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Top-level Element: <extension>

Element <extension>
Definition Provides additional information not covered by MODS.
Attributes displayLabel
Subelements None



<extension> may be used for elements that are local to the creator of the data. In addition, it may be used to extend MODS for various purposes when another XML schema may handle the type of information. Depending on the nature of the added information, <extension> may be a container element.

This element is repeatable.

Specific DLF/Aquifer Guidelines

The DLF/Aquifer Implementation Guidelines for Shareable MODS Records generally recommend against the use of the MODS <extension> element because any subelements within it will likely not be understandable to Open Archives Initiative (OAI) service providers. An exception to this recommendation is the use of well-documented community-based information for which there is not another appropriate place within the MODS schema. An example of this is the use of the "asset action" package.

Metadata falling within the scope of <extension> in a local environment should be included within other MODS elements as appropriate or omitted in OAI-harvestable MODS records.

See the <extension> entry in the DLF/Aquifer Guidelines Summary of Requirements and Recommendations table for further information on requirements of this element, its attributes, and subelements.

Aggregator information: As noted above, aggregators are not likely to include or use the <extension> element unless it is used to contain an agreed-upon set of information in a recognizable schema.

The <extension> element is not discussed in the DLF/NSDL Best Practices for Shareable Metadata External Link. However, the section on "Appropriate Representation of Resources" contains some information on what types of information to provide within metadata that is being shared via OAI (or by other means).

Element Description



See the Attributes used throughout the schema for descriptions of each.


There are no subelements for <extension>.



Uses extension element to include degree information, which is not in MODS:

<extension xmlns:etd="">
<etd:name>Doctor of Philosophy</etd:name>
<etd:discipline>Educational Administration</etd:discipline>
[Alternatively, the XML definition may be at the top of the document.]
<url access="asset action package"> </url>



MARC Mapping (Bibliographic)

There is no direct mapping, but this element could include MARC 21 9XX fields or field 887 (Non-MARC Information Field).

Dublin Core Mapping

The <extension> element itself is not mapped to Dublin Core in the MODS to Dublin Core Metadata Element Set Mapping Version 3.0 (June 7, 2005), however Dublin Core elements may be used within <extension>.

Use of the <extension> element to include a Dublin Core element for when a date resource was modified:

<extension xmlns:dcterms="">

[Alternatively, the XML definition may be at the top of the document.]


Last Updated: August 2, 2018