Post on 03-Feb-2016
Embed Size (px)
DESCRIPTIONSemantic Web. Andrejs Lesovskis. Semantic Web layers. Ontology spectrum (1). Strong semantics. Modal Logic. First Order Logic. Logical theory. Is Disjoint Subclass of with transitivity property. Description Logic. DAML+OIL, OWL. From less to more expressive. UML. Conceptual model. - PowerPoint PPT Presentation
Semantic WebAndrejs Lesovskis
Semantic Web layers
Ontology spectrum (1)Weak semanticsStrong semanticsIs Disjoint Subclass of with transitivity propertyModal LogicLogical theoryThesaurusHas narrower meaning thanTaxonomyIs sublassification ofConceptual modelIs subclass ofDB Schemas, XML SchemaUMLFirst Order LogicRelationalModel, XMLERExtended ERDescription LogicDAML+OIL, OWLRDF/SXTMSyntactic InteroperabilityStructural InteroperabilitySemantic InteroperabilityFrom less to more expressive
Ontology spectrum (2)Weak semanticsStrong semanticsIs Disjoint Subclass of with transitivity propertyModal LogicLogical theoryThesaurusHas narrower meaning thanTaxonomyIs sublassification ofConceptual modelIs subclass ofDB Schemas, XML SchemaUMLFirst Order LogicRelationalModel, XMLERExtended ERDescription LogicDAML+OIL, OWLRDF/SXTMSyntactic InteroperabilityStructural InteroperabilitySemantic InteroperabilityFrom less to more expressiveProblem: Very GeneralSemantic Expressivity: Very HighProblem: Local Semantic Expressivity: LowProblem: GeneralSemantic Expressivity: MediumProblem: GeneralSemantic Expressivity: High
Open and Closed World AssumptionsThe Closed World Assumption (CWA) is the assumption that what is not known to be true must be false.Imagine, we have the following statement "Peteris is a citizen of Latvia." and we are asked "Is Peteris a citizen of Lithuania? ", under the CWA, the answer is no.
Open and Closed World AssumptionsThe Open World Assumption (OWA) is the opposite. In other words, it is the assumption that what is not known to be true is simply unknown.Under the OWA, the answer to the question about Peteris is "I dont know".The Web is a system with incomplete information. Absence of information on the Web means that the information has not been made explicit. Therefore, Semantic Web uses the Open World Assumption.
Protg OWL PluginExtension of Protg for handling OWL ontologies.Project started in April 2003.Features:Loading and saving OWL files and databases;Graphical editors for class expressions;Access to description logics reasoners;Powerful platform for hooking in custom-tailored components.
OWL Plugin ArchitectureProtg API(Classes, properties,individuals, etc.)Protg GUI(Tabs, Widgets, Menus)DBStorageProtg Core System
Tutorial ScenarioSemantic Web for Tourism/Traveling domainGoal: Find matching holiday destinations for a customerI am looking for a comfortable destination with beach accessTourism Web
Scenario descriptionA search problem: Match customers expectations with potential destinationsRequired: Web Service that exploits formal information about the available destinations:Accomodation (Hotels, B&B, Camping, ...),Activities (Sightseeing, Sports, ...),etc.
Semantic Web for tourism domainOpen World:New hotels are being added,New activities are offered.Providers publish their services dynamically.Standard format / grounding is needed Tourism Ontology.
Tourism Semantic WebOWLMetadata(Individuals)Tourism OntologyWeb ServicesDestinationAccomodationActivityOWLMetadata(Individuals)OWLMetadata(Individuals)OWLMetadata(Individuals)
IndividualsRepresent objects in the domain.Specific things.Two names (synonyms) could represent the same real-world individual.
ObjectPropertiesLink two individuals together using particular relationships (0..n, n..m).
Inverse PropertiesRepresent bidirectional relationships.Adding a value to one property also adds a value to the inverse property.
DatatypePropertiesLink individuals to primitive values (integers, floats, strings, booleans, etc).Often: AnnotationProperties without formal meaning.hasSize = 4,500,000isCapital = truerdfs:comment = Dont miss the opera house
ClassesSets of individuals with common characteristics.Individuals are instances of at least one class (OWL supports multiple inheritance).
Range and DomainProperty characteristicsDomain: left side of relation (Destination);Range: right side (Accomodation).
