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A Quick Introduction to OWL Web Ontology Language

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  1. A Quick Introduction toOWL Web Ontology Language Roger L. Costello David B. Jacobs The MITRE Corporation (The creation of this tutorial was sponsored by DARPA)

  2. What is OWL? Answer: OWL is a set of XML elements and attributes, with standardized meaning, that are used to define terms and their relationships. OWL extends RDF Schema: Class equivalentProperty sameIndividualAs ... OWL OWL elements and attributes (i.e., OWL Vocabulary) subClassOf resource ID ... RDF Schema

  3. Example of using OWL to define two terms and their relationship Example: Define the terms "Camera" and "SLR". State that SLRs are a type of Camera. Here's how these two terms (classes) and their relationship is defined using the OWL vocabulary: <owl:Class rdf:ID="Camera"/> <owl:Class rdf:ID="SLR"> <rdfs:subClassOf rdf:resource="#Camera"/> </owl:Class>

  4. Quick Intro Contents • In this quick intro we present an example to demonstrate one of the utilities of OWL: • The example shows how OWL can be used to bridge terminology differences and thus enhance interoperability.

  5. Example: Bridging the Terminology Gap using OWL • A key problem in achieving interoperability is to be able to recognize that two pieces of data are talking about the same thing, even though different terminology is being used. • The following slides presents an example to show how OWL may be used to bridge the "terminology gap".

  6. Interested in Purchasing a Camera • Scenario: • I am interested in purchasing a camera with a 75-300mm zoom lens size, that has an aperture of 4.5-5.6, and a shutter speed that ranges from 1/500 sec. to 1.0 sec. • I launch my personal "Web Bot" which crawls the Web looking for Web sites that can fulfill my request. • Assume that there exists an OWL Camera Ontology, which the Web Bot can "consult" upon its travels across the Web.

  7. Is this document relevant? <PhotographyStore rdf:ID="Hunts" xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"> <store-location>Malden, MA</store-location> <phone>617-555-1234</phone> <catalog rdf:parseType="Collection"> <SLR rdf:ID="Olympus-OM-10" xmlns="http://www.camera.org#"> <lens> <Lens> <focal-length>75-300mm zoom</focal-length> <f-stop>4.5-5.6</f-stop> </Lens> </lens> <body> <Body> <shutter-speed rdf:parseType="Resource"> <min>0.002</min> <max>1.0</max> <units>seconds</units> </shutter-speed> </Body> </body> <cost rdf:parseType="Resource"> <rdf:value>325</rdf:value> <currency>USD</currency> </cost> </SLR> </catalog> </PhotographyStore> The Web Bot finds this document at a Web site: Is it relevant? (Note: SLR = Single Lens Reflex)

  8. A Match? <PhotographyStore rdf:ID="Hunts" xmlns:rdf="&rdf;#"> <store-location>Malden, MA</store-location> <phone>617-555-1234</phone> <catalog rdf:parseType="Collection"> <SLR rdf:ID="Olympus-OM-10" xmlns="http://www.camera.org#"> <lens> <Lens> <focal-length>75-300mm zoom</focal-length> <f-stop>4.5-5.6</f-stop> </Lens> </lens> <body> <Body> <shutter-speed rdf:parseType="Resource"> <min>0.002</min> <max>1.0</max> <units>seconds</units> </shutter-speed> </Body> </body> <cost rdf:parseType="Resource"> <rdf:value>325</rdf:value> <currency>USD</currency> </cost> </SLR> </catalog> </PhotographyStore> I am interested in purchasing a camera with a 75-300mm zoom lens size, that has an aperture of 4.5-5.6, and a shutter speed that ranges from 1/500 sec. to 1.0 sec. Match? To determine if there is a match, these questions must be answered: 1. What's the relationship between "SLR" and "Camera"? 2. What's the relationship between "focal-length" and "size"? 3. What's the relationship between "f-stop" and "aperture"?

