Schema Endorsement: how and why
The external schema endorsement process
The endorsement process for an external schema may be initiated
either by the METS Board, or by the community that develops
and/or wishes to use the particular schema. Users should not
assume that schemas not appearing the list of endorsed schemas
are not suitable for use in METS. The METS Board may simply
not have reviewed such schemas yet. Requests for such a review
should be submitted to the METS
The purpose of external schema endorsement
METS does not specify an XML vocabulary and syntax for descriptive
and administrative metadata. The METS dmdSec, techMD, sourceMD,
digiprovMD and rightsMD elements can reference external metadata
in any digital format, or contain such metadata either in base64
encoded format or in XML format. XML encoded metadata used in
these METS contexts can either conform to an external schema
or to no schema.
To encourage the use of community recognized standards, the
METS Editorial Board endorses schemas that it feels are especially
suitable for use in governing XML metadata appearing in or referenced
from the METS dmdSec, techMD, sourceMD, digiprovMD and rightsMD
elements. Such endorsement indicates:
- 1. The endorsed schema represents the consensus of a community
- 2. The schema has achieved production status.
- 3. The schema is maintained for use by an organization representing
the community that developed the schema; and is made publicly
available by this organization from an official, web-accessible
- 4. The METS Board has reviewed the schema and satisfied itself
that it can function effectively in a METS context.
The relationship of the MDTYPE attribute to endorsed external
The METS schema includes an MDTYPE attribute on its mdRef and
mdWrap elements that is governed by a controlled vocabulary
list (or "enumeration" in XML schema terms). While
the types of metadata that are represented by endorsed schemas
should all be represented in the MDTYPE controlled vocabulary
list, the list may also include metadata types represented by
schemas that have not been endorsed and metadata types that
are not represented by schemas at all. The controlled vocabulary
list is simply intended to reflect commonly used metadata types,
and to facilitate the sharing of METS files among institutions.
The MDTYPE value list is not closed, and METS users may submit
requests for additions to the list on the "METS
Schema Revisions Requests" page of the METS wiki. METS
users can also record types of metadata not represented in the
MDTYPE controlled vocabulary list by specifying "OTHER"
as the MDTYPE value and then recording the specific type of
metadata in the uncontrolled OTHERMDTYPE attribute.
The METS Board is currently considering options for managing
its controlled vocabularies outside the METS schema itself.
It is difficult to anticipate the metadata types that METS users
may want to record in the MDTYPE attribute, and thus keep the
associated controlled vocabulary lists current. The METS Board
is seeking the best way to keep its controlled vocabularies
current and useful while still encouraging consistency in the
their use. Suggestions and comments may be directed to the METS