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MARC DISCUSSION PAPER NO. 2025-DP09

DATE: May 22, 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); ISO 8601 (AD, BD, HD); Conversion date and time information (AD, BD, HD)

RELATED:

STATUS/COMMENTS:
05/22/25 – Made available to the MARC community for discussion.

06/25/25 – Results of MARC Advisory Committee discussion: The paper was generally supported by MAC, however there were suggestions for editorial refinements such as: 1) removing the phrase "strongly encouraged" from the proposed definition and using "preferred" instead; 2) removing the statement "Time cannot be recorded without a date" since it is in the ISO 8601 standard; 3) adding time zone so that it is more clear where in the world it is at that time; 4) explicitly recommending the use of the extended ISO 8601 because the simple version is outdated and can cause problems. A motion was approved to convert the paper into a Fast-Track proposal, incorporating the editorial suggestions. The paper was referred to the MARC Steering Group for final processing and approval as a Fast-Track proposal.

Discussion Paper No. 2025-DP09: 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 (yyyymmmdd). ISO 8601 supports appending the time in the form hhmmss.f to the date: yyyymmddhhiiss.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:ii: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.

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
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.  Only a date is required, but including the time is strongly encouraged.  Time cannot be recorded without a date.  Basic ISO 8601 date/time representation, which takes the form yyyymmddhhiiss.f, is permitted, but the ISO 8601 Extended Format, which uses separators to reduce ambiguity with a date/time instead taking the form yyyy-mm-ddThh:ii:ss.f (the decimal point and following digits are optional), is also strongly encouraged.

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$qDLC$u https://github.com/lcnetdev/bibframe2marc/releases/tag/v2.9.0

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

4.3.

884 ## $aDLC bibframe2marc v2.10-dev$g2025-03-03T08:16:47.0$qDLC$u https://github.com/lcnetdev/bibframe2marc/releases/tag/v2.9.0

[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]

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. QUESTIONS FOR DISCUSSION

6.1. Do you agree that the definition of subfield $g in Field 884 of the MARC 21 Formats should be expanded to include Time information as well as Date information?

6.2. Does the proposed revised definition of subfield $g adequately address this issue?

6.3 Has the flexibility built into ISO 8601 of displaying Date and Time in different formats been addressed sufficiently? 

6.4. Are there any other issues that should be addressed in this discussion paper?

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