The elements in the data portion of an ODM file that apply to a single entity must occur in temporal order. That is, the transactions on each entity are applied in the order in which that entity's elements occur in the file, and Signatures and AuditRecords must occur in increasing value of their DateTimeStamps.
In general, the elements for distinct entities do not have to be ordered relative to one another. However, when an entity is signed, all transactions on that entity that occurred before the time of the signature must be present earlier in the same ODM file or in a prior ODM file in a linked series.
All the DateTimeStamps in a file must precede the CreationDateTime of that file.
In a linked series of ODM files, the AsOfDateTimes of those files must occur in temporal order, and the DateTimeStamps in each file must be later than the AsOfDateTimes of the prior file.
The ordering for data elements can be asserted with the use of RepeatKey (e.g., StudyEventRepeatKey, ItemGroupRepeatKey) attributes. Note that this is relative to the parent element, and is expected to follow Upsert semantics (see Section 2.10, Transactions); the series of RepeatKey values are expected to be contiguous.
A data entity (like an item group) can be represented as a series of data elements. These elements can contain data for disjoint parts of the entity (properties and children), sequential changes to the same parts, or a mixture of the two.
In a study, the initial or default value of any clinical data is assumed to be "NULL". Thus it is not necessary to include null valued items in a Snapshot transfer. Neither is it necessary to include a null value as the first in a series of insertions and updates of an item.
Systems that generate ODM files should attempt to minimize the number of elements in such files. Thus, if 2 elements for the same entity can be merged without changing the semantics of the events described (and without violating any of the ordering rules), the merged version is recommended. Similarly, unnecessary elements should be omitted.