Date interval with unknown dates

I am working on a site which will contain information about locomotives & railroads. It needs to show the service period o fa locomotive at a railroad, as a date interval.


Service Period: January 1954 - November 1958

I am using Interval Data of the Numeric Data Types module for this field. As the data is not complete, there can still be quite a few unknowns.

Service Period: 1954 - November 1958
Service Period: 1954 - 1958
Service Period: ? - November 1958
Service Period: ? - ?

The first 2 examples above are not an issue. The last 2 however I can not get work with the mentioned module. How best to do this?

The NumericDataTypes module is based on the ISO 8601 standard, which does not support uncertain, approximate, or unbounded qualifiers. Because of this, the module requires a minimum amount of precision to work correctly. There is an extension to the standard (EDTF) does include those qualifiers, but it’s unlikely that they could be integrated in NumericDataTypes, given the way it’s implemented.

One way to simulate uncertain dates is to replace a β€œ?” with a date that’s far in the past or future. So, β€œ? - November 1958” could be β€œ-9999 - November 1958” and β€œ? - ?” could be β€œ-9999 - 9999”.

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