  9. Relationship between SLR and Camera? The Web Bot "consults" the OWL Camera Ontology. This OWL statement tells the Web Bot that a SLR is a type of Camera: <owl:Class rdf:ID="SLR"> <rdfs:subClassOf rdf:resource="#Camera"/> </owl:Class> "Relationship between Camera and SLR?" <PhotographyStore rdf:ID="Hunts" <SLR> … </SLR> </PhotographyStore> Web Bot <owl:Class rdf:ID="SLR"> <rdfs:subClassOf rdf:resource="#Camera"/> </owl:Class> "SLR is a type of Camera." Camera.owl Hunts.xml

  10. Relationship between focal-length and lens size? This OWL statement tells the Web Bot that focal-length is equivalent to lens size: <owl:DatatypeProperty rdf:ID="focal-length"> <owl:equivalentProperty rdf:resource="#size"/> <rdfs:domain rdf:resource="#Lens"/> <rdfs:range rdf:resource="&xsd;#string"/> </owl:DatatypeProperty> "focal-length is synonymous with (lens) size. focal-length is to be used within a Lens. focal-length has a value that is a string."

  11. Relationship between f-stop and aperture? This OWL statement tells the Web Bot that f-stop is equivalent to aperture: <owl:DatatypeProperty rdf:ID="f-stop"> <owl:equivalentProperty rdf:resource="#aperture"/> <rdfs:domain rdf:resource="#Lens"/> <rdfs:range rdf:resource="&xsd;#string"/> </owl:DatatypeProperty> The Web Bot now recognizes that the XML document it found at the Web site -is talking about Cameras, and it - does show the lens size, and it - does show the aperture for the camera, and - the values for lens size, aperture, and shutter speed are met. Thus, the Web Bot recognizes that the XML document is a match!

  12. Semantic Definitions Separate from Application! Semantic Definitions "Relationship between Camera and SLR?" <owl:Class rdf:ID="SLR"> <rdfs:subClassOf rdf:resource="#Camera"/> </owl:Class> <owl:DatatypeProperty rdf:ID="focal-length"> <owl:equivalentProperty rdf:resource="#size"/> <rdfs:domain rdf:resource="#Lens"/> <rdfs:range rdf:resource="&xsd;#string"/> </owl:DatatypeProperty> <owl:DatatypeProperty rdf:ID="f-stop"> <owl:equivalentProperty rdf:resource="#aperture"/> <rdfs:domain rdf:resource="#Lens"/> <rdfs:range rdf:resource="&xsd;#string"/> </owl:DatatypeProperty> <SLR rdf:ID="Olympus-OM-10" xmlns="http://www.camera.org#"> <lens> <Lens> <focal-length>75-300mm zoom</focal-length> <f-stop>4.5-5.6</f-stop> </Lens> </lens> <body> <Body> <shutter-speed rdf:parseType="Resource"> <min>0.002</min> <max>1.0</max> <units>seconds</units> </shutter-speed> </Body> </body> <cost rdf:parseType="Resource"> <rdf:value>325</rdf:value> <currency>USD</currency> </cost> </SLR> "SLR is a type of Camera." Web Bot (application) "Relationship between aperture and f-stop?" "f-stop is synonymous with aperture." "Relationship between size and focal-length?" Hunts.xml "focal-length is synonymous with size." Camera.owl See the article "Why use OWL?" for a discussion of why it is good practice to separate the semantic definitions from the application.

  13. Summary: Interoperability despite terminology differences! • The example demonstrated how a Web Bot application was able to dynamically process an XML document from a Web site, despite the fact that the XML document used terminology different than was used to express the request. This interoperability was achieved by using the OWL Camera Ontology! • This example also demonstrated the architectural design principle of cleanly separating the application code (e.g., Web Bot) from the semantic definitions (e.g., Camera.owl).

  14. Demo of interoperability in a heterogeneous data environment What do you know about SLR? Hunts.xml Camera Application SLR is a type of Camera. Camera.owl

  15. Demo - searching for Camera, lens size, aperture info • The Camera Application is searching for documents that meet this desire: • I am interested in purchasing a Camera with a 75-300mm zoom lens size, that has an aperture of 4.5-5.6, and a shutter speed that ranges from 1/500 sec. to 1.0 sec. • The Camera Application understands the terms (i.e., elements) Camera, lens size, and aperture. • If a document uses terms that it does not understand, then the Camera application "consults" the Camera Ontology.

