[Data-modeling] Historical currency

[Jeff Prucher]

> -----Original Message-----
> From: data-modeling-bounces at freebase.com 
> [mailto:data-modeling-bounces at freebase.com] On Behalf Of Jeff Thompson
> Sent: Monday, March 31, 2008 11:59 PM
> To: Freebase data modeling mailing list
> Subject: Re: [Data-modeling] Historical currency
> 
> Christopher R. Maden wrote:
> > 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.
> 
> The problem assumes a property can only be true over one 
> continuous time span.  But think of a country occupied by the 
> Romans, then beaten back, then occupied again, then finally 
> defeated.  What is time-value for the property that says the 
> country has Roman currency?  Time-valued properties need to 
> allow for multiple periods.  So in your case above, if you 
> know that something was true in the past, even for a day, 
> then assert that period.  If someone else can show that it 
> was true for some period after that, then that period of 
> validity can be added too.

I don't think Chris was suggesting that a time-valued currency property
would be unique. The problem is not with representing values that change
over time, even if they change back and forth; that's very simple and
implicit in most time-valued properties I can think of (Grover Cleveland's
two non-contiguous terms as U.S. President are an example of this that I
know is in the graph). The problem is making assertions about data for which
we have no time-value information but which is modeled as being time-valued.
So it's one thing to say a country had Roman currency from M to N, then its
own currency from O to P, then Roman again from Q to R, and then its own
currency starting again at S. This is good, clear data. It's another thing
entirely to say that a country has or had Roman currency and its own
currency; without dates, you have no way of knowing which (if any) is the
current currency and which are historical. Since this is the quality of data
that we currently have (i.e., I think Chris is trying to avoid this issue by
making the properties binary. So we can assert that certain currencies are
current, and that certain currencies have been used at a time or times in
the past but are no longer used.



Jeff Prucher