[Data-modeling] Historical currency

[Christopher R. Maden]

Ed Laurent wrote:
> How about adding the Time span properties of Start and End date so that 
> any currency can be tagged with it's historical period? Ideally this 
> date feature would be linked to country. For example, several countries 
> use the US$ but over different time spans than the US. The other 
> currency properties of exchange rate, currency code, etc. are all the same.

I thought of this, and it would work, but it seems unnecessarily 
complicated for now.  We are still thinking about generalized 
time-valued properties, but it seems useful to make the simple 
distinction between currencies in use and currencies formerly in use. 
Wikipedia can do this easily because links are all one-way; the Zambian 
pound links to Zambia, but Zambia makes no mention of the pound.  We 
picked up that one-way assertion and made it reciprocal, which gives the 
misleading impression that Zambia currently uses the pound; we should be 
able to capture the distinction without overcomplicating the model — or 
indeed without knowing the dates involved.  This last point is a problem 
with time-valued properties; if I know that something was true in the 
past but I don’t know *when* it stopped being true, I can either lie 
(excuse me, “guess” — er, “estimate”) or make an assertion that appears 
to be currently true; neither is ideal.

~Chris
-- 
Christopher R. Maden
Data Architect
Metaweb Technologies, Inc.
<URL: http://www.metaweb.com/ >