1. 1 Berendt: Knowledge and the Web, 1st semester 2015/2016, http://http://people.cs.kuleuven.be/~bettina.berendt/teaching/ 1 Knowledge and the Web – The Semantic Web Bettina Berendt KU Leuven, Department of Computer Science http://people.cs.kuleuven.be/~bettina.berendt/teaching/ Last update: 14 October 2015

2. 2 Berendt: Knowledge and the Web, 1st semester 2015/2016, http://http://people.cs.kuleuven.be/~bettina.berendt/teaching/ 2 Outlook The Semantic Web: Motivation and overview Semantics, concepts and ontologies Very brief recap of XML (& why it’s not semantic) RDF and RDFS Linked (Open) Data (LOD)

3. 3 Berendt: Knowledge and the Web, 1st semester 2015/2016, http://http://people.cs.kuleuven.be/~bettina.berendt/teaching/ 3 The original vision The entertainment system was belting out the Beatles' "We Can Work It Out" when the phone rang. When Pete answered, his phone turned the sound down by sending a message to all the other local devices that had a volume control. His sister, Lucy, was on the line from the doctor's office: "Mom needs to see a specialist and then has to have a series of physical therapy sessions. Biweekly or something. I'm going to have my agent set up the appointments." Pete immediately agreed to share the chauffeuring. At the doctor's office, Lucy instructed her Semantic Web agent through her handheld Web browser. The agent promptly retrieved information about Mom's prescribed treatment from the doctor's agent, looked up several lists of providers, and checked for the ones in-plan for Mom's insurance within a 20-mile radius of her home and with a rating of excellent or very good on trusted rating services. It then began trying to find a match between available appointment times (supplied by the agents of individual providers through their Web sites) and Pete's and Lucy's busy schedules. (The emphasized keywords indicate terms whose semantics, or meaning, were defined for the agent through the Semantic Web.) Tim Berners-Lee, James Hendler and Ora Lassila (2001). The Semantic Web. A new form of Web content that is meaningful to computers will unleash a revolution of new possibilities. Scientific American. http://www.sciam.com/article.cfm?articleID=00048144-10D2-1C70-84A9809EC588EF21 available at http://www.cs.umd.edu/~golbeck/LBSC690/SemanticWeb.htmlhttp://www.sciam.com/article.cfm?articleID=00048144-10D2-1C70-84A9809EC588EF21http://www.cs.umd.edu/~golbeck/LBSC690/SemanticWeb.html

4. 4 Berendt: Knowledge and the Web, 1st semester 2015/2016, http://http://people.cs.kuleuven.be/~bettina.berendt/teaching/ 4 The Semantic Web: overview n The semantic web is an evolving extension of the World Wide Web in which web content can be expressed not only in natural language, but also in a format that can be read and used by software agents, thus permitting them to find, share and integrate information more easily.World Wide Web web contentnatural languagereadsoftware agentsintegrate n It derives from W3C director Sir Tim Berners-Lee's vision of the Web as a universal medium for data, information, and knowledge exchange.W3CSir Tim Berners-Leedatainformationknowledge n At its core, the semantic web comprises a philosophy, a set of design principles, collaborative working groups, and a variety of enabling technologies.working groups n Some elements of the semantic web are expressed as prospective future possibilities that have yet to be implemented or realized. n Other elements of the semantic web are expressed in formal specifications. n Some of these include Resource Description Framework (RDF), a variety of data interchange formats (e.g. RDF/XML, N3, Turtle, N-Triples), and notations such as RDF Schema (RDFS) and the Web Ontology Language (OWL), all of which are intended to provide a formal description of concepts, terms, and relationships within a given knowledge domain.Resource Description FrameworkRDF/XMLN3TurtleN-TriplesRDF SchemaWeb Ontology Languageformal descriptionconcepts termsrelationshipsknowledge domain

5. 5 Berendt: Knowledge and the Web, 1st semester 2015/2016, http://http://people.cs.kuleuven.be/~bettina.berendt/teaching/ 5 The Semantic Web layer cake (T. Berners-Lee talk at XML 2000) RDF: W3C Rec. 2004 OWL: W3C Rec. 2004 OWL2: W3C Rec. 2009

6. 6 Berendt: Knowledge and the Web, 1st semester 2015/2016, http://http://people.cs.kuleuven.be/~bettina.berendt/teaching/ 6 5 ★ Open Data: Formats example http://5stardata.info/en/

