Scientists have standardized on the SI unit system since the late 1700’s. While much work has been done over the years to refine and redefine the system, little has formally done to standardize the representation of the SI units in electronic systems. This paper will present a summary of current efforts toward electronic representation of scientific units in text, XML, and RDF, an analysis of needs for current computer/network systems, and an outline of future work.

1. Scientific Units
in the Electronic Age
Stuart J. Chalk, Department of Chemistry
University of North Florida
schalk@unf.edu
CINF Paper 49 – 251st ACS Meeting Spring 2016
#ACSCINFDataSummit

2.  Why Do Computers Need to Know About Units?
 What Do We Need?
 Unit Systems
 Implementation of
Units for Computers
 Text Units
 XML Units
 Semantic Units
 What We Really Need
 Things To Do
 Conclusion
Outline
From: http://unitsml.nist.gov/Presentations/UnitsML_for_TC.pdf

4.  Computers are used to represent data
 Data is not useful unless it has a context – meaning
 Part of the context of data is its unit of measure
 Publication of scientific data – it needs definitive units!
Why do Computers
Need to Know About Units?
From: http://www.slideshare.net/petermurrayrust/text-and-data-mining-explained-at-ftdm

5. What Do We Need?
 A way to uniquely identify and give meaning to units…
 …and dimensions, quantities, properties(?)
 A way to uniquely identify and give meaning to fundamental
constants and conversion factors
 Must describe the semantics of prefixes
 Must accommodate all languages (spoken and computer)
 Must be usable at different levels of technology
 Must be unit system agnostic
 Must be as future-proof as possible (extensible/adaptable)

6. What Do We Need?
 A standards organization to host a platform providing
unambiguous representations of any unit of measure
 Tools/services to allow identification of units that can be
used to represent the same quantity
 Tools/services to allow systems to interconvert units and
provide a mechanism to document the conversion
 Must be compliant with the tools/services supporting big
data and the semantic web

7. From: http://physics.nist.gov/cuu/pdf/SIDiagramColor.pdf

8.  International System of Units (SI)
 Including CGS and MKS
 UK Imperial System
 US Customary Units
 Burmese
 Indian
 Astronomical Units
 Troy (mass) Units
 Historical/Obsolete Units and Unit Systems
https://en.wikipedia.org/wiki/List_of_obsolete_units_of_measurement
Unit Systems

9. Implementations of
Units for Computers
 Text String
 XML (Tagged Text)
 Semantically (URI)

10.  International Virtual Observatory Alliance (IVOA)
http://www.ivoa.net/documents/VOUnits/
 Standardization of string representations of unit
labels (“VOUnits”) in the astronomy community
Text String Representation
From: http://www.ivoa.net/documents/VOUnits/20140523/VOUnits-REC-1.0-20140523.pdf

11.  MathML (https://www.w3.org/TR/mathml-units)
 Presentation of Units
 Unit Symbols in Content MathML
 Conversion
of Units
XML Representation
<apply>
<divide/>
<csymbol definitionURL='http://.../units/meter#c>cm</csymbol>
<csymbol definitionURL='http://.../units/second>s</csymbol>
</apply>
<apply>
<times/>
<csymbol definitionURL='http://.../units/meter#c>cm</csymbol>
<apply>
<power/>
<csymbol definitionURL='http://.../units/second>s</csymbol>
<cn type='integer'>-1</cn>
</apply>
</apply>
<csymbol definitionURL='http://.../units/kyne'>kyn</csymbol>

12.  Geographic Markup Language (GML)
http://www.opengeospatial.org/standards/gml
 Provides
 Unit References (“unitOfMeasure” element)
 Unit Definitions (“unitDefinition” element)
 “BaseUnit”, “DerivedUnit”, and “ConventionalUnit”
XML Representation
<gml:DerivedUnit gml:id="m3">
<gml:identifier codeSpace=“…/?iid=79">cubic metre</gml:identifier>
<gml:quantityType>Volume</gml:quantityType>
<gml:derivationUnitTerm uom="#m" exponent="3"/>
</gml:DerivedUnit>

13.  Scientific, Technical, and
Medical Publishing (STTML)
Part of the Chemical Markup Language (CML)
http://cml.sourceforge.net/schema/
XML Representation
<stm:unit id="second" name="second" unitType="time">
<stm:description>The SI unit of time</stm:description>
</stm:unit>
<stm:unit id="newton" name="newton" unitType="force”>
<stm:description>The SI unit of force</stm:description>
</stm:unit>
<stm:unit id="g" name="gram" unitType="mass" parentSI="kg" multiplierToSI="0.001"
abbreviation="g”>
<stm:description>0.001 kg.</stm:description>
</stm:unit>
<stm:unit id="inch" name="inch" parentSI="meter" abbreviation="in" multiplierToSI="0.0254" >
<stm:description>An imperial measure of length</stm:description>
</stm:unit>

14.  UnitsML
http://unitsml.nist.gov/
 NIST Project
– intended to be published as a standard under OASIS
 Fundamental representation of dimensions, units, quantities
 UnitsDB a symbiotic project (internal to NIST)
 Never formally standardized under OASIS…
…and NIST ran out of funding
XML Representation

