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Constraints

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.

 

EVENT_CONSTRAINTS=

 

<Constraints>

<Constraint { AfterEvent=’key’  |  BeforeEvent=’key’  

 | FromEvent=’key’   |  UntilEvent=’key’

 | AtEvent=’key’ } >

[ NARRATIVE_TEXT ] ...

</Constraint> …

</Constraints>

 

The interpretations of the elements are as follows:

 

  • AfterEvent. Current event > specified event
  • BeforeEvent. Current event < specified event
  • FromEvent. Current event >= specified event
  • UntilEvent. Current event <= specified event
  • AtEvent. Current event = specified event

 

If there are causal relationships between Events then the narrative 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.

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