7. 7 Berendt: Knowledge and the Web, 1st semester 2015/2016, http://http://people.cs.kuleuven.be/~bettina.berendt/teaching/ 7 5 ★ Open Data (Berners-Lee, 2006) http://www.w3.org/DesignIssues/LinkedData.html, http://5stardata.info/en/

8. 8 Berendt: Knowledge and the Web, 1st semester 2015/2016, http://http://people.cs.kuleuven.be/~bettina.berendt/teaching/ 8 Does it even exist? Example “Marie Curie“ https://en.wikipedia.org/wiki/Marie_Curie http://dbpedia.org/page/Marie_Curie This contains many links to DBPedia itself (e.g. dbo:... ), but also to other LOD datasets – for example, the resources prefixed by yago: (see http://www.mpi-inf.mpg.de/departments/databases- and-information-systems/research/yago-naga/yago//)http://www.mpi-inf.mpg.de/departments/databases- and-information-systems/research/yago-naga/yago// freebase: (see https://www.freebase.com/)https://www.freebase.com/ foaf: (see http://www.foaf-project.org/)http://www.foaf-project.org/

9. 9 Berendt: Knowledge and the Web, 1st semester 2015/2016, http://http://people.cs.kuleuven.be/~bettina.berendt/teaching/ 9 Are there RDF data in a Website? E.g. https://addons.mozilla.org/en-US/firefox/addon/semantic-radar/

10. 10 Berendt: Knowledge and the Web, 1st semester 2015/2016, http://http://people.cs.kuleuven.be/~bettina.berendt/teaching/ 10 The potential http://linkedu.eu/dedalo/demo/

11. 11 Berendt: Knowledge and the Web, 1st semester 2015/2016, http://http://people.cs.kuleuven.be/~bettina.berendt/teaching/ 11 The potential (example of the use of traversing LOD) http://linkedu.eu/dedalo/demo/

12. 12 Berendt: Knowledge and the Web, 1st semester 2015/2016, http://http://people.cs.kuleuven.be/~bettina.berendt/teaching/ 12 The potential (contd.)... And of course our invited speakers next week and the week after!

13. 13 Berendt: Knowledge and the Web, 1st semester 2015/2016, http://http://people.cs.kuleuven.be/~bettina.berendt/teaching/ 13 BTW: Semantic non-interoperability has real consequences...

14. 14 Berendt: Knowledge and the Web, 1st semester 2015/2016, http://http://people.cs.kuleuven.be/~bettina.berendt/teaching/ 14... A spatial example (as recently as 2006)

15. 15 Berendt: Knowledge and the Web, 1st semester 2015/2016, http://http://people.cs.kuleuven.be/~bettina.berendt/teaching/ 15 Outlook The Semantic Web: Motivation and overview Semantics, concepts and ontologies Very brief recap of XML (& why it’s not semantic) RDF and RDFS Linked (Open) Data (LOD)

16. 16 Berendt: Knowledge and the Web, 1st semester 2015/2016, http://http://people.cs.kuleuven.be/~bettina.berendt/teaching/ 16 What is „semantic“ anyway? Semantics is the study of meaning. It focuses on the relation between signifiers, like words, phrases, signs, and symbols, and what they stand for; their denotation. Linguistic semantics is the study of meaning that is used for understanding human expression through language. Other forms of semantics include the semantics of programming languages, formal logics, and semiotics. In computer science, the term semantics refers to the meaning of languages, as opposed to their form (syntax). In logic, formal semantics OR logical semantics,[1][2][3] is the study of the semantics, or interpretations, of formal and (idealizations of) natural languages usually trying to capture the pre-theoretic notion of entailment.

17. 17 Berendt: Knowledge and the Web, 1st semester 2015/2016, http://http://people.cs.kuleuven.be/~bettina.berendt/teaching/ 17 What is „semantic“ in the sense of the Semantic Web? To use web content, machines need to know what to do when they encounter it, which, in turn, requires the machine to know what the content means (that is, its semantics). The challenge of developing the semantic web is how to put this knowledge into the machine. The manner in which it is done is at the heart of the confusion about the semantic web. The goal of this article is to clear up some of this confusion. Uschold, „“Where Are the Semantics in the Semantic Web?”, AI Magazine 2003, https://www.aaai.org/ojs/index.php/aimagazine/article/viewFile/17 16/1614

18. 18 Berendt: Knowledge and the Web, 1st semester 2015/2016, http://http://people.cs.kuleuven.be/~bettina.berendt/teaching/ 18 Search for „FUEL PUMP“  why information about pistons may be relevant

19. 19 Berendt: Knowledge and the Web, 1st semester 2015/2016, http://http://people.cs.kuleuven.be/~bettina.berendt/teaching/ 19 Doesn‘t Google do this (without knowledge structures in the background)?

