Come to meet JSR 363 - Units of Measurement! It's the first JSR targeted to help you work with IoT devices, tackling sensors and measurements in a standard way. We all know that when representing a temperature, for example, we normally have it as a float. But, is this float in Celsius? Fahrenheit? Kelvin? This is one of the problems this JSR wants to solve: have all "real world" value and unit data represented in a standard way. This JSR is also very suitable for scientific applications, where data representation, conversion and formatting is very important. In this presentation, we'll see how both developers and platform providers can leverage this JSR, coding for a smart home or smart gas pump that reports its values in a standard way. As well as other use cases and actual embedded devices like Raspberry Pi or Intel Edison. And this JSR is still in the making. Be first hand witness of the JSR 363 Public Draft (due around Nov) and learn how YOU can get involved and help Java grow in the IoT space! We'll explore how JSRs work and how you can get involved in the JCP and work with this and other JSRs.

1. @UnitAPI#JSR363
The First IoT JSR: Units of Measurement
JSR-363
Werner Keil | Otávio Santana
@wernerkeil | @otaviojava
@UnitAPI
https://www.jcp.org/en/jsr/detail?id=363
http://unitsofmeasurement.github.io

2. @UnitAPI#JSR363
What is JSR-363?
6,370.98 miles
A Quantity
A Unit

3. @UnitAPI#JSR363
Why do we need JSR-363?
There are no specifications or standards for handling units in Java.
The current solution is to use primitives, that don’t provide any Type
Safety.
The errors are difficult to find using unit testing:
Interface and Internationalization (e.g. radian/degree, meters/feet);
Arithmetic operations (e.g. overflow);
Conversion between units (e.g. from same domain);

4. @UnitAPI#JSR363
What is JSR-363?
Interfaces and abstract classes supporting unit operations including:
Checking of unit compatibility;
Expression of measurement in various units; and
Arithmetic operations on units.
Concrete classes implementing standard unit types (base, derived), unit
conversion and representation.
A framework supporting robust representation and correct handling of
quantities.
JSR 363 establishes safe and useful methods for modeling physical
quantities.

5. @UnitAPI#JSR363
System of Units
System International d’Unites (SI)
The accepted basis for most scientific and engineering
activities.
Standard units for key physical quantities
(length, time, power etc.)
Standard prefixes
(kilo/micro etc.)
Standard dimensions…

6. @UnitAPI#JSR363
Dimension
Allows analysis of a quantity by the rational powers of the 7 fundamental
dimensions (quantities are compatible when they have the same
dimensions):
length (L), mass (M), time (T), electric charge (I), absolute temperature
(Θ), amount of substance (N) and luminous intensity (J)
Examples:
Speed = length/time - it’s dimensions are L=1,T=-1 (rest 0) (e.g. metre/second - ms-1)
Acceleration is speed/time (m/s/s or ms-2) L=1, T=-2
Force is mass x acceleration M x ((length/time)/time) or M=1, L=1, T=-2
Molar Entropy: M=1 L=2 T=−2 Θ=−1 N=−1 (trust me!)

7. @UnitAPI#JSR363
Quantity
A physical attribute of a thing. Something that can be measured and has
units. Compatible quantities have the same dimension…
Examples:
• Time
• Length
• Speed
• Amount of Substance
• Luminous Intensity
• Volume
• Mass
• Force
• Power
• Electrical Current
• Magnetic Flux Density
• Volumetric Flow Rate
• Fuel Economy*
• Percentage
• Eggs per carton
• Sheep per hour
• Bits and bytes …
… ∞

8. @UnitAPI#JSR363
Unit Conversion
The process of conversion depends on the specific situation and the
intended purpose. This may be governed by regulation, contract,
technical specifications or other published standards.
Wikipedia

