Ontology of astronomical object types

Introduction

This page summarizes efforts on the construction of an ontology of astronomical object types. The starting point is the Object Classification that is used in SIMBAD: a list of approximately 100 concepts that are used as labels for individual astronomical objects in SIMBAD.

The ontology's main features are :

• it is an ontology of defined concepts (i.e. the concepts are defined by a set of necessary and sufficient conditions) which enables automatic reasoning
• it is implemented in the OWL 1.1 language (recent evolution of OWL-DL), but currently the complexity of the structure is still within the OWL-DL boundaries.

Concepts

The ontology contains a few top-level concepts which are:

AstrObject

subsumes all the concepts representing astronomical objects

AstroPortion

subsumes all the concepts representing portions of astronomical objects which are not astronomical objects themselves

AtomicElement

Atomic elements

ClassificationCategory

root concept for all kinds of classes used in objects desciption (e.g. spectral class)

EMSpectrumRange

sets of ranges in the electromagnetic spectrum

Measurement

measured observational parameters/properties

Morphology

geometry or morphology of astronomical objects (including non-astronomical object components)

Process

phenomenom or associated process

Additionally, a top-level concept called Test_classes can be found in some versions of the ontology file : it contains all the concepts used for tests (e.g. new concepts to classify to test the classification engines)

Properties

The following properties have been used in the ontology:

Object properties

name	domain	range	inverse	transitive	description
hasEmissionIn	AstrObject	EMSpectrumRange	---	no	The Astronomical object emits in the EM range specified
hasAbundanceOf	AstrObject	AtomicElement	---	no
hasMeasurement	AstrObject	Measurement	isMeasuredFor	no	Indicates that the DOMAIN AstrObject has the RANGE Measurement among its (observational) measurements
isMeasuredFor	Measurement	AstrObject	hasMeasurement	no
hasProcess	AstrObject	Process	---	no	Indicates that an astronomical object is the location of a Process/has an attached process
hasPortion	AstrObject OR AstroPortion	AstroPortion	isPortionOf	no
isPortionOf	AstroPortion	AstrObject OR AstroPortion	hasPortion	no
hasMorphology	AstrObject	Morphology	isMorphologyOf	no
isMorphologyOf	Morphology	AstrObject	hasMorphology	no
hasComponent	CompoundObject OR AstroPortion	AstrObject	isComponentOf	yes	Indicates that the DOMAIN CompoundObject has the RANGE AstrObject among its physical components (the RANGE AstrObject cannot be a component of a component of the compound object)
isComponentOf	AstrObject	CompoundObject OR AstroPortion	hasComponent	yes	Indicates that the DOMAIN AstrObject is a physical component of the RANGE CompoundObject (not a component of a component of the RANGE CompoundObject)
hasSpectralLine	AstrObject	AtomicElement	---	no
hasEmissionSpectralLine	AstrObject	AtomicElement	---	no
hasAbsorptionSpectralLine	AstrObject	AtomicElement	---	no
isIonizedBy	InterStellarMedium	EarlyTypeStar OR Shockwave OR PlanetaryNebulaCentralStar	---	no
hasClassification	AstrObject	ClassificationCategory	isClassifiedAs	no
isClassifiedAs	ClassificationCategory	AstrObject	hasClassification	no
hasProgenitor	Supernova	WhiteDwarf OR WolfRayetStar OR HighMassStar	---	no

Datatype properties

None

Annotation properties

Some annotation properties are used to store references to concepts in existing applicationt

name	description
adc:keyword	Astronomical Data Center keyword
gcvs:code	General Catalogue of Variable Stars code corresponding to a concept of the ontology
interface:naturalName	name in natural language for display purposes
interface:searchKeywords	keywords for search purposes
interface:unit	the unit associated with the value of an instance of measturement
interface:values	The operators and values for an instance (of measurement)
misc:description	textual description/definition of a concept
misc:externalTests	tests that should be taken care of outside of the ontology (e.g. check that a value is within sensible boundaries)
ned:code	object type code in NED
simbad:name	Standard name in SIMBAD's object classification
simbad:shortCode	Short code in SIMBAD's object classification
simbad:luminosityClass	Main part of the luminosity class in SIMBAD (letters only, found within SIMBAD's spectral type value after said spectral type)
simbad:morphologicalType	morphological type for galaxies in SIMBAD
simbad:spectralType	Main part of the spectral type in SIMBAD (letters only, found at the beginning of SIMBAD's spectral type value)
vizier:keyword	VizieR registry keyword

Technical issues

Choices and lessons learned during the construction of the ontology.