20. 20 Berendt: Knowledge and the Web, 1st semester 2015/2016, http://http://people.cs.kuleuven.be/~bettina.berendt/teaching/ 20

21. 21 Berendt: Knowledge and the Web, 1st semester 2015/2016, http://http://people.cs.kuleuven.be/~bettina.berendt/teaching/ 21 Concepts A concept is an abstraction or generalization from experience or the result of a transformation of existing concepts. The concept reifies all of its actual or potential instances whether these are things in the real world or other ideas.ideas

22. 22 Berendt: Knowledge and the Web, 1st semester 2015/2016, http://http://people.cs.kuleuven.be/~bettina.berendt/teaching/ 22 Ontologies and concepts n An ontology is a conceptual model. n An Ontology is the collection of semantic definitions for a domain. n Example: an Aircraft Ontology is the set of semantic definitions for the Aircraft domain, e.g., Predator is a subClassOf Aircraft. sensorID is a FunctionalProperty. Platform is an equivalentClass to Aircraft. n Predator, Aircraft etc. are concepts.

23. 23 Berendt: Knowledge and the Web, 1st semester 2015/2016, http://http://people.cs.kuleuven.be/~bettina.berendt/teaching/ 23 Basic idea of conceptual modelling (not only in SW): The semiotic triangle (to be deconstructed later...)

24. 24 Berendt: Knowledge and the Web, 1st semester 2015/2016, http://http://people.cs.kuleuven.be/~bettina.berendt/teaching/ 24 What is an ontology? (A commonly accepted informal definition and one formal definition) An ontology is „an explicit specification of a shared conceptualisation.“ (Gruber, 1993) (Stumme, Hotho & Berendt, Semantic Web Journal 2006))

25. 25 Berendt: Knowledge and the Web, 1st semester 2015/2016, http://http://people.cs.kuleuven.be/~bettina.berendt/teaching/ 25 In which semantic web languages can ontologies be formulated? n RDF Schema is sufficient to specify an ontology with the first 4 components n For the fifth component (logical axioms), need a more expressive language, such as OWL

26. 26 Berendt: Knowledge and the Web, 1st semester 2015/2016, http://http://people.cs.kuleuven.be/~bettina.berendt/teaching/ 26... and what does this mean for inference (given that semantics is so much about entailment)? n RDF Schema is sufficient to specify an ontology with the first 4 components n For the fifth component (logical axioms), need a more expressive language, such as OWL Roughly speaking: RDF Schema allows for inferences up the concept hierarchy OWL permits inferences of first-order logic (more precisely: description logics) OWL permits inferences about the equality of objects/URIs What about the inferences from data mining / correlation / “big data“? What about combinations (e.g. Dedalo)?

27. 27 Berendt: Knowledge and the Web, 1st semester 2015/2016, http://http://people.cs.kuleuven.be/~bettina.berendt/teaching/ 27 Ontologies, decentralization, and bottom-up engineering Communities of users (application builders,...) can n Re-use existing ontologies l Established domain-specific ontologies (e.g., real-estate, medicine, bioinformatics) l „The big one“: Cyc, see www.cyc.comwww.cyc.com l Search for ontologies –See overview at http://en.wikipedia.org/wiki/Ontology_%28information_science%29 #Ontology_libraries http://en.wikipedia.org/wiki/Ontology_%28information_science%29 #Ontology_libraries –Use Sindice with some tricks: http://groups.google.com/group/sindice- dev/browse_thread/thread/831c084c3b5a0214 (or try the Advanced Search directly: http://sindice.com/search ) http://groups.google.com/group/sindice- dev/browse_thread/thread/831c084c3b5a0214http://sindice.com/search n Link to existing ontologies n Extend existing ontologies

28. 28 Berendt: Knowledge and the Web, 1st semester 2015/2016, http://http://people.cs.kuleuven.be/~bettina.berendt/teaching/ 28 Ontologies as conceptual models / schemas; or: Database (knowledge base) = Ontology + Instances My Life and Times Illusions First and Last Freedom Paul McCartney Richard Bach J. Krishnamurti June, 1998 1972 1974 title author date BookCatalogue My Life and Times Paul McCartney June, 1998