DomainsIndividuals can only take values of properties that have matching domain:Only Destinations can have Accomodations.Domain can contain multiple classes.Domain can be undefined: Property can be used everywhere.
Superclass RelationshipsClasses can be organized in a hierarchy.Direct instances of subclass are also (indirect) instances of superclasses.
Class RelationshipsClasses can overlap arbitrarily.
Class DisjointnessAll classes could potentially overlap.In many cases we want to make sure they dont share instances.disjointWith
(Create a new OWL project)
(Create simple classes)
(Create class hierarchy and set disjoints)
(Create Contact class with datatype properties)
(Edit details of datatype properties)
(Create an object property hasContact)
(Create an object property with inverse)
(Create the remaining classes and properties)
Class DescriptionsClasses can be described by their logical characteristics.Descriptions are anonymous classes.
Class DescriptionsDefine the meaning of classes.Anonymous class expressions are used:All national parks have campgrounds.,A backpackers destination is a destination that has budget accomodation and offers sports or adventure activities.Expressions mostly restrict property values (OWL Restrictions).
Class Descriptions: Why?Based on OWLs Description Logic support.Formalize intentions and modeling decisions (comparable to test cases).Make sure that individuals fulfill conditions.Tool-supported reasoning.
Reasoning with ClassesTool support for three types of reasoning exists:Consistency checking: Can a class have any instances?Classification: Is A a subclass of B?Instance classification: Which classes does an individual belong to?
Restrictions (Overview)Define a condition for property values allValuesFrom someValuesFrom hasValue minCardinality maxCardinality cardinalityAn anonymous class consisting of all individuals that fulfill the condition
Cardinality RestrictionsMeaning: The property must have at least/at most/exactly x values is the shortcut for andExample: A FamilyDestination is a Destination that has at least one Accomodation and at least 2 Activities
allValuesFrom RestrictionsMeaning: All values of the property must be of a certain type.Warning: Also individuals with no values fulfill this condition (trivial satisfaction).Example: Hiking is a Sport that is only possible in NationalParks.
someValuesFrom RestrictionsMeaning: At least one value of the property must be of a certain type.Others may exist as well.Example: A NationalPark is a RuralArea that has at least one Campground and offers at least one Hiking opportunity.
hasValue RestrictionsMeaning: At least one of the values of the property is a certain value.Similar to someValuesFrom but with Individuals and primitive values.Example: A PartOfSydney is a Destination where one of the values of the isPartOf property is Sydney.
Enumerated ClassesConsist of exactly the listed individuals.
Logical Class DefinitionsDefine classes out of other classes unionOf (or) intersectionOf (and) complementOf (not)Allow arbitrary nesting of class descriptions (A and (B or C) and not D)
unionOfThe class of individuals that belong to class A or class B (or both)Example: Adventure or Sports activities
intersectionOfThe class of individuals that belong to both class A and class B.Example: A BudgetHotelDestination is a destination with accomodation that is a budget accomodation and a hotel.
Implicit intersectionOfWhen a class is defined by more than one class description, then it consists of the intersection of the descriptions.Example: A luxury hotel is a hotel that is also an accommodation with 3 stars.
complementOfThe class of all individuals that do not belong to a certain classExample: A quiet destination is a destination that is not a family destination
Class ConditionsNecessary Conditions: (Primitive / partial classes) If we know that something is a X, then it must fulfill the conditions... Necessary & Sufficient Conditions: (Defined / complete classes) If something fulfills the conditions..., then it is an X.
Class Conditions (2)(not everything that fulfills these conditions is a NationalPark)(everything that fulfills these conditions is a QuietDestination)
ClassificationA RuralArea is a DestinationA Campground is BudgetAccomodationHiking is a SportTherefore: Every NationalPark is a Backpackers-Destiantion(Other BackpackerDestinations)
Classification (2)Input: Asserted class definitions.Output: Inferred subclass relationships.
(Create an enumerated class out of individuals)
(Create a hasValue restriction)
(Create a hasValue restriction)
(Create a defined class)
(Add restrictions to City and Capital)
(Create defined class BackpackersDestination)
(Create defined class FamilyDestination)
(Create defined class QuietDestination)
(Create defined class RetireeDestination)
Visualization with OWLViz
Putting it All TogetherOntology has been developed;Published on a dedicated web address;Ontology provides standard terminology;Other ontologies can e