Combat Zone Periods is the only plural data class for a worker but the data elements are potentially plural (End date(s) and Start date(s)). These suggest that a single work would only have one instance the data class with potentially multiple start and end dates. But the cardinality of the data class relative to the Worker is 0..*. Please clarify if the data class can repeat for a work and how many times a data element can be present in an instance of the data class