29. 29 Berendt: Knowledge and the Web, 1st semester 2015/2016, http://http://people.cs.kuleuven.be/~bettina.berendt/teaching/ 29 Ontologies in RDF: more details n You‘ll be working with it in the exercise session starting today

30. 30 Berendt: Knowledge and the Web, 1st semester 2015/2016, http://http://people.cs.kuleuven.be/~bettina.berendt/teaching/ 30 Outlook The Semantic Web: Motivation and overview Semantics, concepts and ontologies Very brief recap of XML (& why it’s not semantic) RDF and RDFS Linked (Open) Data (LOD)

31. 31 Berendt: Knowledge and the Web, 1st semester 2015/2016, http://http://people.cs.kuleuven.be/~bettina.berendt/teaching/ 31 You have data … How should you structure it? medium-altitude, long-endurance unmanned aerial vehicle 14.7 meters 512 kilograms 70 knots Here's some data about an aircraft: 400 nautical miles

32. 32 Berendt: Knowledge and the Web, 1st semester 2015/2016, http://http://people.cs.kuleuven.be/~bettina.berendt/teaching/ 32 The XML approach is to "wrap" each data item in start/end tags 14.8 meters 512 kilograms 70 knots 400 nautical miles medium-altitude, long-endurance unmanned aerial vehicle RQ-1.xml and define this data schema, e.g. in a DTD

33. 33 Berendt: Knowledge and the Web, 1st semester 2015/2016, http://http://people.cs.kuleuven.be/~bettina.berendt/teaching/ 33 XML Terminology 14.8 meters Start tag End tag Data Element

34. 34 Berendt: Knowledge and the Web, 1st semester 2015/2016, http://http://people.cs.kuleuven.be/~bettina.berendt/teaching/ 34 Why use XML? n It is a universally accepted standard way of structuring data (syntax). n It is a W3C recommendation (W3C = World Wide Web Consortium) n The marketplace supports it with a lot of free/inexpensive tools. n The alternative to using XML is to define your own proprietary data syntax, and then build your own proprietary tools to support the proprietary syntax (Not a very appealing idea). l NB: Saying that the alternative to using XML is to use JSON misses the point (more on this below).

35. 35 Berendt: Knowledge and the Web, 1st semester 2015/2016, http://http://people.cs.kuleuven.be/~bettina.berendt/teaching/ 35 But: What is this XML snippet talking about, i.e., what are the semantics? … What is a Predator?

36. 36 Berendt: Knowledge and the Web, 1st semester 2015/2016, http://http://people.cs.kuleuven.be/~bettina.berendt/teaching/ 36 Predator - which one? n Predator: a medium-altitude, long-endurance unmanned aerial vehicle system. n Predator : one that victimizes, plunders, or destroys, especially for one's own gain. n Predator : an organism that lives by preying on other organisms. n Predator: a company which specializes in camouflage attire. n Predator: a video game. n Predator: software for machine networking. n Predator: a chain of paintball stores.

37. 37 Berendt: Knowledge and the Web, 1st semester 2015/2016, http://http://people.cs.kuleuven.be/~bettina.berendt/teaching/ 37 A little more flexibility through namespaces <myThings xmlns:h=http://www.mySchemas.org/TR/aircraft/ xmlns:f="http://www.yourSchemas.com/animals"> OL231-b 14.8 metres Panthera antelopes

38. 38 Berendt: Knowledge and the Web, 1st semester 2015/2016, http://http://people.cs.kuleuven.be/~bettina.berendt/teaching/ 38... But this doesn‘t solve the fundamental problems 1. What does nesting mean? 2. What do syntactical variations mean? 3. What do linguistic variations mean? 4. How can we extend our knowledge?

39. 39 Berendt: Knowledge and the Web, 1st semester 2015/2016, http://http://people.cs.kuleuven.be/~bettina.berendt/teaching/ 39 1. What does nesting mean? Schema 1 allows for expressions like: Peter Parker...  name being an XML-element of Person means: the person HAS-A... Schema 2 allows for expressions like: Comic-book hero...  type being an XML-element of Person means: the person IS-A... Problems: a) we don‘t know what nesting means, b) even if we do know, we can‘t express this in a machine-readable way (at most build it into an application that uses these XML statements, but that would bury meaning in procedures!)

