NACO normalization is a set of rules for eliminating small differences from character strings. Normalization is good, but NACO normalization isn't good in all cases. For more information, please click "Continue reading."
Normalization is the practice of simplifying character strings for comparison and sorting. Typically normalization removes case differences from letters by making them all capitals or all small letters; removes punctuation that might vary accidentally between two headings for the same thing, or might complicate sorting; changes combined characters and characters marked by diacritics into a simpler, unmarked forms; etc.
NACO normalization is primarily a set of rules for normalizing MARC encoded name and title headings. This means that NACO normalization goes beyond the rules listed above to include some more specialized rules needed for its particular task. For example, the first comma in a personal name heading usually marks a distinction between surname and forename, and NACO normalization retains it. A name heading in inverted form with a comma and in direct order form without a comma are not considered to be the same, e.g., "Chandra, Prakash" and "Chandra PrakÄ?sh" are both valid NACO headings, and the first comma rule allows them to be distinguished after normalization.
MARC headings are divided into subfields. In name headings, there are cases where the same data element can be found coded with different subfield values, one current and the other obsolete. NACO normalization deals with this by removing the subfield value, but leaving the subfield position marked; i.e., $a $b and $c get normalized to $-, $-, and $-. This means that insignificant or erroneous differences in subfield code values do not affect comparison and sorting, so "$a Microbiology Conference $b (1st ...)" and "$a Microbiology Conference $n (1st ...)" can index the same; likewise "$a Smith, John, $d 1953- " and "$a Smith, John, $c 1953- "
However, outside of MARC name and title headings, the NACO normalization rules do not necessarily lead to good results. Subject headings sometimes use the same words to mean different things, with the difference signified by the subfield code used. For example, under current coding practice, "... $x Portraits" and "... $v Portraits" mean different things when they appear in a subject heading string (the former is a work about portraits of a person, while the other is a collection of those portraits). Treating them as identical is not necessarily the best choice--though neither is indexing them separately with no indication of what the difference between them is, but that's a different discussion. Similarly, the first comma in a topical subject string does not mark a valid distinction between to headings; e.g., "Short stories, African" and "Short stories African" would not both be valid, separate headings, and allowing normalization to treat them as identical prevents an inadvertantly omitted comma from disrupting filing order.
There are also kinds of normalization which NACO normalization does not include, but which have proven very useful. NACO normalization makes no changes to numbers, but there are standardized changes that can be made to numbers in specified subfields that will enable them to file in a numeric rather than a decimal order (i.e., 3, 21, 111 instead of 111, 21, 3). This type of normalization may be judged appropriate, despite not being part of NACO normalization.
More details about NACO normalization can be found at http://www.loc.gov/catdir/pcc/naco/normrule.html .