Define range information

[fengbozheng]

Hi everyone,

I'm currently trying to build an ontology myself and I want to define several Classes like "Has_Sympton1_MoreThan1Year" and "Has_Sympton1_MoreThan2Years." And I want "Has_Sympton1_MoreThan2Years" to be a subtype of "Has_Sympton1_MoreThan1Year." What is the most common way to model such Classes (or model the information of time range)?

Thanks,
Fengbo