  16. Hunts.xml - uses unfamiliar terminology <PhotographyStore> <catalog rdf:parseType="Collection"> <SLR rdf:ID="Olympus-OM-10" xmlns="http://www.xfront.com/owl/ontologies/camera/#"> <lens> <Lens> <focal-length>75-300mm zoom</focal-length> <f-stop>4.5-5.6</f-stop> </Lens> </lens> <body> <Body> <shutter-speed rdf:parseType="Resource"> <min>0.002</min> <max>1.0</max> <units>seconds</units> </shutter-speed> </Body> </body> </SLR> </catalog> </PhotographyStore> ? Need to consult the Camera Ontology!

  17. QuikPhoto.xml - uses familiar terminology <Camera> <lens> <Lens> <size>75-300mm zoom</size> <aperture>4.5-5.6</aperture> </Lens> </lens> <body> <Body> <shutter-speed rdf:parseType="Resource"> <min>0.002</min> <max>1.0</max> <units>seconds</units> </shutter-speed> </Body> </body> </Camera> No need to consult the Camera Ontology.

  18. Lesson Learned • The Camera Application is able to process documents that uses unfamiliar terminology. Interoperates! Community B uses terms Camera, aperture, lens size Community A uses terms SLR, f-stop, focal-length OWL Camera Ontology

  19. Who's Using Ontologies? • Real estate investment agencies are using Ontologies to exchange data with regulatory agencies (Data Consortium - Real Estate Data Standards). • Reuter's Health is using Ontologies to describe the content of articles and sort them into various news feeds (using SNOMED Ontology). • Electric utilities describe their networks using Ontologies for exchange purposes (CIM/XML). • SUN has a large knowledge management initiative called swoRDfish that uses Ontologies.

  20. Related Articles "Why use OWL?" by Roger L. Costello http://www.xfront.com/owl/motivation/sld001.htm "Why use OWL?" by Adam Pease http://www.xfront.com/why-use-owl.html "Using OWL to Avoid Syntactic Rigor Mortis" by Roger L. Costello http://www.xfront.com/avoiding-syntactic-rigor-mortis.html

  21. The OWL Camera Ontology is Online! Here is the URL to a pictorial view of the Camera Ontology: http://www.xfront.com/owl/ontologies/camera/sld001.htm Here is the URL to the camera.owl document: http://www.xfront.com/owl/ontologies/camera/camera.owl Here are the URLs to 7 physical expressions (instance documents): http://www.xfront.com/owl/ontologies/camera/Query1.xml http://www.xfront.com/owl/ontologies/camera/Hunts.xml http://www.xfront.com/owl/ontologies/camera/Query2.xml http://www.xfront.com/owl/ontologies/camera/Hunts2.xml http://www.xfront.com/owl/ontologies/camera/RJs.xml http://www.xfront.com/owl/ontologies/camera/OlympusOutletStore.xml http://www.xfront.com/owl/ontologies/camera/OlympusCorp.xml

  22. The Robber and the Speeder Roger L. Costello David B. Jacobs The MITRE Corporation (The creation of this tutorial was sponsored by DARPA)

  23. An OWL Ontology can be used to answer questions that are implicit in your data 4 How many guns/people are registered in a gun license? 1 <GunLicense> <registeredGun> <Gun> <serial>ABCD</serial> </Gun> </registeredGun> <holder> <Person> <driversLicenseNumber>ZXYZXY</driversLicenseNumber> </Person> </holder> </GunLicense> How many guns can have this serial number? Can this gun be registered in other gun licenses? 2 How many people can have this driver's license number? 3

  24. The OWL Gun License Ontology answers the questions! 4 A gun license registers one gun to one person. <GunLicense> <registeredGun> <Gun> <serial>ABCD</serial> </Gun> </registeredGun> <holder> <Person> <driversLicenseNumber>ZXYZXY</driversLicenseNumber> </Person> </holder> </GunLicense> 1 Only one gun can have this serial number. A gun can be registered in only one gun license. 2 Only one person can have this driver's license number. 3

  25. The Robber and the Speeder • On the next few slides is an example that shows how an OWL Ontology provides the necessary information to link a robber and a speeder. • Thanks to Ian Davis for this example!

