[uf-new] Currency brainstorming

[Guillaume Lebleu]

Frances Berriman wrote:
> Interesting.  Would date/time sensitive money in the case of stocks
> and shares apply in this way too, do you think? Or would that be
> reliant on publish date of where the information is displayed? (Not
> that I know much about S&S, just occurred to me it's a much more
> common varying value)
>   
IMO, we must conceptually distinguish the notion of *money amount* and 
the notion of *price*. A money amount is an amount of a given number of 
units of currency. A price is an equivalence relationship typically 
between a money amount and another amount in any measurement unit. Some 
prices are expressed without using currencies. Some prices are prices of 
one currency in another one (as in 1 euro = 1.41 dollars).

The amount+unit is not a relation and does not change over time, and 
does not have to be dated.

A price does change over time, and should be dated.

In Andy's example above, the date is not a property of the "hmoney" 
class, but of a TBD "hprice" class.

Guillaume