1. OWL
Representing Information Using
the Web Ontology Language 1

2. Section 3 2

3. Section 3 Chapter 11: Encoding an OWL Ontology
Organization of OWL files
Chapter 12: Defining OWL Lite Classes & Properties
Definition of simple classes; pre-defined OWL classes
Chapter 13: Describing OWL Lite Property Characteristics
Global & local property restrictions; inference shortcuts
Chapter 14: Deriving OWL Lite Classes
Class descriptions, subclasses, equivalency, intersections
Chapter 15: Describing Individuals
Unique names assumption; instantiate, relate individuals
Chapter 16: OWL Lite Summary
Summary of OWL Lite constructs 3

4. Chapter 11 4

5. 11 Encoding an OWL Ontology
OWL Ontology encodings
Defined in web documents
Referenced using URI
Developed like software (requirements, design)
Use one of the OWL dialects
Use RDF/XML syntax
Describe classes & properties
OWL knowledge base
Ontology
Instance data
Datatypes
Chapter describes OWL ontology file structure
Header
Body
Footer 5

6. 11.1 OWL Ontology File Structure
Figure shows
Relationship between ontology files, namespaces, & related files
Distribution of ontology files on web servers
Ontologies can extend other ontologies hosted across network
Instances
Reference ontologies
Ontologies
Extend/reuse ontologies
Built on XMLS datatypes 6

7. 11.1 Ontology File Structure cont’d
OWL documents
Best practice: use .owl extension
Include
owl:Ontology element
Class definitions
Property definitions
Typical format
Header
Body
Footer 7

8. 11.2 OWL Header OWL ontology file begins with header
Specifies RDF start tag <rdf>
Includes namespace attributes
Includes ontology element
Contains versioning & imports 8

9. 11.2.1 XML Declaration & RDF Tag
OWL ontologies represented using RDF/XML
Best practice: begin file with
XML declaration including version and encoding
<?xml version="1.0" encoding="UTF-8"?>
<rdf:RDF> start tag containing namespace declarations
<rdf:RDF namespaceDeclarations>
Defined in the next section 9

10. 11.2.2 Namespaces for OWL Ontologies
Namespace declarations
Attributes of <rdf:RDF> start tag
Identify abbreviated references in ontology file
Make file more readable for humans
Can be used in tag & attribute names, not values
Use XML entities for values, if desired
3 types of namespaces
Standard namespace references
Part of OWL standard: XMLS, RDF, RDFS, OWL
Namespaces associated with imported ontologies
Setup shorthand abbreviations to reference URIs
Namespaces identifying ontology being defined
Defined implicitly by document URI, explicitly by “xml:base”, or “xmlns” attribute 10

11. 11.2.2 Ontology Namespaces cont’d
Best practice
Order namespaces from bottom to top
XMLS (for datatypes)
RDF
RDFS
OWL
Reused ontologies
Extended ontologies
Current ontology 11

12. 11.2.2 Ontology Namespaces cont’d
XML Schema Datatypes namespace (xsd prefix)
xmlns:xsd="
RDF namespace (rdf prefix)
xmlns:rdf="
RDFS namespace (rdfs prefix)
xmlns:rdfs="
OWL namespace (owl prefix)
xmlns:owl="
Imported namespace (user-defined prefix)
xmlns:pasta="
Ontology namespace (user-defined prefix)
xmlns=" or
URI of containing document or
Value of xml:base attribute 12

13. 11.2.2 Ontology Namespaces cont’d
xml:base attribute used to expand RDF URIrefs
Best practice: Either
Include xml:base in ontology file or
Use fully-resolved URIs in rdf:about attribute values
Example
<rdf:RDF xmlns:xsd=" xmlns:rdf=" xmlns:rdfs=" xmlns:owl=" xmlns:pasta=" xmlns=" xml:base=" > 13

14. 11.2.3 Ontology Element owl:Ontology element
Built-in class used to instantiate ontologies
Header only, not classes, properties, instances
Optional but recommended
Provides metadata including
Version information
Imports
RDF comments
Should include rdf:about attribute
Empty value ("") means current ontology
Default name: URI of document, unless xml:base specified 14

