has its own quirks.

Greenwich mean time (GMT) is the time that occurs at the meridian that runs through
Greenwich, England. The good news about GMT is that there is universal understanding
as to what that time is. The bad news is that it is not in agreement with 23 other time
zones in the world. But at least, there is an agreed-upon understanding of time in at least
one other place in the world.

Julian date is the sequential count of dates starting from day 0, which occurred at Jan 1,
4713 BC. The value of Julian date is that it is universal and that it reduces the number of
days to an ordinal number. In a standard calendar, calculating how many days there are
between 16 May 2014 and 3 Jan 2015 is a complex thing to do. But with Julian date, such
a calculation is very simple to do.

The US dollar is as good a measurement of currency as any other measure. But even with
the US dollar, there are challenges. For example, the conversion rate between the dollar
and other currencies is constantly changing. If you calculate a value on Feb 15 converting
the dollar against another currency, chances are excellent that you will get a different
value if you make the same currency conversion on Aug 7. But all other factors being
equal, the US dollar serves as a good economic measurement of wealth.

Fig. 9.3.2 shows some of the universal measurements.

Fig. 9.3.2 Some standard measurements of data.

Security

Another significant and serious concern of data (anywhere, not just in big data) is that of
security. There are literally hundreds of reasons why data need to be secure:

Chapter 9.3: Repetitive Analysis