...
- OIDs for each element type inside a MetaDataVersion (e.g., ItemGroupDef) must be unique within the scope of that MetaDataVersion.
- It is best practice to make OIDs unique within the entire MetaDataVersion, however it is allowable to use the same OID for different element types if necessary, e.g., an ItemDef may have the same OID as an ItemGroupDef. This is not recommended.
- Elements in a MetaDataVersion may have the same OID as ones in an Included MetaDataVersion. An element in a MetaDataVersion with the same OID as the same element type in an Included MetaDataVersion is interpreted as replacing the earlier definition. See 3.1.1.3.1 Include.
- MetaDataVersion OIDs must be unique within the containing Study.
- Study OIDs must be unique within the containing ODM.
- User, Location and Signature OIDs must be unique within the containing AdminData.
- Whenever an element uses an OID to reference another element, the referenced element must occur within the same document as the reference or within a prior document in a linked series. Thus, the referenced element can always be found by tracing back through the PriorFileOID links.
...