1 Dr Alexiei Dingli Introduction to Web Science Modelling Knowledge

2 Acquire Model Reuse Retrieve Publish Maintain Six challenges of the Knowledge Life Cycle

3 Shared ontologies help to exchange data and meaning between web-based services The Semantic Web (Image by Jim Hendler)

4 Wine Example Scenario Tell me what wines I should buy to serve with each course of the following menu. Wine Agent Grocery Agent Books Agent I recommend Chardonney or DryRiesling

5 Provide shared data structures to exchange information between agents Can be explicitly used as annotations in web sites Can be used for knowledge-based services using other web resources Can help to structure knowledge to build domain models (for other purposes) Ontologies in the Semantic Web

6 Web Ontology Language Official W3C Standard since Feb 2004 Based on predecessors (DAML+OIL) A Web Language: Based on RDF(S) An Ontology Language: Based on logic OWL

7 What’s inside an OWL ontology –Classes + class-hierarchy –Properties (Slots) / values –Relations between classes (inheritance, disjoints, equivalents) –Restrictions on properties (type, cardinality) –Characteristics of properties (transitive, …) –Instances Reasoning tasks: classification, consistency checking OWL Ontologies

8 At least two different user groups –OWL used as data exchange language (define interfaces of services and agents) –OWL used for terminologies or knowledge models OWL DL is the subset of OWL (Full) that is optimized for reasoning and knowledge modeling OWL Use Cases

9 Tutorial Scenario Semantic Web for Tourism/Traveling Goal: Find matching holiday destinations for a customer I am looking for a comfortable destination with beach access Tourism Web

10 A search problem: Match customer’s expectations with potential destinations Required: Web Service that exploits formal information about the available destinations –Accomodation (Hotels, B&B, Camping,...) –Activities (Sightseeing, Sports,...) Scenario Architecture

11 Open World: –New hotels are being added –New activities are offered Providers publish their services dynamically Standard format / grounding is needed → Tourism Ontology Tourism Semantic Web

12 Tourism Semantic Web OWL Metadata (Individuals) OWL Metadata (Individuals) OWL Metadata (Individuals) OWL Metadata (Individuals) Tourism Ontology Web Services Destination AccomodationActivity

13 OWL (in Protégé) Instances (e.g., “Golden Sands”) Properties – ObjectProperties (references) – DatatypeProperties (simple values) Classes (e.g., “Hotel”)

14 Represent objects in the domain Specific things Two names could represent the same “real-world” instance Instances Ghajn Tuffieha Golden Bay Malta

15 Link two individuals together Relationships (0..n, n..m) ObjectProperties Malta Golden Bay hasPart Golden Sands hasAccomodation

16 Represent bidirectional relationships Adding a value to one property also adds a value to the inverse property Inverse Properties Malta Golden Bay hasPart isPartOf

17 If A is related to B and B is related to C then A is also related to C Often used for part-of relationships Transitive Properties Malta Golden Bay hasPart The Maltese Islands hasPart hasPart (derived)

18 Link individuals to primitive values (integers, floats, strings, booleans etc) DatatypeProperties Valletta hasSize = 6,000 isCapital = true rdfs:comment = “Don’t miss the Cathedral”

19 Sets of individuals with common characteristics Individuals are instances of at least one class Classes City Valletta Beach Sliema Golden Bay Paradise Bay

20 Property characteristics –Domain: “left side of relation” (Destination) –Range: “right side” (Accomodation) Range and Domain Malta Golden Sands Vivaldi hasAccomodation Destination Accomodation hasAccomodation

21 Instances can only take values of properties that have matching domain –“Only Destinations can have Accomodations” Domain can contain multiple classes Domains

22 Classes can be organized in a hierarchy Direct instances of subclass are also (indirect) instances of superclasses Superclass Relationships Harbor Area Sliema Valletta Gzira

23 Classes can overlap arbitrarily Class Relationships City Sliema Valletta Qawra RetireeDestination

24 All classes could potentially overlap In many cases we want to make sure they don’t share instances Class Disjointness Sydney UrbanAreaRuralArea Valletta Qawra St Paul’s disjointWith City Destination

25 (Create a new OWL project)

26 (Create simple classes)

27 (Create class hierarchy and set disjoints)

28 (Create Contact class with datatype properties)

29 (Edit details of datatype properties)

30 (Create an object property hasContact)

31 (Create an object property with inverse)

32 (Create the remaining classes and properties)

33 Tool 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? Reasoning with Classes

34 Define a condition for property values – allValuesFrom – someValuesFrom – hasValue – minCardinality – maxCardinality – cardinality Restrictions (Overview)

35 Meaning: The property must have at least/at most/exactly x values is the shortcut for and Example: A FamilyDestination is a Destination that has at least one Accomodation and at least 2 Activities Cardinality Restrictions

36 Meaning: 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 allValuesFrom Restrictions

37 Meaning: 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 someValuesFrom Restrictions

38 Meaning: 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 hasValue Restrictions

39 Consist of exactly the listed individuals Enumerated Classes OneStarRating TwoStarRating ThreeStarRating BudgetAccomodation

40 Define 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) Logical Class Definitions

41 The class of individuals that belong to class A or class B (or both) Example: Adventure or Sports activities unionOf AdventureSports

42 The 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 intersectionOf BudgetAccomodation Hotel

43 When 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 accomodation with 3 stars Implicit intersectionOf AccomodationWith3Stars Hotel LuxuryHotel

44 The class of all individuals that do not belong to a certain class Example: A quiet destination is a destination that is not a family destination complementOf Destination FamilyDestination QuietDestination (grayed)

45 A RuralArea is a Destination A Campground is BudgetAccomodation Hiking is a Sport Therefore: Every NationalPark is a Backpackers-Destiantion Classification NationalPark BackpackersDestination (Other BackpackerDestinations)

46 Input: Asserted class definitions Output: Inferred subclass relationships Classification (2)

47 (Create an enumerated class out of individuals)

48 (Create a hasValue restriction)

49 (Create a hasValue restriction)

50 (Classify Campground)

51 (Add restrictions to City and Capital)

52 (Create defined class BackpackersDestination)

53 (Create defined class FamilyDestination)

54 (Create defined class QuietDestination)

55 (Create defined class RetireeDestination)

56 (Classification)

57 (Consistency Checking)

58 Visualization with OWLViz

59 OWL Wizards

60 Ontology has been developed Published on a dedicated web address Ontology provides standard terminology Other ontologies can extend it Users can instantiate the ontology to provide instances –specific hotels –specific activities Putting it All Together

61 Tourism Semantic Web OWL Metadata (Individuals) Tourism Ontology Web Services Destination AccomodationActivity

62 The ontology should not contain all the possible information about the domain: you do not need to specialize (or generalize) more than you need for your application (at most one extra level each way) Warning!!

63 1.Determine the domain and scope of the ontology 2.Defining classes in the ontology 3.Arranging the classes in a taxonomic (subclass–superclass) hierarchy 4.Defining slots and describing allowed values for these slots 5.Creating instances Hint: Steps to create an ontology …

64 Divide class into 2 Create an ontology representing special occasions … –E.g. wedding, birthday, Christmas, etc Wins the group that creates the most complete ontology Exercise