15. 11.2.3 Ontology Element cont’d
owl:Ontology element
Recommended practices
Give name using rdfs:label property
Comment using rdfs:comment property
Syntax
<owl:Ontology rdf:about="optionalOntologyName"> </owl:Ontology>
Example
<owl:Ontology rdf:about=""> <rdfs:label>Restaurant Menu</rdfs:label> <rdfs:comment>Describes basic concepts representing a restaurant’s menu</rdfs:comment> </owl:Ontology> 15

16. 11.2.3.1 Versioning Information
OWL provides explicit versioning info including
Ontology-level versioning
Compatibility statements about previous versions
Deprecation declarations
Classes & properties for backward compatibility 16

17. 11.2.3.1.1 Version Information owl:versionInfo property Syntax Example
String representing ontology’s version
Can use RCS, CVS, Subversion keywords (see example)
Documentation comment; no logical meaning
Normally used for ontologies but can be applied to any owl:Thing
Best practice: use owl:versionInfo in each OWL document
May eventually evolve into parseable “Dublin Core” items
Domain: Instance of owl:Thing, Range: Instance of rdfs:Literal
Syntax
<owl:versionInfo>versionText</owl:versionInfo>
Example
<owl:Ontology> <owl:versionInfo>$Id: restaurantMenu-ont.owl,v /08/30 12:34:56 llacy Exp$</owl:VersionInfo> </owl:Ontology> 17

18. 11.2.3.1.1.1 Indicating Earlier Version
owl:priorVersion property
Relates newer version to previous version
Tracks ontology version history
Domain & Range: Instance of owl:Ontology
Syntax
<owl:priorVersion rdf:resource="priorOntURI"/>
Example
<owl:Ontology rdf:about=""> <owl:priorVersion rdf:resource=" </owl:Ontology> 18

19. 11.2.3.1.1.2 Backward-Compatibility
owl:backwardCompatibleWith property
Explicitly states that all constructs in this version have the same meaning as in the prior version
Subproperty of owl:priorVersion
If not explicitly stated, incompatibility assumed
Domain & Range: Instance of owl:Ontology
Syntax
<owl:backwardCompatibleWith rdf:resource="olderOntURI"/>
Example
<owl:Ontology rdf:about=""> <owl:backwardCompatibleWith rdf:resource="&kor;Menu ont"/> <rdfs:comment>added new menu items since 06/22/04</rdfs:comment> </owl:Ontology> 19

20. 11.2.3.1.1.3 Incompatible Ontologies
owl:incompatibleWith property
Identifies prior versions that this ontology supersedes and is inconsistent with
Subproperty of owl:PriorVersion
Best practice: include incompatibility comments
Domain & Range: Instance of owl:Ontology
Syntax
<owl:incompatibleWith rdf:resource="olderOntURI"/>
Example
<owl:Ontology rdf:about=""> <owl:incompatibleWith rdf:resource="&kor;Menu ont"/> <rdfs:comment>added new menu items</rdfs:comment> </owl:Ontology> 20

21. 11.2.3.1.1.4 Deprecating Classes owl:DeprecatedClass class Syntax
Identifies classes no longer supported in future versions
Supports short-term compatibility
Existing ontologies should upgrade to new concepts as soon as possible
Signals long-term incompatibility
New ontologies should not reference deprecated classes
No semantics; treated as comment by parser
Best practice: provide comment indicating replacement class
Syntax
<owl:DeprecatedClass rdf:about="OldClassName">
Example
<owl:DeprecatedClass rdf:about="#Pie"> <rdfs:comment>Use DessertPie instead</rdfs:comment> </owl:DeprecatedClass> 21

22. 11.2.3.1.1.5 Deprecating Properties
owl:DeprecatedProperty class
Identifies properties no longer supported in future versions
Same concepts as owl:DeprecatedClass
Best practice: provide comment indicating replacement property
Syntax
<owl:DeprecatedProperty rdf:about="oldPropertyName">
Example
<owl:DeprecatedProperty rdf:about="#cost"> <rdfs:comment>Use menuPrice instead</rdfs:comment> </owl:DeprecatedProperty> 22