40. 40 Berendt: Knowledge and the Web, 1st semester 2015/2016, http://http://people.cs.kuleuven.be/~bettina.berendt/teaching/ 40 2. What do syntactical variations mean? Schema 1 allows for expressions like: Peter Parker 1932-04-12... Schema 2 allows for expressions like: Comic-book hero... Problems: a) what does it mean for some information to be an XML- element vs. an XML-attribute? b) even if we do know that they are the same, we can‘t express this in a machine-readable way, for example to combine the information from the two sources (same remark about applications as in 1.)

41. 41 Berendt: Knowledge and the Web, 1st semester 2015/2016, http://http://people.cs.kuleuven.be/~bettina.berendt/teaching/ 41 3. What do linguistic variations mean? Schema 1 allows for expressions like: Peter Parker... Schema 2 allows for expressions like: Peter Parker... Problems: a) we do not know whether elements from different data sources that differ by, e.g. natural, language, are the same or not b) even if we do know that they are the same, we can‘t express this in a machine-readable way, for example to combine the information from the two sources (same remark about applications as in 1.)

42. 42 Berendt: Knowledge and the Web, 1st semester 2015/2016, http://http://people.cs.kuleuven.be/~bettina.berendt/teaching/ 42 4. How can we extend our knowledge? Schema 1 allows for expressions like: Picture http://www.example.org/Pictures/myPic.png Peter Parker... Schema 2 allows for expressions like: http://www.example.org/Pictures/myPic.png CreativeCommons... Problems: a) we cannot refine our schema information by that provided by another source b) even if we can be sure about principal linkability (here: via the URL), we can‘t express this in a machine-readable way, for example to combine the information from the two sources (same remark about applications as in 1.)

43. 43 Berendt: Knowledge and the Web, 1st semester 2015/2016, http://http://people.cs.kuleuven.be/~bettina.berendt/teaching/ 43 Summary: XML not well-suited for conceptual modelling and therefore not suited for truly semantic markup XML makes no commitment on:  Domain-specific ontological vocabulary  Ontological modeling primitives Requires pre-arranged agreement on  &  Only feasible for closed collaboration n agents in a small & stable community n pages on a small & stable intranet Not suited for sharing Web-resources

44. 44 Berendt: Knowledge and the Web, 1st semester 2015/2016, http://http://people.cs.kuleuven.be/~bettina.berendt/teaching/ 44 Wasn‘t there also... “There is another text notation that has all of the advantages of XML, but is much better suited to data-interchange. That notation is JavaScript Object Notation (JSON). The most informed opinions on XML (see for example xmlsuck.org) suggest that XML has big problems as a data- interchange format, but the disadvantages are compensated for by the benefits of interoperability and openness. JSON promises the same benefits of interoperability and openness, but without the disadvantages.” (http://www.json.org/xml.html)http://www.json.org/xml.html

45. 45 Berendt: Knowledge and the Web, 1st semester 2015/2016, http://http://people.cs.kuleuven.be/~bettina.berendt/teaching/ 45 XML and JSON: example (1)

46. 46 Berendt: Knowledge and the Web, 1st semester 2015/2016, http://http://people.cs.kuleuven.be/~bettina.berendt/teaching/ 46 XML and JSON: example (2)

47. 47 Berendt: Knowledge and the Web, 1st semester 2015/2016, http://http://people.cs.kuleuven.be/~bettina.berendt/teaching/ 47 XML and JSON: example (3)

48. 48 Berendt: Knowledge and the Web, 1st semester 2015/2016, http://http://people.cs.kuleuven.be/~bettina.berendt/teaching/ 48 Recap: Wasn‘t there also... “There is another text notation that has all of the advantages of XML, but is much better suited to data-interchange. That notation is JavaScript Object Notation (JSON). The most informed opinions on XML (see for example xmlsuck.org) suggest that XML has big problems as a data- interchange format, but the disadvantages are compensated for by the benefits of interoperability and openness. JSON promises the same benefits of interoperability and openness, but without the disadvantages.” (http://www.json.org/xml.html)http://www.json.org/xml.html... but JSON also shares the limitations of XML when it comes to semantics!

