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- OIDs for each element type inside a MetaDataVersion (e.g., FormDefItemGroupDef) 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., a FormDef 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.ArchiveLayout OIDs must be unique within a single FormDef. ArchiveLayout OIDs may be reused in different FormDefs.
- Study OIDs must be unique within the containing ODM.Measurement Unit OIDs must be unique within the containing Study.
- 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.
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