9. @UnitAPI#JSR363
1983: The Gimli “Glider”
Photo: Wayne Glowacki
Maintenance workers performed a test that estimated that 7,682 litres of
fuel were in the tank. They knew they needed 22,300 kilograms of fuel
for the remaining flight, so the question was, How much fuel, in litres,
should be pumped from the fuel truck into the aircraft? They were
forced to resort to a manual calculation:
They multiplied 7,682 L by 1.77, the density of the fuel provided by the
refuelling company on their documentation: The aircraft, according to
their calculations, currently had 13,597 kg of fuel.
Subtracting from 22,300 kg, they decided they needed to add 8,703 kg of
fuel.
Dividing by 1.77 — the same density used in the previous calculation —
yields 4,916 L, which was pumped into the aircraft.
However, 1.77 was the density of the fuel in pounds per litre (lb/L), not
kilograms per litre (kg/L); the correct figure for kg/L would have been
0.80. As a result, they ended up with less than half of the required
amount of fuel on board. (The fuel's density depends on
characteristics of the fuel, so it's not a constant, and the value must
be taken from documentation accompanying the fuel.)

10. @UnitAPI#JSR363
Some real-life mishaps…
[Cost $125M]
“Preliminary findings indicate that one team used US/English units (e.g.
inches, feet and pounds) while the other used metric units for a key
spacecraft operation.”
NASA Mars Climate Orbiter, 1999

11. @UnitAPI#JSR363
Conversion problems
These are examples of confusion on the units in application.
But there is also ambiguity on the unit itself:
10 Gallons … Gallon Dry / Gallon Liquid - Gallon US / Gallon UK
28 Days … Day Sidereal / Day Calendar
38 Degrees … Degree Celsius / Degree Fahrenheit / Degree Angle
And the wrong conversion factors:
static final double PIXEL_TO_INCH = 1 / 72;
double pixels = inches * PIXEL_TO_INCH;

12. @UnitAPI#JSR363
What is the problem, in code?
float distance = 6370.98; //in miles
float speed = airplane.getSpeed(); //in km/h
System.out.println(“TTD: “ + (distance/speed) + “ h”);
6,370.98 miles
A Quantity
A Unit

13. @UnitAPI#JSR363
What is JSR-363, in code?
Quantity<Length> distance =
Quantities.getQuantity(6370.98, USCustomary.MILE);
Quantity<Speed> airplaneSpeed = getAirplaneSpeed();
Quantity<Time> timeToDest =
(Quantity<Time>)distance.divide(airplaneSpeed);
System.out.println(“TTD: “ + timeToDest.to(Units.HOUR));
TTD: 10.84983093613525 h

14. @UnitAPI#JSR363
Who is going to use JSR-363?
Java developers who work with physical quantities need to handle
measurements in their programs.
Inadequate models of physical measurements can lead to significant
programmatic errors.
Platform providers and developers can provide and use a more
well-defined API.
Embedded developers can have less error-prone, more self-
documented code.

15. @UnitAPI#JSR363
JSR-363: Internal Structure
JSR-363 is broken down into the following packages:
Package Description
javax.measure Core API interfaces (e.g. Dimension, Quantity, Unit)
javax.measure.format [optional] Interfaces for quantity/unit formatting and parsing
javax.measure.quantity [optional] Interfaces for quantity types (e.g. Mass, Length)
javax.measure.spi [optional] Service Provider Interface (implementation discovery)
Reason: We target very small devices running Java ME (CLDC 8) for IoT
applications (e.g. sensors, wearables, gateways etc.)

16. @UnitAPI#JSR363
JSR-363: Systems and
ExtensionsOn top of JSR-363 we offer support
for various unit systems:
• Reusable Quantities
• SI System
• Common Systems (US, Imperial)
• ISO 80000
• UCUM
Reason: By providing small, modular
libraries, we live and sometimes forestall
the ideas behind Java ME 8 or Jigsaw and
offer great flexibility to IoT solutions

17. @UnitAPI#JSR363
JSR-363 timeline
March 11, 2014: Submitted
April 7, 2014: Creation approved
Dec 2014 – January 2015: Early Draft (done)
Q3/2015 – Q4/2015: Public Review (approved)
Q2/2016 : Final Draft
Q3/2016 : Final Release

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19. @UnitAPI#JSR363
Links to JSR-363
Public mailing list(s) and/or forum(s)
Units-Dev on Google Groups
Units-Users on Google Groups
EG only mailing list on java.net, archive fully visible (while java.net
exists)
JSR detail page on JCP.org: https://www.jcp.org/en/jsr/detail?id=363
Project website on GitHub: unitsofmeasurement.github.io

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