Being able to place limits on Events that relate to other Events is a powerful feature. The <Constraints> element allows an Event to be sequenced relative to one-or-more other Events.
<Constraints>
<Constraint { AfterEvent=’key’ | BeforeEvent=’key’
| FromEvent=’key’ | UntilEvent=’key’
| AtEvent=’key’ } >
[ TEXT_SEG ] ...
</Constraint> ...
</Constraints>
The interpretations of the elements are as follows:
If there are causal relationships between Events then the <Text> elements can be used to describe it.
The context of the Constraint, i.e. whether it appears in a <When> or <Until> element, determines whether it relates to the start or end date. If the specified Event is a simple Event then its only date is always applicable. Only one constraint for a given context may be established between two particular Events (e.g. no duplication for a start date), and they must not be self-referential.
Q: Should the relationship between events involve an optional duration? For instance: event-B is after event-A + 3 months. GenTech V1.1 (appending C3) suggested something similar: “Date data can be relative. Dates can be relative to an event, such as “four months after marriage”.
Q: Do we need multi-unit durations, such as 3y 120d? This would affect the ‘Age’ Property of both Person and Animal.