Extended Latin (ANSEL).

Character Normalization Tables

General Characters

Character Character Comments
Leading blanks Delete  
Trailing blanks Delete  
Multiple blanks Delete/Blank Compress to a single blank
Lowercase letters Uppercase equivalent  
Uppercase letters Retain  
Numbers Retain  

Modifying Diacritics

Character Character Comments

Circle above, angstrom
Circle below
Dot below
Double acute
Dot below
Double tilde (first/second half)
Double underscore
High comma centered
High comma off center
Left hook
Ligature (first/second half)
Pseudo question mark
Right cedilla
Right hook, ogonek
Superior dot
Umlaut, diaeresis

Delete *Do not confuse with spacing character equivalents (see Other Special Characters below)

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Translated Characters

Character Character Comments
Superscript numbers Numbers Convert to non-superscript equivalent
Subscript numbers Numbers Convert to non-subscript equivalent
Diagraph AE AE Upper and lower case
Diagraph OE OE Upper and lower case
D with crossbar D Upper and lower case
Eth D Upper and lower case
Lowercase Turkish i I  
Polish L L Upper and lower case
Script small L L  
O Hook O Upper and lower case
U Hook U Upper and lower case
Scandinavian O O Upper and lower case
Icelandic Thorn TH Upper and lower case
Eszett symbol SS Do not use in NACO records
Greek alpha Uppercase Greek alpha
(U + 0391)
Do not use in NACO 1XX fields
Greek beta Uppercase Greek beta
(U + 0392)
Do not use in NACO 1XX fields
Greek gamma Uppercase Greek gamma
(U + 0393)
Do not use in NACO 1XX fields

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Character Character Comments
Exclamation mark Blank  
Quotation mark Blank  
Apostrophe Delete  
Opening parenthesis Blank  
Closing parenthesis Blank  
Hyphen, minus- Blank  
Opening square bracket Delete  
Closing square bracket Delete  
Opening curly bracket Blank  
Closing curly bracket Blank  
Less-than sign Blank  
Greater-than sign Blank  
Semicolon Blank  
Colon: Blank  
Period, decimal point Blank  
Question mark Blank  
Inverted question mark Blank  
Inverted exclamation mark Blank  
comma Comma or blank The first comma in $a is retained; all other converted to blank

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Other Special Characters

Character Character Comments
Music flat sign Retain  
Number sign Retain  
Slash Blank  
Reverse slash Blank  
Commercial at sign Retain  
Ampersand Retain  
Asterisk Blank  
Vertical bar (fill) Blank  
Percent Blank  
Equals sign Blank  
Plus sign Retain  
Plus or minus Blank  
Superscript plus, minus Blank  
Patent mark Blank  
Sound recording copyright Blank  
Copyright sign Blank  
Dollar sign Retain  
British pound Retain  
Degree sign Blank  
Spacing circumflex Blank  
Spacing underscore Blank  
Spacing grave Blank  
Spacing tilde Blank  
Euro sign Retain Do not use in NACO records
Music sharp sign Retain  
Alif Delete  
Ayn Delete  
Hard sign Delete  
Soft sign Delete  
Middle dot Blank  

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Content Designation

Character Character Comments
Indicators Delete  
Subfield delimiters Retain  
Subfield codes Retain  
Tag   See comparison rules
Joiner, Non-joiner, Unicode Formatting Characters Delete  

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Changes in this Revision

Character Old Conversion New Conversion
Commercial at sign Blank Retain
Vertical bar Delete Blank
Dollar sign Blank Retain
British pound sign Blank Retain
Middle dot Delete Blank
Greek alpha A Uppercase Greek alpha
Greek beta B Uppercase Greek beta
Greek gamma G Uppercase Greek gamma
Subfield codes Delete Retain

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Last update: Apr. 9, 2020