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The metadata for a study is defined in a series of MetaDataVersion elements. Through this mechanism (multiple MetaDataVersion elements), the model supports the incremental deployment of "mid-stream study changes," and thus can handle a situation where multiple versions of the metadata are being used simultaneously (e.g., due to delays in IRB approval at various sites).

The way metadata versioning works is as follows. An individual Study element may contain multiple MetaDataVersions, reflecting 1 or more mid-stream study design changes. The initial version contains a full set of metadata. Each subsequent version typically contains only modified or newly added metadata elements, inheriting the previous metadata by an explicit reference. The same metadata elements in different versions will have the same OID. This approach is used to allow the older versions of the metadata to remain intact, while simultaneously providing a concise way to represent changes.

A metadata version defines the types of study structural elements, workflows, event timings, study event groups, study events, item groups, and items that form the study data.