The MODS Editorial Committee has considered the proposal to add a 
relatedItem type value for expressing the relationship between a 
research publication and the data set(s) that it is based on. A 
comparable element describing this relationship is included in MARC 21, 
786 (Data Source Entry). However, it was also pointed out on the 
listserv that only including a relatedItem type for datasets may be too 
narrow to address the larger issue of different types of accompanying 
materials deposited in repositories and that an approach allowing for 
the inclusion of external vocabularies may be preferable.
The entire listserv discussion can be found here:

The  MODS Editorial Committee feels that new type values for relatedItem 
should be added only when they are strongly justified. Instead, we would 
like to introduce a mechanism whereby type values from external 
vocabularies can be supplied.   We propose the addition of 4 new 

  * otherType
  * otherTypeAuth
  * otherTypeAuthURI
  * otherTypeURI

@otherType may be supplied alone, in which case it is an uncontrolled type.
If @otherType is supplied along with @otherTypeAuth, then it is a 
controlled type where @otherTypeAuth is its authority.
@otherTypeAuthURI may be used to supply a URI uniquely identifying the 
vocabulary from which the controlled type has been selected.
@otherTypeURI may be used to supply a URI uniquely identifying the 
controlled type value from a vocabulary.

The MODS Editorial Committee solicits comments on this proposal. We'd 
like to receive feedback by August 15.

Melanie Wacker
on behalf of the MODS EC