49. 49 Berendt: Knowledge and the Web, 1st semester 2015/2016, http://http://people.cs.kuleuven.be/~bettina.berendt/teaching/ 49 Solution approach of the „higher levels“ of the Semantic Web 1. Break down information into atomic statements: subject-predicate-object 2. Define (in a formal-semantics way) what each component of each statement means a. Give it a URI (uniform resource identifier) to enable uniform meaning specification b. Define languages to say more about (specify) the meaning (by relating it to other units of meaning – cf. a dictionary in which each word is explained by other words) c. (exception: some components may be literals / strings – these are not defined further) 3. The languages mentioned in 2.b. each add more expressivity: 1. RDF: subject-predicate-object statements (in RDF terminology: a resource has a property with a certain value. 2. RDFS: simple ontology building blocks: class, subclass-of relation, use RDF‘s type to denote that (e.g.) an individual is a instance of a class (= make it possible to define a schema and its instances),... 3. OWL: more advanced ontology building blocks: a class (= concept) is disjoint with another one, is the same as another one; a property is functional, symmetric, the inverse of another one;...

50. 50 Berendt: Knowledge and the Web, 1st semester 2015/2016, http://http://people.cs.kuleuven.be/~bettina.berendt/teaching/ 50 Semantic Web vs. Database Advantages of using RDF/RDFS/OWL to define an Ontology: n Extensible: much easier to add new properties. Contrast with a database - adding a new column may break a lot of applications n Portable: much easier to move an OWL document than to move a database. Advantages of using a Database to define an Ontology: n Mature: the database technology has been around a long time and is very mature. n But … by now there is also solid support for RDF(S)/OWL

51. 51 Berendt: Knowledge and the Web, 1st semester 2015/2016, http://http://people.cs.kuleuven.be/~bettina.berendt/teaching/ 51 Outlook The Semantic Web: Motivation and overview Semantics, concepts and ontologies Very brief recap of XML (& why it’s not semantic) RDF and RDFS Linked (Open) Data (LOD)

52. 52 Berendt: Knowledge and the Web, 1st semester 2015/2016, http://http://people.cs.kuleuven.be/~bettina.berendt/teaching/ 52 What is RDF ? What is the role of XML for RDF ? RDF is a data model l the model is domain-neutral, application-neutral l the model can be viewed as directed, labeled graphs or as an object-oriented model (object/attribute/value) RDF data model is an abstract, conceptual layer independent of XML l consequently, XML is a transfer syntax for RDF, not a component of RDF l RDF data often, but not always occur in XML form –Example: Turtle (Terse RDF Triple Language) l Here, we will first concentrate on the conceptual triple form and only then see examples in XML

53. 53 Berendt: Knowledge and the Web, 1st semester 2015/2016, http://http://people.cs.kuleuven.be/~bettina.berendt/teaching/ 53 RDF model RDF “statements” consist of resources (= nodes) which have properties which have values (= nodes,strings) http://www.w3.org/TR/REC-rdf-syntax/ “Ora Lassila” author = subject = predicate = object “http://www.w3.org/TR/REC-rdf-syntax/ has the author Ora Lassila” resource value property

54. 54 Berendt: Knowledge and the Web, 1st semester 2015/2016, http://http://people.cs.kuleuven.be/~bettina.berendt/teaching/ 54 RDF Model Example http://www.w3.org/TR/REC-rdf-syntax/ “Ora Lassila” dc:Creator “1999-02-22” dc:Date “W3C” dc:Publisher

55. 55 Berendt: Knowledge and the Web, 1st semester 2015/2016, http://http://people.cs.kuleuven.be/~bettina.berendt/teaching/ 55 Complex values So far, values of properties have been strings A graph node (corresponding to a resource) also can be the value of a property n arbitrarily complex tree and graph structures are possible n syntactically, values can be embedded (i.e. lexically in-line) or referenced (linked) Example: http://www.w3.org/TR/REC-rdf-syntax/ “Ora Lassila” dc:Creator “ora.lassila@nokia.com” p:EMail p:Name

56. 56 Berendt: Knowledge and the Web, 1st semester 2015/2016, http://http://people.cs.kuleuven.be/~bettina.berendt/teaching/ 56 Complex values (continued) Corresponding triples { “http://www.w3.org/TR/PR-rdf-syntax/”, dc:Creator, x } { x, p:Name, “Ora Lassila” } { x, p:EMail, “ora.lassila@nokia.com” } http://www.w3.org/TR/REC-rdf-syntax/ “Ora Lassila” dc:Creator “ora.lassila@nokia.com” p:EMail p:Name

