No subject
Sun Mar 31 09:34:23 UTC 2013
around the world in recent years (at least since 1944 - before that it
was the British pound), The Yen came in at some point but lost its
traction around the Japanese recession. There are now more Euros in the
world than Dollars so people have been discussing using the Euro as
reference currency.
I have no idea what would be best and I have no idea how this is usually
done in practice. I feel this is just something we need to decide and
I'd like your input on this.
5. Where do we get the exchange rates from?
There are a few ways to get the exchange rates. One is to use
http://openexchangerates.org (they have a simple json based api, 164
currencies, and historical rates reaching back to 1999). However they
charge for their api requests. We could scrape it ourselves from
websites and put up a conversion service ourselves. There might be other
sources I don't know about. Any suggestions?
There are probably more questions that need answers, but let's start
with these. All input is greatly appreciated.
--
Tryggvi Björgvinsson
Technical Lead, OpenSpending
The Open Knowledge Foundation <http://okfn.org>
/Empowering through Open Knowledge/
http://okfn.org/ | @okfn <http://twitter.com/OKFN> | OKF on Facebook
<https://facebook.com/OKFNetwork> | Blog <http://blog.okfn.org/> |
Newsletter <http://okfn.org/about/newsletter>
--------------040806070800010107010103
Content-Type: text/html; charset=ISO-8859-1
Content-Transfer-Encoding: 7bit
<html>
<head>
<meta http-equiv="content-type" content="text/html; charset=ISO-8859-1">
</head>
<body text="#000000" bgcolor="#FFFFFF">
Hi,<br>
<br>
I'm looking at issues 252[1] and 282[2] on github. They've been
there for 2 years but I think implementing them is extremely
important for openspending. Currently we look at currencies at their
face value (as if the currencies have a fixed value). This means
that all historical comparisons are inaccurate since the value of
the currencies differs (and now after an world-wide economic crash
the error might be huge).<br>
<br>
[1]: <a class="moz-txt-link-freetext" href="https://github.com/openspending/openspending/issues/252">https://github.com/openspending/openspending/issues/252</a><br>
[2]: <a class="moz-txt-link-freetext" href="https://github.com/openspending/openspending/issues/284">https://github.com/openspending/openspending/issues/284</a><br>
<br>
In my opinion we should always compute the value of the currency
when presenting it (and allow users to choose which currency they
wanted presented in). This will make historical and international
comparisons more accurate (I say more because we cannot always get
the exact value of the currency, e.g. when date for transaction
isn't accurate).<br>
<br>
So what I want to do is always store the amount measurement in the
same currency (across all datasets), automatically add an attribute
for the default currency (the one we exchange it from) and then when
presenting the amount we present it at the current value. This setup
can have some implications though (more on that below).<br>
<br>
This raises some questions I wanted to ask here on the list.<br>
<br>
1. How would the schema/dimensions look like?<br>
<br>
I say we keep amount as measurement but store a converted value in
it and add an attribute declaring the default currency. This
shouldn't be too difficult to do.<br>
<br>
2. Should we migrate older datasets?<br>
<br>
This would allow us to compare existing datasets more accurately.
However this might have an effect on articles using embedded data.
For example if an article shows an amount of 100 EUR and is quoted
as such in the article, computing it to the current value (let's say
200 EUR) would create discrepancies between the data and the
article.<br>
<br>
We can avoid this if we let the computations for the current value
be optional and by default present the value at the time of the
data. I'm leaning towards this, but it might create inaccuracies
when comparing and presenting data. Users might not know about how
to present things at a current value and users might even expect
amounts to be presented in the current value. This is basically
another question:<br>
<br>
3. What should be the default presentation value?<br>
<br>
I would love for it to fit in with users' mental map but that might
create discrepancies for existing satellite sites and articles.<br>
<br>
4. What should be the base currency of openspending?<br>
<br>
We could define our own, e.g. GBP at 2011-07-19 (end of day value of
the main currency used by the first committer, nickstenning, at the
date of the first commit to github). We could also use a currency
like the SDR (special drawing rights) which is a currency created by
the IMF (defined by the weighted basket of the four major
currencies: US dollar, Euro, British pound, and the Yen). Date could
be date of implementation of the feature or whatever. We could also
use something like the US Dollar at unix timestamp 0 (1. january
1970). We could also use value of gold even though most currencies
today are floating currencies.<br>
<br>
From what I've read the US dollar has been used as a reference
currency around the world in recent years (at least since 1944 -
before that it was the British pound), The Yen came in at some point
but lost its traction around the Japanese recession. There are now
more Euros in the world than Dollars so people have been discussing
using the Euro as reference currency.<br>
<br>
I have no idea what would be best and I have no idea how this is
usually done in practice. I feel this is just something we need to
decide and I'd like your input on this.<br>
<br>
5. Where do we get the exchange rates from?<br>
<br>
There are a few ways to get the exchange rates. One is to use
<a class="moz-txt-link-freetext" href="http://openexchangerates.org">http://openexchangerates.org</a> (they have a simple json based api, 164
currencies, and historical rates reaching back to 1999). However
they charge for their api requests. We could scrape it ourselves
from websites and put up a conversion service ourselves. There might
be other sources I don't know about. Any suggestions?<br>
<br>
There are probably more questions that need answers, but let's start
with these. All input is greatly appreciated.<br>
<br>
<div class="moz-signature">-- <br>
<p>Tryggvi Björgvinsson</p>
<p>Technical Lead, OpenSpending</p>
<p>The <a href="http://okfn.org">Open Knowledge Foundation</a></p>
<p><i>Empowering through Open Knowledge</i></p>
<p><a href="http://okfn.org/">http://okfn.org/</a> | <a
href="http://twitter.com/OKFN">@okfn</a> | <a
href="https://facebook.com/OKFNetwork">OKF on Facebook</a> | <a
href="http://blog.okfn.org/">Blog</a> | <a
href="http://okfn.org/about/newsletter">Newsletter</a></p>
</div>
</body>
</html>
--------------040806070800010107010103--
More information about the openspending-dev
mailing list