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The ItemGroupDataSeq doesn’t have any other meaning than the sequence in which the items are saved and exchanged for each ItemGroupDef. It is equivalent to the observation # in a dataset.
PROPOSED BUSINESS RULE (Jozef): ItemGroupDataSeq may only be used when ItemGroupData is a direct child of either ClinicalData or ReferenceData and the ItemGroupData represents a row in a dataset.
ItemGroupData can also occur as reference data. In that case, the ItemGroupOID and ItemGroupRepeatKey pair must be unique within the reference data.
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