source-id-type Source Identifier Type (in Related Object)

Type of source identifier (for example, a DOI, ISSN, ISBN, or publisher’s identifier) for a <related-object>.
OPTIONAL on element: <related-object>
Value Meaning
The type of identifier that names the source of the related object, for example, a DOI The type of document identifier named in the @source-id attribute for a (<related-object>) element. This attribute qualifies the @source-id attribute.
Restriction This is an optional attribute; there is no default.