  26. Robber drops gun while fleeing! First of all a robbery takes place. The robber drops his gun while fleeing. This report is filed by the investigating officers: <RobberyEvent> <date>...</date> <description>...</description> <evidence> <Gun> <serial>ABCD</serial> </Gun> </evidence> <robber> <Person /> <!-- an unknown person --> </robber> </RobberyEvent>

  27. Speeder stopped Subsequently a car is pulled over for speeding. The traffic officer files this report electronically while issuing a ticket: <SpeedingOffence> <date>...</date> <description>...</description> <speeder> <Person> <name>Fred Blogs</name> <driversLicenseNumber>ZXYZXY</driversLicenseNumber> </Person> </speeder> </SpeedingOffence>

  28. The speeder owns a gun with the same serial number as the robbery gun! At police headquarters (HQ), a computer analyzes each report as it is filed. The computer uses the driver's license information to look up any other records it has about Fred Blogs (the speeder) and discovers this gun license: <GunLicense> <registeredGun> <Gun> <serial>ABCD</serial> </Gun> </registeredGun> <holder> <Person> <driversLicenseNumber>ZXYZXY</driversLicenseNumber> </Person> </holder> </GunLicense>

  29. Case Solved? • Not yet! These questions must be answered before the speeder can be arrested as the robbery suspect: • Can multiple guns have the same serial number? • If so, then just because Fred Blogs owns a gun with the same serial number as the robbery gun does not mean it was his gun that was used in the robbery. • Can multiple people have the same driver's license number? • If so, then the gun license information may be for someone else. • Can a gun be registered in multiple gun licenses? • If so, then the other gun licenses may show the holder of the gun to be someone other than Fred Blogs. • Can a gun license have multiple holders of a registered gun? • If so, then there may be another gun license document (not available at the police HQ) which shows the same registered gun but with a different holder. • The OWL Gun License Ontology provides the information needed to answer these questions! 1 2 3 4

  30. Can multiple guns have the same serial number? This OWL statement tells the computer at police HQ that each gun is uniquely identified by its serial number: <owl:InverseFunctionalProperty rdf:ID="serial"> <rdfs:domain rdf:resource="Gun"/> <rdfs:range rdf:resource="http://www.w3.org/2000/01/rdf-schema#Literal"/> </owl:InverseFunctionalProperty> 1 Only one gun can have this serial number. <Gun> <serial>ABCD</serial> </Gun>

  31. Can multiple people have the same driver's license number? The following OWL statement tells the computer that a driver's license number is unique to a Person: <owl:InverseFunctionalProperty rdf:ID="driversLicenseNumber"> <rdfs:domain rdf:resource="Person"/> <rdfs:range rdf:resource="http://www.w3.org/2000/01/rdf-schema#Literal"/> </owl:InverseFunctionalProperty> 2 Only one person can have this driver's license number. <Person> <driversLicenseNumber>ZXYZXY</driversLicenseNumber> </Person>

  32. Can a gun be registered in multiple gun licenses? The next OWL statement tells the computer that the registeredGun property uniquely identifies a GunLicense, i.e., each gun is associated with only a single GunLicense: <owl:InverseFunctionalProperty rdf:ID="registeredGun"> <rdfs:domain rdf:resource="GunLicense"/> <rdfs:range rdf:resource="Gun"/> </owl:InverseFunctionalProperty> <GunLicense> <registeredGun> <Gun> <serial>ABCD</serial> </Gun> </registeredGun> ... </GunLicense> A gun can be registered in only one gun license. 3

  33. Can a gun license have multiple holders of a registered gun? The police computer uses the following OWL statement to determine that the gun on the license is the same gun used in the robbery. This final statement seals the speeder's fate. It tells the computer that each GunLicense applies to only one gun and one person. So, there is no doubt that the speeder is the person who owns the gun: <owl:Class rdf:ID="GunLicense"> <owl:intersectionOf rdf:parseType="Collection"> <owl:Restriction> <owl:onProperty rdf:resource="#registeredGun"/> <owl:cardinality>1</owl:cardinality> </owl:Restriction> <owl:Restriction> <owl:onProperty rdf:resource="#holder"/> <owl:cardinality>1</owl:cardinality> </owl:Restriction> </owl:intersectionOf> </owl:Class> 4 A gun license registers one gun to one person. <GunLicense> <registeredGun> ... <holder> ... </GunLicense>

  34. Summary • An OWL Ontology provides additional information about your data. • Example: The Gun License Ontology provided the data needed for the police computer to link the Robber and the Speeder! • OWL is intended to be used when processing Web documents. Thus, OWL enables an ad-hoc exploitation of Web documents, i.e., the Semantic Web!