Metadata Extensions and Profiles

Customizing metadata standards with extensions and profiles

The Common Standards guide describes widely used standards for projects seeking a generic metadata approach. These standards were generally created for broad application, and thus usually represent the lowest common set of metadata that applies to many disciplines. These standards provide an organized way to represent many of the general characteristics of a dataset.

However, a general standard cannot include every element or relationship that is important to every discipline within a broad subject area. To accommodate specialized needs, users can either select a more specific metadata standard (one developed for a specific kind of data or use), or a metadata extension or profile that is based on a more general standard.

Special metadata elements that contain discipline-specific information can be added in ways that comply with the rules of the more general standard. These additions are called extensions and result in the creation of a profile for a specific discipline to which the standard is then applied.

Metadata standards are typically managed in a way that supports the creation of specialized forms of the standard to meet the needs of a particular community. However, the changes must not make the standard less strict. Changes may not alter the particulars of the original standard but provide a definition for an extension or a profile of that standard.

To demonstrate an extension making a standard more strict, suppose a metadata standard has an optional metadata element named sensor_owner. It Because it is optional, a metadata creator may or may include it in project metadata. However, one particular organization that creates metadata using this standard, considers this information to be critical. Thus, the organization mandates that their metadata records will always contain the sensor_owner element. This mandated field is considered an extension to the original standard, and the specialized form of the standard created by the addition of the extension is called a profile. The organization has extended the metadata standard to meet their particular needs, while not contradicting any required content as specified by the standard.

Standards can be extended in other ways. Sometimes a metadata standard does not provide all the elements required by a community. In this case, the community can extend the standard by adding new elements.

For example, if a project were collecting shoreline data, wave height might be an important piece of information to convey. Wave height is relevant in a few specific environments but not for all environments, so a general standard might not include an element for wave height. One solution might be to include wave height in an existing free-text element within the more broadly-applicable standard. For example, wave height could be included within the Description element of FGDC's Content Standard for Geospatial Metadata or in the Summary element of the Directory Interchange Format. The problem with this approach is that unstructured information (that is, free text) can't be easily searched or categorized by a computer. So, if wave height is an important enough detail, a it can be added as an extension, as long as it complies with the rules of the standard.

In all cases it is important to keep in mind that community-based extensions must follow strict rules for extensions as set by the original standard.

Types of Extensions

A metadata extension is the sum of additions to a metadata standard that allow users to provide information in additional fields or in additional ways that were not specified in the original standard.

In standards such as ISO 19115, extensions include the following types of changes:

  • Addition of a new metadata section
  • Alteration of the domain of a metadata element (for example, assigning a code list to specify what responses are allowed for that metadata element)
  • Addition of terms in a code list
  • Addition of a new metadata element to an existing metadata element
  • Addition of a new metadata entity
  • Changing the obligation of a metadata element from optional to mandatory (but not the reverse, which would break the core standard)

Constraints are considered a specialized subset of extensions, in which additional restrictions are placed on the standard. In the above list the second and last items are constraints. In this case the term “extension” describes the addition of information to the standard, even though the metadata instances that follow the standard are thereby restricted. More succinctly, the standard is expanded, but the metadata is restricted.


A metadata profile is the community-specific application of a metadata standard. Profiles must meet the core requirements of the metadata content standard; that is, they must provide the mandatory elements that the standard requires. But they also include extensions (described above).

A metadata content standard is composed of the core metadata set and optional elements:

  metadata content standard = core metadata set + optional elements

Therefore, a profile also can be thought of as the sum of these component parts:

  profile = core metadata set + optional elements + extensions

Profiles are used to adopt a more general standard to a particular domain-specific purpose. One example is the Shoreline Profile for CSDGM. The CSDGM metadata standard is designed to document a wide variety of geospatial data. The Shoreline Profile was created to better tailor CSDGM to data that were taken from a shoreline location or from a location that intersects a shoreline. This profile includes the following changes: changing some elements that are particularly important for shoreline data from optional (in CSDGM) to mandatory; requiring that certain keywords be taken from an approved shoreline glossary instead of allowing free text; and adding new metadata elements, such as Time_of_Tide and Wave_Height, that can be relevant to shoreline data, but are not relevant to all geospatial data.

These examples of metadata profiles demonstrate how profiles relate to the original standard:

See the MMI Guide on Discipline-specific Profiles and Extensions for the Marine Community for more information on this topic.

Management of Extensions and Profiles

In most standards organizations, a formal metadata extension or profile must be approved by the organization that approved the original standard. This complex process can take some time, but it results in official approbation” that will reassure users about the validity of the extension or profile. Also, this process provides a way for the approving organization to publicize the standard, along with any extensions or profiles, in a single web site or reference.

Some groups might want to extend a standard to meet their particular needs without going through the lengthy review and approval process. This option is feasible, but there are disadvantages to this approach:

  • Communities won't be able to locate the extensions and profiles as readily
  • Profiles with additional elements can break software that doesn't know about those elements
  • Some metadata standards may have legal restrictions on their re-use in a non-approved profile or extension

Value of Extensions and Profiles

The developers of most content standards expect and encourage the development of extensions and profiles and may direct how they are to be specified or registered. A community that adopts a profile increases the interoperability of its metadata between groups within the community. Potentially, it even increases its interoperability with communities that use other profiles, because the use of the core metadata elements is shared. This view on interoperability is not shared by all members of the metadata community; some individuals feel that a proliferation of profiles and extensions reduces interoperability, since each group's metadata are not fully interoperable with metadata of other groups. These viewpoints must always be considered when deciding whether to confine metadata elements to those in the core standard, to lobby for changes to the core standard, or to customize your metadata with extensions and profiles.

Suggested Citation

Graybeal, J., Isenor, A., Neiswender, C., Stocks, K., Bermudez, L. 2011. "Metadata Extensions and Profiles." In The MMI Guides: Navigating the World of Marine Metadata. Accessed July 16, 2020.