From two different comments on here: http://stackoverflow.com/questions/5689369/what-is-the-diffe...

   Precision is the number of significant digits. Oracle guarantees the
   portability of numbers with precision ranging from 1 to 38.

   Scale is the number of digits to the right (positive) or left (negative)
   of the decimal point. The scale can range from -84 to 127.

Worth noting this isn't specifically an Oracle thing, most financial systems need to be sure that it can store currency numbers accurately and this convention is widely used to ensure this.

And:

   Precision 4, scale 2: 99.99

   Precision 10, scale 0: 9999999999

   Precision 8, scale 3: 99999.999

   Precision 5, scale -3: 99999000

Typically when dealing with currencies scale is only used to represent the units less than whole unit of the currency, i.e. cents and pence. But there isn't anything that restricts it from being used to accommodate larger numbers with the use of negative scales.

A current list of all ISO 4217 codes and the currency properties can be found here http://www.currency-iso.org/en/home/tables/table-a1.html

i.e.

   <CcyNtry>
      <CtryNm>UNITED STATES OF AMERICA (THE)</CtryNm>
      <CcyNm>US Dollar</CcyNm>
      <Ccy>USD</Ccy>
      <CcyNbr>840</CcyNbr>
      <CcyMnrUnts>2</CcyMnrUnts>
   </CcyNtry>

The CcyMnrUnts property denotes 2 decimal places for the sub-unit of the dollar.

So for the above example of 99999.999 you would store an amount of 99999999 and a scale of 3.

I guess "scale" here is log10 of the multiplier used in storing "amount".

So to convert the value back into the currency range, you're supposed to compute "amount / 10^scale".

So that it can be an integer with an arbitrary length, or a float/double without precision problems. You can also let our own integer classes do the parsing (which might even be able tonhandle complex types).

After all, everything in JSON is a string since it doesn't have a binary format and it shouldn't cause a huge overhead to do the parsing yourself (that might depend on the library, though).