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MARC PROPOSAL NO. 2025-FT02

MARC FAST-TRACK PROPOSAL

DATE: August 28, 2025
REVISED:

NAME: Redefining Subfield $g to Accommodate Time as well as Date in Field 884 of the MARC 21 Formats

SOURCE: Library of Congress, Policy, Training, and Cooperative Programs Division (PTCP)

SUMMARY: This paper discusses expanding the scope of subfield $g (Conversion date) in field 884 (Description Conversion Information) of the MARC 21 Bibliographic, Authority, and Holdings Formats to include Time information in addition to Date information.

KEYWORDS: Field 884 (AD, BD, HD); Description Conversion Information (AD, BD, HD); Subfield $g, in field 884 (AD, BD, HD); Conversion date (AD, BD, HD); Conversion date/time (AD, BD, HD); ISO 8601 (AD, BD, HD); Conversion date and time information (AD, BD, HD)

RELATED: 2025-DP09

STATUS/COMMENTS:
06/25/25 – Discussion Paper 2025-DP09 was converted to a MARC Fast-Track proposal at MAC Annual meeting.

08/28/25 – Submitted to the MARC Steering Group for consideration as a MARC Fast-Track proposal.

09/04/25 – Results of MARC Steering Group review - Approved.

Proposal No. 2025-FT02: Redefining Subfield $g to Accommodate Time as well as Date in Field 884

1. BACKGROUND

Subfield $g in the 884 field (Description Conversion Information) in the MARC 21 Formats is currently defined as follows:

$g - Conversion date
Date on which the data was converted. Date is recorded in the format yyyymmdd in accordance with ISO 8601, Representation of Dates and Times.

Many conversion specifications, including the Library of Congress's BIBFRAME-to-MARC conversion specification, include Time information as specified in ISO 8601, in addition to Date information.

2. DISCUSSION

ISO 8601, Representation of Dates and Times, includes Time information as well as Date information. The current definition of subfield $g in the 884 field in the MARC 21 Formats limits the use of ISO 8601 to only the date component.

Field 884 was defined to record information about a machine conversion of the record as a whole.  While a date seemed sufficient in 2015, when the 884 was created, in practice it has proven insufficiently inexact. A record may go through multiple conversions in a single day and, with only a date permitted, it is impossible to know when each of those conversions occurred. Since conversion events typically occur at a precise moment in time and since the work is being carried out by programming, it is not only easy to know precisely when the event happens (down to the second), but also equally trivial to include the time of the event. Agencies using the 884 field wish to also include Time information (in accordance with ISO 8601) in the subfield $g. The present definition of subfield $g also prescribes an exact way to enter the date (yyyymmdd). ISO 8601 supports appending the time in the form hhmmss.f to the date: yyyymmddhhmmss.f.  This matches how an ISO 8601 date/time is used in subfield $c of field 583 (Action Note).  Most systems – machines, programming languages, and also a standard like EDTF – today use the ISO 8601 Extended Format for date/time information, which uses separators to eliminate ambiguity: yyyy-mm-ddThh:mm:ss.f. "T" is used between the date and time components; hyphens between the date components; and colons between the hour, minute, and second components; a period before any sub-second information.

The basic instruction to use a date/time formatted according to ISO 8601 will remain in the documentation about the use of $g in 884, which will ensure any existing data are backwards compatible with this change, but the subfield documentation will urge the use of ISO 8601 Extended Format.

This paper stems from Discussion Paper No. 2025-DP09, which was generally supported by the MARC Advisory Committee at the 2025 Annual meeting. A motion was approved to convert the paper into a fast-track proposal with the amendment to make editorial changes to the proposed definition of subfield $g.

3. PROPOSED CHANGES

In fields 884 (Description Conversion Information) of the MARC 21 Bibliographic Format, MARC 21 Authority Format, and MARC 21 Holdings Format, rename and redefine subfield $g as follows (added text in bold and underlined):

$g - Conversion date/time (NR)
Date/time on which the data was converted. Date/time information is recorded in the format yyyymmdd in accordance with ISO 8601, Representation of Dates and Times. When this subfield is used, the date is mandatory. Time may also be included. ISO 8601 Extended format is preferred since the Basic format with minimal separators is not always parsable and the delimiter-less format was removed from the ISO 8601 standard in 2019 and is no longer considered compliant.

4. EXAMPLES

4.1.

884 ## $aStanford Bibframe to MARC transformation, version 1$g2014-10-02$kstfbf1039806$qCSt$uhttp://stanford.example.com/Bibframe2MARC_v1.xsl

[BIBFRAME to MARC Conversion with Date only, ISO 8601, Extended format]

4.2.

884 ## $aDLC bibframe2marc v2.9.0$g2025-03-03T08:16:47.000$qDLC$uhttps://github.com/lcnetdev/bibframe2marc/releases/tag/v2.9.0

[BIBFRAME to MARC Conversion with Date and Time, ISO 8601, Extended format]

4.3.

884 ## $aDLC bibframe2marc v2.10-dev (libxslt)$g2025-03-03T08:16:47.0$qDLC$uhttps://github.com/lcnetdev/bibframe2marc/releases/tag/v2.10.0

[BIBFRAME to MARC Conversion with Date and Time, ISO 8601, Extended format, fractional seconds reduced to one value in the Time representation, a reduction that is permitted by the standard.]

4.4.

884 ## $a DLC bibframe2marc v2.10-dev (libxslt)$g2025-06-24T10:30:00-04:00$qDLC$uhttps://github.com/lcnetdev/bibframe2marc/releases/tag/v2.10.0

[BIBFRAME to MARC Conversion with Date and Time, ISO 8601, Extended format, showing UTC offset for Eastern Daylight Time, United States (UTC -04:00)]

5. BIBFRAME DISCUSSION

The Library of Congress MARC-to-BIBFRAME conversion follows ISO 8601, Extended format for both Date and Time. Extended format includes the use of hyphens between YYYY, MM, and DD in the Date values, the letter T to separate Date and Time values, colons between MM and SS in the Time values, and a decimal to separate MM and SS from MsMsMs in the Time values.

6. SUMMARY OF PROPOSED CHANGES

In fields 884 (Description Conversion Information) of the MARC 21 Bibliographic Format, MARC 21 Authority Format, and MARC 21 Holdings Format, rename and redefine subfield $g (Conversion date) as follows (see Section 3 for specific edits):

$g - Conversion date/time (NR)
Date/time on which the data was converted. Date/time information is recorded in accordance with ISO 8601, Representation of Dates and Times.  When this subfield is used, the date is mandatory. Time may also be included. ISO 8601 Extended format is preferred since the Basic format with minimal separators is not always parsable and the delimiter-less format was removed from the ISO 8601 standard in 2019 and is no longer considered compliant.

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