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Ontology Usage

I.Edward Shaya, Brian Thomas, Zenping Huang, Peter TeubenUniversity of Maryland

THE US NATIONAL VIRTUAL OBSERVATORY

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Outline

• Our Project : 2-3 years in development, detail various potentially valuable uses for the VO, tested some sue cases, and developing a framework for use in the VO

• Outline– What can Ontologies do (that is useful to

VO) ?– One use case example we work with– Our Project Technologies

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Basic Ontology Properties

• * Depicts (Sub)classes, Properties of Classes, Domain and Range of Properties, and Instances.

• * Subclasses can have restrictions on ranges of properties or additional properties.

• * Equivalency of Classes, Sameness of Instances, Disjointedness, unions,

• * Ranges can have Restriction of AllValuesFrom, SomeValuesFrom, and Cardinality

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Obvious Uses

• Explicit statement of terms and relationships between terms. Similar to a data dictionary but expressed as a directed graph.

• UCD usage: connect an element with semantic meaning.

• Applications become aware of “isa” relations: SBc isa SpiralGalaxy, SpiralGalaxy isa Galaxy, TTauri isa Star.

• Aid to translating terminology between interest groups.

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No So Obvious Uses

• Allow for multiple relationships between a pair of Classes.– In XSD, GC/Star means GlobularCluster has

Star. But in ontology • GC1 hasForeground Star1• GC1 hasBackground Star2• GC1 hasMember Star3• GC1 hasLineOfSite Star4 • Or• Region Definedby GC1 has Star4

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Not So Obvious Uses (2)

• Clearly express Catalog’s domainGalaxy “Milky Way” hasMember “Messier 3”GlobularCluster “Messier 3” hasMember “CatalogRow”hasMeasurement ProperMotion=“pmM3”Star “CatalogRow” hasMeasurement ProperMotion=“pmStars”“pmStars” inInterval “pmM3”

This is a way to express that the catalog is one of stars that are members of M3 and M3 is in the Milky Way and membership is confirmed by proper motion.

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No So Obvious Uses (3)

• In tandem with the proper catalog DM it can provides a High Level Query Language:

– /MilkyWay//GlobularCluster//Star/hasVelocity//Amplitude/Value > 35 kmPerSec

• Provides descriptions of transforming between different representations of data. Such as from vector components to amplitude,direction.

• Ensures valid unit types on each Measurement. i.e. Force must have ForceUnits, Mass must have MassUnits.

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Example Use Case

Use-case: Finding the Hubble constant observationally.User wants distances and redshifts (cz) for various galaxy data.

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Ontology Snipet for Use-case

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Example Use Case (2)

Step 1: The Setup - specify the problem Galaxy (D, Cz)

Step 2: Inference engine does initial searchmatches:

Galaxy (D, Cz) SpiralGalaxy (D, Cz)

Galaxy (Dtf, Cz) SpiralGalaxy (Dtf, Cz)

Galaxy (Dceph, Cz)

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Example Use-case (3)

Step 3: User makes selection of appropriate objects. F(for this example we follow only one choice):

SpiralGalaxy (Dtf, Cz)

Step 4: Inference engine examines functional ontology to determine if indirect matches exist. Finds that :

Galaxy (Dtf, Cz ) <-> Galaxy (W20, Imag, incl)

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Example Use-case (4)

Step 5: User presented with the following set of semantic data definitions that can be used to search the VO repositories.

SpiralGalaxy (Dtf, Cz )

SpiralGalaxy (W20, Imag, incl)

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Ontology Tech we use (right now)

• Jena2 (Java) inference engine• OWL (W3C standard) for expressing

ontologies• Protege : lots of consistency checks,

visualization, etc to speed ontology construction

• True Grit

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Summary

• Started work on ontology approach to data discovery. Limited (so far) piecemeal success. – Working on how a unifying framework should

look like. – User GUI interface.

• Created initial ontology (at http://archive.astro.umd.edu/ont)

• Not exploiting all the possible uses (yet). Could be aiding discovery better.