23. 11.2.3.1.1.6 Versioning Summary Construct Purpose owl:versionInfo
Provides version information
owl:priorVersion
Identifies earlier version of subject ontology
owl:backwardCompatibleWith
Identifies earlier version compatible with
subject ontology
owl:incompatibleWith
Identifies earlier version incompatible with
owl:DeprecatedClass
Identifies class that should no longer be used
owl:DeprecatedProperty
Identifies property that should no longer be used
Versioning constructs
Documentation only
Do not provide additional semantics
Not intended for use by inferencing engines 23

24. 11.2.3.2 Importing Ontologies owl:imports property
Allows an ontology to reference and extend another ontology
Supports incremental & distributed ontologies
Similar to “include”/“import” in programming languages
Introduces dependencies
Made in the ontology element of importing ontology
Domain & Range: Instance of owl:Ontology
OWL ontology always implicitly imported
Syntax
<owl:imports rdf:resource="URIofImportedOntology"/>
Example
<owl:imports rdf:resource=" 24

25. 11.2.3.2 Namespace vs. Imports cont’d
Namespace declarations
Create prefix abbreviations for identifiers
owl:imports properties
Include all constructs from ontology referenced in URI
Use namespace declaration to create shortened names to reference ontology constructs
Example
<rdf:RDF xmlns:pasta="
<owl:Ontology about=""> <owl:imports rdf:resource=" </owl:Ontology> 25

26. 11.2.3.2 Imports Rules cont’d Multiple imports permitted
owl:imports are transitive
A imports B
B imports C
Therefore A imports C
No effect if ontology imports itself (prevents cycles)
If A imports B and B imports A, A and B are equivalent
If imported ontology not accessible at specified URI during runtime, it may prevent use of importing ontology 26

27. 11.2.3.3 Ontology Element Summary
owl:Ontology element provides metadata
Version information (owl:versionInfo & related)
Name (rdfs:label property)
Descriptive comments (rdfs:comment property)
Imported ontologies (owl:imports property)
Example complete ontology element
<owl:Ontology rdf:about=""> <owl:versionInfo>v /10/24</owl:versionInfo> <rdfs:comment>Restaurant Menu ontology</rdfs:comment> <owl:imports rdf:resource="&rest;2004/08/food-ont"/> <owl:priorVersion rdf:resource="&rest;2004/07/Menu-ont"/> <owl:incompatibleWith rdf:resource="&rest;2004/06/Menu-ont"/> <owl:backwardCompatibleWith rdf:resource="&rest;2004/07/Menu- ont"/> <owl:Ontology> 27

28. 11.2.4 OWL Header Summary OWL file header contains
RDF tag and namespace properties
owl:Ontology element 28

29. 11.3-4 OWL File Body & Footer OWL file body
Contains class & property definitions
Classes derive from owl:Class; share similar properties
Values are XMLS datatypes or object instances
Properties define relationships between classes & values
Order is not important
Forward references are permitted
Co-occurring statements assumed to be conjunctive (AND)
“Open World Assumption”
Anything that is not explicitly stated cannot be assumed to be either true or false. Statements can only be added, not deleted.
Limits inferencing and deductive power
OWL files end with </rdf:RDF> end tag 29

30. 11.5 OWL Encoding Summary
OWL ontologies specified through statements in ontology files
Ontology files contain
Header contains
Namespaces
Versioning Information
Import Statements
Body contains statements about
Classes
Properties
Relationships
Footer (rdf:RDF end tag) 30

31. Chapter 12 31

32. 12 Defining Basic Classes & Properties
OWL Lite classes
Based on owl:Class, a richer subclass of rdfs:Class
2 basic class types
Simple named classes
Predefined classes
owl:Thing, owl:Nothing
OWL Lite properties
Based on rdf:Property
4 basic property types
owl:DatatypeProperty, owl:ObjectProperty, owl:AnnotationProperty, owl:OntologyProperty 32

