QUDTAn OWL Ontology for

Quantities, Units, Dimensions and Data Types

Han WangApril 3rd, 2013

2

Introduction

• Developed by TopQuadrant and NASA for NASA Exploration Initiatives Ontology Models (NExIOM) project.

• A unified model of physical quantities, units of measure, and their dimensions in various measurement systems.

4/3/13

3

Classes

4/3/13

http://qudt.org/

4

Classes – cont’d

• Quantity– An observable property of an object, event or

system that can be measured and quantified numerically.

– Differentiated by two attributes: quantityKind and quantityValue.

– If two quantities are of the same kind, their magnitudes (values) can be compared and ordered.

4/3/13

5

Classes – cont’d

• QuantityKind– Any observable property that can be

measured and quantified numerically.– E.g. length, mass, currency, interest rate, etc.

• QuantityValue– The numerical value of a quantity with

respect to a chosen unit of measure.

4/3/13

6

Classes – cont’d

• Unit– A particular quantity of a given kind that has

been chosen as a scale for measuring other quantities of the same kind.

4/3/13

7

Classes – cont’d

• SystemOfQuantities– A set of one or more quantity kinds together

with a set of zero or more algebraic equations that define relationships between quantity kinds in the set.

– E.g. SI system, CGS system– Base quantity kinds (e.g. length, mass, time)– Derived quantity kinds (e.g. area, force,

power)

4/3/13

8

Classes – cont’d

• SystemOfUnits– A set of units which are chosen as the

reference scales for some set of quantity kinds together with the definitions of each unit.

– Base units (e.g. meter, kilogram, second)– Derived units (e.g. square meter, newton,

watt)

4/3/13

9

Classes – cont’d

• Dimension– a mapping from a tuple of rational numbers

to a product of base quantity kinds such that the tuple members correspond to the exponents of the base quantity kinds.

– E.g. A = L2, F = L1M1T-2, P = L2M1T-3

– dim Q = (B1)d1(B2)d2…(Bn)dn

4/3/13

10

Examples

• Value of Planck’s Constant in SI and CGS Units

4/3/13

11

Examples – cont’d

• Dimensions for Permittivity

4/3/13

12

Applications: SPIN Functions

• Unit conversion

4/3/13

13

Applications: SPIN Functions – cont’d

• Unit conversion

4/3/13

14

Conclusion

• A straightforward model for representing physical quantities.

• Capable of rule-based inference.• Not so much on metadata of the

quantities.

4/3/13

15

References

• http://qudt.org/• http://ontolog.cim3.net/file/work/UoM/

UoM-standard-ontology_20090924/QUDT-overview--JamesMasters_20090924.pdf

• http://linkedmodel.org/catalog/qudt/1.1/

4/3/13