57. 57 Berendt: Knowledge and the Web, 1st semester 2015/2016, http://http://people.cs.kuleuven.be/~bettina.berendt/teaching/ 57 Containers Containers are collections n they allow grouping of resources (or literal values) It is possible to make statements about the container (as a whole) or about its members individually Different types of containers exist n bag - unordered collection n seq - ordered collection (= “sequence”) n alt - represents alternatives It is also possible to create collections based on URI patterns n for example, all files in a particular web site Duplicate values are permitted n there is no mechanism to enforce unique value constraints

58. 58 Berendt: Knowledge and the Web, 1st semester 2015/2016, http://http://people.cs.kuleuven.be/~bettina.berendt/teaching/ 58 Containers (continued) http://www.w3.org/TR/REC-rdf-syntax “Ora Lassila” rdf:_1 rdf:Seq dc:Creator rdf:Type “Ralph Swick” rdf:_2

59. 59 Berendt: Knowledge and the Web, 1st semester 2015/2016, http://http://people.cs.kuleuven.be/~bettina.berendt/teaching/ 59 Higher-order statements One can make RDF statements about other RDF statements n example: “Ralph believes that the web contains one billion documents” Higher-order statements n allow us to express beliefs (and other modalities) n are important for trust models, digital signatures,etc. n also: metadata about metadata n are represented by modeling RDF in RDF itself

60. 60 Berendt: Knowledge and the Web, 1st semester 2015/2016, http://http://people.cs.kuleuven.be/~bettina.berendt/teaching/ 60 Reification n RDF is not really second-order n But it does provide a built-in predicate vocabulary for reification http://www.w3.org/TR/REC-rdf-syntax“Ora Lassila” dc:Creator “Library of Congress” dc:Creator The dotted box corresponds to the following statements { x, rdf:predicate, “dc:creator” } { x, rdf:subject, “http://www.w3.org/TR/RED-rdf-syntax } { x, rdf:object, “Ora Lassila” } { x, rdf:type, “rdf:statement” }

61. 61 Berendt: Knowledge and the Web, 1st semester 2015/2016, http://http://people.cs.kuleuven.be/~bettina.berendt/teaching/ 61 Reification pers05 ISBN... Author-of NYT claims ISBN... Any statement can be an object graphs can be nested - reification

62. 62 Berendt: Knowledge and the Web, 1st semester 2015/2016, http://http://people.cs.kuleuven.be/~bettina.berendt/teaching/ 62 RDF Schema Defines small vocabulary for RDF: Class, subClassOf, type Property, subPropertyOf domain, range Vocabulary can be used to define other vocabularies for your application domain Person StudentResearcher subClassOf Jeen type hasSuperVisor domain range Frank type hasSuperVisor

63. 63 Berendt: Knowledge and the Web, 1st semester 2015/2016, http://http://people.cs.kuleuven.be/~bettina.berendt/teaching/ 63 RDF Schema syntax in XML

64. 64 Berendt: Knowledge and the Web, 1st semester 2015/2016, http://http://people.cs.kuleuven.be/~bettina.berendt/teaching/ 64 Outlook The Semantic Web: Motivation and overview Semantics, concepts and ontologies Very brief recap of XML (& why it’s not semantic) RDF and RDFS Linked (Open) Data (LOD)

65. 65 Berendt: Knowledge and the Web, 1st semester 2015/2016, http://http://people.cs.kuleuven.be/~bettina.berendt/teaching/ 65 But we can use Web data already! Not all interesting data are hidden from us! There are Web APIs for lots of stuff! There‘s even catalogues of them, e.g. http://www.programmableweb.com/ http://www.programmableweb.com/ But... (just some examples) Stand-aloneEasily interlinkable linkability accessi- bility “open“ “closed“ Google query logs; Typical company data Amazon API; other Web APIs; Many datasets on data.gov, data.gov.be,... Semantic Desktop Linking Open Drug Data project Linked Open Data

66. 66 Berendt: Knowledge and the Web, 1st semester 2015/2016, http://http://people.cs.kuleuven.be/~bettina.berendt/teaching/ 66 What is LOD? (1) n “A way of making the Semantic Web happen“ (it is hoped) n Key concept: leverage the existence of structured data and combine it with the languages and infrastructures of the Web and the Semantic Web

