Inconsequent definition of Reference Period

[PerWiklander]

Population has this attribute:

Name	Description	Cardinality	Value Type
Reference Period	The time period to which the population is associated.	0..1	Date

Statistical Programme Cycle has two attributes:

Name	Description	Cardinality	Value Type
Reference Period Start	Start date of the reference period	1..1	Date
Reference Period End	End date of the reference period	1..1	Date

Either Population needs two attributes of type Date, like Statistical Programme Cycle, or they should both have a single attribute like:

Name	Description	Cardinality	Value Type
Reference Period	...	0..1	DateRange

where DateRange is defined as

Name	Description	Cardinality	Value Type
Start	Start date of the date range.	1..1	Date
End	(optional) end of the date range.	0..1	Date

[InKyungChoi]

If the attribute name is "Reference Period", I guess it has to have start-end date like Statistical Programme Cycle? What do you think? @JALinnerud, @FlavioRizzolo, @FrancineK

Additionally, if Population refines Universe by specifying geography and time, should these attributes mandatory? Would there be a Population we don't expect to have geographical boundary or time period..?

[JALinnerud]

I do think we can have a Population without either a geographical boundary or a time period