33. 12.1 Defining a Simple Named Class
Simple named classes
Defined with owl:Class element & rdf:ID attribute
Does nothing but declare a name (URI)
Within same file, often referenced by fragment (#classname)
All statements about a class apply to its individuals
Best practices:
Name using UpperCamelCase
Use rdfs:label and rdfs:comment to document
Syntax
<owl:Class rdf:ID="className"/>
Example
<owl:Class rdf:ID="KeyLimePie"> <rdfs:label>Key Lime Pie</rdfs:label> <rdfs:comment>Custard pie made with Key lime juice</rdfs:comment> </owl:Class> 33

34. 12.2 Predefined OWL Classes
OWL defines two “extreme” classes
owl:Thing
Used in statements that apply to all instances
owl:Nothing
Used in statements that apply to no instances 34

35. 12.2.1 Thing Class owl:Thing class Most general class in OWL
Root class for all classes
Even rdf:Resource, root class of RDF
Every individual is a member of owl:Thing
Every class is a subclass of owl:Thing
Equal to the union of any class and its complement
Set equivalent of “universe”
Can be used to make global assertions 35

36. 12.2.2 Nothing class owl:Nothing class Subclass of all classes
Empty class
No member individuals
Set equivalent of “null set” 36

37. 12.3 Describing OWL Lite Properties
Are binary relations from one individual (domain) to another individual or a value (range)
Enable specification of facts (attribute/value pairs)
Four disjoint property types in OWL
Datatype properties relate objects to datatype values
Object properties relate objects to other objects
Annotation properties describe objects
Ontology properties relate ontologies to other ontologies 37

38. 12.3.1 Datatype Properties owl:DatatypeProperty class Syntax
Identifies a property whose value is a member of a datatype (typed or untyped literals)
Strings or simple XMLS datatypes
Reasoners use them to interpret a statement’s datatype value
Syntax
<owl:DatatypeProperty rdf:ID="propertyName"/>
Example (specification)
<owl:DatatypeProperty rdf:ID="restCloseTime"> <rdfs:domain rdf:resource="#Restaurant"/> <rdfs:range rdf:resource="&xsd;time"/> </owl:DatatypeProperty>
Example (use)
<rest:Restaurant rdf:ID="JoesPizza"> <restCloseTime rdf:datatype="&xsd;time">21:00:00+01:00</restCloseTime> </rest:Restaurant> 38

39. 12.3.2 Object Properties owl:ObjectProperty class Syntax
Identifies property whose value is reference to another individual
Value is a resource
Points Reasoner to resource containing desired value
“What is the name of the owner of Knight Owl Restaurant?” (see below)
Syntax
<owl:ObjectProperty rdf:ID="propertyName"/>
Example (specification)
<owl:ObjectProperty rdf:ID="restOwnedBy"/>
Example (use)
<rest:Person rdf:ID="person123"> <personName>Jason Relles</personName> </rest:Person>
<rest:Restaurant rdf:ID="KnightOwlRestaurant"> <ownedBy rdf:resource="#person123"/> </rest:Restaurant> 39

40. 12.3.3 Annotation Properties
owl:AnnotationProperty class
Identifies property that describes a construct
Superclass of rdfs:label, rdfs:comment, rdfs:seeAlso, rdfs:isDefinedBy, owl:versionInfo
Domain: named class, property, individual, or ontology
Range: individual, data literal, URIref
Syntax
<owl:AnnotationProperty rdf:about="uriRef"/>
Example
<owl:AnnotationProperty rdf:about="&rest;reviewer"/> 40

41. 12.3.4 Ontology Properties owl:OntologyProperty class
Relates two owl:Ontology instances
Superclass of owl:imports, owl:priorVersion, owl:backwardCompatibleWith, owl:incompatibleWith
Not often used in practice 41

42. 12.4 Classes & Properties Summary
Basic classes are defined using owl:Class
owl:Thing is a universal root class & contains everything
owl:Nothing is a universal subclass & contains nothing
Datatype properties relate objects to literal values
Object properties relate objects to other objects
Annotation properties provide additional information
Ontology properties relate ontologies to other ontologies 42