Native support for units

[siljamardla]

When working with certain types of metrics, it becomes rather tedious to maintain metrics in different units. Some examples include:

• durations (in seconds, minutes, hours etc)
• distances (in meters, km, miles etc)

At the moment, the only option would be to define separate metrics. The risk is that their definitions will go out of sync. And we need to use some naming convention to make it easy for users to work with the different units.

Ideally, units would be something that is natively supported and it would be enough to define something like this:

name: distance_to_customer
unit: meter

At query time, it would then be possible to specify another unit and the outcome would be automatically converted. After all, the conversion equation from meters to kilometers will be absolutely stable and uniform across the world :)

[jaakla]

With the Semantic Type proposal (#55 and more detailed semantic field types) I've tried to provide "higher level" solution which allows to describe semantics of any field, so numeric measurements like distances have distance units (meters), financial measurements like prices currencies etc.

[thadguidry]

ISO/TC 12 as well as UCUM and QUDV should be consulted.