Protégé issues and advice

The Protégé editor is a great tool for building ontologies but some ProtegeAdvice helps to face a few potential problems

Note: the DLSyntaxDisplay option the OWL>preferences menu was bugged for a lot of revisions until ver. 3.3 and may even lead to data loss! So if you want a DL-like syntax representation of restrictions on properties, select the CompactOWLClassDisplay instead. Else, keep the ManchesterDisplay, it is the safest of all.

OWL flavours

The Web Ontology Language is availiable in 3 (soon 4) flavours based on differents DescriptionLogics :

flavour	description logic	decidable	comment
OWL-Lite	SHIF(D)	yes	least expressiveness of the OWL flavours, least resource-consuming
OWL-DL	SHOIN(D)	yes	a lot more expressive, more resource-consuming but still decidable
OWL-1.1	SHROIQ(D)	yes	revision of OWL-DL, adds qualified cardinality restrictions and more expressivity on roles, even heavier resource-wise but decidable
OWL-Full	beyond SHROIQ(D)	no	No limit on expressiveness, only subsets are decidable

Various inference engines

We have performed various InferenceEngineTests.

The most efficient reasoners available for description logics are the following. All are based on different description logics and implementations.

reasoner	test version	logic	implementation	license	comments
RACER	1.7.24	SHRIQ(D)	CommonLISP	free license	discontinued since 1.7.24 (authors went commercial with RacerPro)
RacerPro	1.9	SHRIQ(D)	LISP	commercial	DIG-only interface doesn't need a commercial license
FaCT++	1.1.3	SHOIQ(D)	C++	GPL	difficulties with large-scale hierarchies
Pellet	1.3	SHOIN(D)	Java	M.I.T. (free)	Theoretically now supports SHOIQ(D) but Qualified Cardinality is not really supported yet, difficulties with large-scale hierarchies
Pellet	1.5.2	SHOIQ(D)	Java	M.I.T. (free)	Even more powerful than RACER 1.7.24, good support, implements configuration flags to simulate assumptions such as closed world or unique name

The tests compared the performances of the different reasoners for the following tasks :

• checking the consistency of the ontology
• classifying the ontology

Conclusions:

• (Given the expressiveness we need RACER/RacerPro was the best option until the release of Pellet 1.4. RacerPro being commercial, prices and possible incompatibility with some API (e.g. Jena) might be a problem. Basically, the best option is RACER 1.7.24 since it's free and, though discontinued, has both good performance and extensive compatibility with the OWL APIs) *Currently, Pellet seems much more interesting than RACER since it has basically the same level of DL handling, similar if not better performance and obviously better support
• To limit complexity, existential restrictions (\exist R C) are to be used instead of qualified cardinality (\geq n R C) or (\leq n R C) whenever possible.

Download

The following versions of the ontology can be dowloaded for testing. Most recent files are on top of the table.

Release date	Files (owl, pprj)	Changes	Protégé version

2008/09/05	ObjectTypes_0.99y.owl	Even simpler DL (ALCIN instead of SIQ(D) )more conditions expressed backward, NED keywords as annotation	3.4 build 506
2008/06/06	ObjectTypes_0.99s.owl	Simpler DL (SIQ instead of SHOIQ), annotations include ADC and VizieR keywords	3.4 build 501
2008/02/06	ObjectTypes_0.99a.owl	new annotations, more and better backwards conditions	3.4 build 125
2007/10/06	ObjectTypes_0.98b.owl	enhanced branches and new annotation properties	3.3.1 build 430
2007/02/23	ObjectTypes_0.85.owl	corrected and optimized	3.2 build 355
2007/02/13	ObjectTypes_0.84.owl	Extended and optimized	3.2 build 355
2007/01/29	ObjectTypes_0.83.owl	Revamped, improved and extended	3.2 build 355
2006/09/04	CloneCompliant44.owl	Version used to test the registry request builder	3.2 build 324
2006/07/17	CloneCompliant41.owl	Re-structured skeleton	3.2 build 324
2006/06/07	CloneCompliant19.owl	First public version	3.2 build 322

Applications

Details of OntologyUseCases for the ontology of astronomical object types are available on the OntologyOfObjectTypesUseCases page.

Links

• List of SIMBAD object types
• The Protégé editor
• A summary of OWL 1.1
• The Pellet reasoner home page
• IVOA Technical Note - Ontology of Object Types v1.1 AstrObjectOntology-20080716.pdf

-- AlexandreRichard - 01 Jun 2006