LC Control Number Structure  (010 Library of Congress Control Number - Structure)

The LC control numbering system has had the same basic structure since its initial use to control Library of Congress bibliographic information in card form beginning in 1898 (LCCN structure A).  On January 1, 2001, a structural change occurred (LCCN structure B).  The basic control number has been fixed in length at 12 characters and remains that length, although under LCCN structure A suffixes were occasionally used and under LCCN structure B the location of element parts is slightly altered to accommodate a four digit year.

Note:  Under both structures, the alphabetic prefix, year, and serial number are the basic elements required to make an LCCN unique.

Alphabetic prefix:  (3 digits before January 1, 2001; 2 digits after)

Prefixes are carried in a MARC record as lowercase alphabetic characters and serve to differentiate between different series of LC control numbers.  Prefixes are left justified and unused positions contain blanks (#).  If no prefix is present, the prefix portion contains blanks.

See:  Examples

Prior to the existence of MARC records, prefixes of various lengths were used on printed cards with combinations of uppercase or lowercase letters and numbers.  For MARC records, equivalents have been defined by the Library of Congress for some of these early prefixes, including those that were longer than two or three characters.  All other prefixes are input as found but in lowercase.

See Alphabetic Prefixes A to Z for a list of prefixes found on printed cards not printed from machine-readable records and how they are to be input into a MARC version of the record.  The list also includes some MARC prefixes not found only on MARC records.  Only prefixes which have a MARC form noted in the list should be recorded in machine-readable records.  (The alphabetic prefix for the Library of Congress control number is an authoritative-agency data element, maintained by the Library of Congress.)

Since the prefixes were used in records before 2001, they are found in the LCCN Structure A only.

Year:  (2 digits before January 1, 2001; 4 digits after)

For control numbers assigned under LCCN structure A, the year portion consists of two digits normally representing the year the record was created.  For control numbers assigned under LCCN structure B beginning with the year 2001, the year portion consists of four digits.

In most numbers, the year portion reflects the year in which the LC control number was assigned to the record for the bibliographic item.  During the 1969-1972 period, a 7-series year number was assigned.  In these numbers the initial digit of 7 was followed by a modulus-II check digit.  The year in which the card number was assigned can be approximated from the year portion of the Date entered on file (field 008/00-05).  With the reinstitution of the year series number in 1972, provisions were made to skip those individual card numbers which could have been assigned previously as a 7-series number.

Note:  7-series numbers were not used for non-book map material.  The prefix gm was used from 1968 through 1972.

For LC control numbers with two-digit years, the century may be determined according to the following table:

Serial number:  (6 digits before January 1, 2001; 6 digits after)

The serial number portion consists of one to six digits.  Serial numbers of less than six digits are right justified and unused positions contain zeros (0).  The hyphen which separates the year and the serial number on LC printed products is not carried in the MARC record.  For example, the number 85-2 is carried as 85000002 in a record.

Supplement number:  (LCCN structure A only)

This character position was originally defined to carry a supplement number for dashed-on supplement entries in bibliographic records.  Use of the supplement number was not implemented, therefore this position contains a blank (#).  Supplements and similar materials are now cataloged separately by LC and are carried as separate records with their own LC control number.  In some older records, information about supplements and similar materials is given in a 500 note field.

Suffix/Alphabetic identifier:  (LCCN structure A only)

Older LC control numbers sometimes include suffixes or alphabetic identifiers carried as variable length data following the Supplement number.  A single slash ( / ) introduces the suffix/alphabetic identifier.  Multiple occurrences of either suffixes or alphabetic identifiers are separated one from the other by a slash.  Suffixes and alphabetic identifiers do not affect the uniqueness of the control number.

All suffixes and alphabetic identifiers, except the revision date, appear in the MARC record as uppercase alphabetic characters.

On printed card copy, suffixes appear after the LC control number separated by a slash.  Suffixes have not been assigned since 1969 and they will be deleted from Library of Congress files in 1999.

Alphabetic identifiers appear on printed card copy as uppercase alphabetic characters beneath the LC card number in the lower right hand corner of the card.  Alphabetic identifiers were first assigned in 1969 and were used as distribution information for card copy by LC.  Alphabetic identifiers will be deleted from Library of Congress files in 1999.

See:  Examples

See:  Suffix/Alphabetic identifiers for the table of suffixes and alphabetic identifiers, including their explanations.

Revision date:  (LCCN structure A only)

The revision date associated with LC control numbers specified the latest date that the bibliographic data in a record underwent a change.  Revision data do not affect the uniqueness of the control number.  To account for the number of times significant changes have been made to a record beyond the first such change, a number was added as the last character of the revision date.  The date a record was originally created is the Date entered on file (field 008/00-05).

A revision date such as "r73" means that the record was changed in 1973.  The revision date "r743" means that significant changes have been made to the record three times, the last being made in 1974.

See:  Examples

The revision date was used as an indication of the degree of importance of a change made to a record.  A significant change to a record at the Library of Congress was defined as one important enough to warrant, among other things, redistribution of cards to LC's own catalogs.  A significant change included changes to:

content designation

an access point [fields 020 $a or $z, 028 $a, 050, 051, 082, 1XX, 240, 245 $a, 4XX (excluding 490), 6XX, 7XX, 8XX]

the extent of an item (field 300 $a)

the publication date (field 260 $c)

the record control number (field 001)

Leader/18 (Descriptive cataloging form).

Revision information was separated from a suffix or an alphabetic identifier by one slash ( / ).  If no suffixes or alphabetic identifiers are present, revision information was separated from the Supplement number by two slashes ( // ).  The inclusion of revision data was discontinued in 1999 and will be deleted from all records in the Library of Congress files.

To return, select:

010  Library of Congress Control Number