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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>

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    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 Bj&ouml;rgvinsson</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>
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