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The EV parameter may take 3 values, defined as follows. It is a required field in the metadata template.
| Parameter value | Definition |
|---|---|
| I | The template referred to by this metadata template was inserted into the RTS by the entity designated by iuid |
| X | The template referred to by this metadata template was invalidated by the entity designated by iuid |
| R | The template referred to by this metadata template was re-validated by the entity designated by iuid |
A template may be invalidated in revalidated and subsequently invalidated again and etc. any number of times through the history of the RTS. There will be a new metadata template for each insertion, invalidation, and revalidation.
The original metadata template specification did not envision the possibility that assertions that templates are in error might themselves be made in error. And thus there was no mechanism to restore templates mistakenly asserted to be in error.
One disadvantage to this approach is that to query "good" data in the RTS, the query must check disjunctively for the values I and R. Alternatively, we could add a flag to the templates themselves that determines whether they are valid. This flag would be set to true upon insertion and revalidation, and to false upon invalidation.
The EC parameter
The EC parameter takes the same values as the original E parameter except for the value I (insertion). It is not a required field in the case of a template insertion or revalidation.