15. XML
Representation
From: http://www.oasis-open.org/committees/download.php/42538/UnitsML-Guide-v1.0-wd01.pdf

16. XML Representation
From: http://www.oasis-open.org/committees/download.php/42538/UnitsML-Guide-v1.0-wd01.pdf

17. XML Representation
<units xmlns="http://units.nist.gov/2003/01/units/SI"
xmlns:q="http://units.nist.gov/2003/01/quantities"
xmlns:usym="http://units.nist.gov/2003/01/symbols/units”>
<unit commonName="meter" unitID="unit0001" symbol="m">
<system type="base">SI</system>
<name xml:lang="en-US">meter</name>
<name xml:lang="en-GB" >metre</name>
<name xml:lang="fr" >mètre</name>
<unitSymbolRef unitSymbolIDRef="usym:symbol0001">m</unitSymbolRef>
<quantityRef quantityIDRef="q:quantity0001" />
<history href="http://…">…</history>
<definition href="http://…">…</definition>
<remarks href="http://…">…</remarks>
</unit>
</units>

18. XML Representation
<quantity quantityID="quantity0001” commonName="length” type="base">
<name xml:lang="en-US">length</name>
<quantSymRef quantSymbolIDRef="qsym:symbol0001">l</quantSymRef>
<dimSymRef dimSymbolIDRef="dsym:symbol0001">L</dimSymRef>
<unitSIRef unitSIIDRef="SI:unit0001" />
</quantity>
<prefix prefixID="prefix0004" commonName="mega" symbol="M” power="6" system="SI"
base="10">
<name xml:lang="en-US" >mega</name>
<prefixSymbolRef prefixSymbolIDRef="psym:symbol0004" />
</prefix>
<dimensionSymbols xmlns="http://units.nist.gov/2002/01/symbols/dimensions" >
<dimensionSymbol dimensionSymbol ID="symbol0001" commonSymbol="L">
<symbolFont family="sans-serif" style="normal" weight="bold">L</symbolFont>
</dimensionSymbol>
<dimensionSymbol dimensionSymbol ID="symbol0005" commonSymbol="Θ">
<symbolFont family="sans-serif" style="normal" weight="bold">Θ</symbolFont>
</dimensionSymbol>
</dimensionSymbols>

19.  “Semantics” - the branch of linguistics and
logic concerned with meaning
 Rather than just identify a unit,
indicate the meaning of a unit
 Resource Description Framework (RDF)
 Subject-Predicate-Object “triples”
 RDF-XML (https://www.w3.org/TR/rdf-syntax-grammar/)
 JSON-LD (JSON for Linked Data)
 Ontological Definitions
Semantic Representation

20.  Units of Measure Ontology (UO)
https://github.com/bio-ontology-research-group/unit-ontology
http://www.ontobee.org/ontology/UO
Semantic Representation

21.  Semantic Web for Earth
and Environmental
Technology (SWEET)
http://sweet.jpl.nasa.gov/
 “SWEET 2.3 is highly modular
with 6000 concepts in 200
separate ontologies.”
Semantic Representation

22.  Quantities, Units, Dimensions and Data Types Ontology (QUDT)
 Version 1
http://www.qudt.org/
 Version 2
http://www.linkedmodel.org/doc/2015/DOC_schema-qudt-v2.0
 Space Time Vocabulary
http://qudt.org/vocab/unit/units-space-and-time.html
 Physical Chemistry and Molecular Physics Vocabulary
http://qudt.org/vocab/unit/units-physical-chemistry-and-
molecular-physics.html
Semantic Representation

23. Semantic Representation

24. Semantic Representation

25. Semantic Representation

26. Semantic Units Model
From: http://www.allhands.org.uk/2006/proceedings/papers/614.pdf

27. Semantic Units Model
From: http://www.allhands.org.uk/2006/proceedings/papers/614.pdf

28. Semantic Units Model
From: http://www.allhands.org.uk/2006/proceedings/papers/614.pdf

29.  A Metrology Ontology!
What Do We
Really Need?
From: http://ontology.iupac.org/ontology.pdf

30. Official Metrology
Definitions
From: http://www.bipm.org/utils/common/documents/jcgm/JCGM_200_2012.pdf

31.  Write up a summary of current state of units
 Develop a proposal to implement units in computers based on
best features of existing work
 Development of a metrology ontology
(33 results on google – none are a general ontology for metrology)
 Evaluate support technology needed to implement the ontology
 Identify specific use cases and implement solutions
 Formalize as a standard, with use cases and example
implementations
 Applicable for text, XML, and Semantic formats…
 ...databases, ELNs, instrument software,
Things To Do

32.  schalk@unf.edu
 Phone: 904-620-5311
 Skype: stuartchalk
 LinkedIn/Slidehare: https://www.linkedin.com/in/stuchalk
 ORCID: http://orcid.org/0000-0002-0703-7776
 ResearcherID: http://www.researcherid.com/rid/D-8577-2013
Questions?