67. 67 Berendt: Knowledge and the Web, 1st semester 2015/2016, http://http://people.cs.kuleuven.be/~bettina.berendt/teaching/ 67 What is LOD? (2) n Tim Berners-Lee: four principles of Linked Data (http://www.w3.org/DesignIssues/LinkedData)http://www.w3.org/DesignIssues/LinkedData l Use URIs to identify things.URIs l Use HTTP URIs so that these things can be referred to and looked up ("dereferenced") by people and user agents.HTTPdereferenceduser agents l Provide useful information about the thing when its URI is dereferenced, using standard formats such as RDF/XML.RDF/XML l Include links to other, related URIs in the exposed data to improve discovery of other related information on the Web. –(e.g. using owl:sameAs ) owl:sameAs

68. 68 Berendt: Knowledge and the Web, 1st semester 2015/2016, http://http://people.cs.kuleuven.be/~bettina.berendt/teaching/ 68 Data items are identified with HTTP URIs pd:cygri Richard Cyganiak dbpedia:Berlin foaf:name foaf:based_near foaf:Person rdf:type pd:cygri = http://richard.cyganiak.de/foaf.rdf#cygri dbpedia:Berlin = http://dbpedia.org/resource/Berlin From http://www.ai.sri.com/~nysmith/slides/aic-seminars/090724-bizer.ppt

69. 69 Berendt: Knowledge and the Web, 1st semester 2015/2016, http://http://people.cs.kuleuven.be/~bettina.berendt/teaching/ 69 Resolving URIs over the Web dp:Cities_in_Germany 3.405.259 dp:population skos:subject Richard Cyganiak dbpedia:Berlin foaf:name foaf:based_near foaf:Person rdf:type pd:cygri From http://www.ai.sri.com/~nysmith/slides/aic-seminars/090724-bizer.ppt

70. 70 Berendt: Knowledge and the Web, 1st semester 2015/2016, http://http://people.cs.kuleuven.be/~bettina.berendt/teaching/ 70 Dereferencing URIs over the Web dp:Cities_in_Germany 3.405.259 dp:population skos:subject Richard Cyganiak dbpedia:Berlin foaf:name foaf:based_near foaf:Person rdf:type dbpedia:Hamburg dbpedia:Muenchen skos:subject pd:cygri From http://www.ai.sri.com/~nysmith/slides/aic-seminars/090724-bizer.ppt

71. 71 Berendt: Knowledge and the Web, 1st semester 2015/2016, http://http://people.cs.kuleuven.be/~bettina.berendt/teaching/ 71 Recall: application in Dedalo (traversing LOD)

72. 72 Berendt: Knowledge and the Web, 1st semester 2015/2016, http://http://people.cs.kuleuven.be/~bettina.berendt/teaching/ 72 The Linked Open Data Cloud (2011)

73. 73 Berendt: Knowledge and the Web, 1st semester 2015/2016, http://http://people.cs.kuleuven.be/~bettina.berendt/teaching/ 73 2014 (to click on details: http://lod-cloud.net/) Linking Open Data cloud diagram 2014, by Max Schmachtenberg, Christian Bizer, Anja Jentzsch and Richard Cyganiak. http://lod- cloud.net/

74. 74 Berendt: Knowledge and the Web, 1st semester 2015/2016, http://http://people.cs.kuleuven.be/~bettina.berendt/teaching/ 74 http://www.lodnav.com/navigate.html

75. 75 Berendt: Knowledge and the Web, 1st semester 2015/2016, http://http://people.cs.kuleuven.be/~bettina.berendt/teaching/ 75 Texts on LOD applications Heath, T. & Bizer, C. (2011). Linked Data: Evolving the Web into a Global Data Space. Chapter 3.Linked Data: Evolving the Web into a Global Data Space. Wood et al. (2014). Linked Data: Structured Data on the Web. http://www.manning.com/dwood/LDSampleCH01.pdf http://www.manning.com/dwood/LDSampleCH01.pdf The Euclid Project Consortium (201x?) Euclid book, section 5.3 Using Linked Data Effectively. http://euclid-project.euhttp://euclid-project.eu Gocebe et al. (2015). Bringing Agility into Linked Data Development: An Industrial Use Case in Logistics Domain. Proc. LDOW. http://events.linkeddata.org/ldow2015/papers/ldow2015_paper_11.pdf

76. 76 Berendt: Knowledge and the Web, 1st semester 2015/2016, http://http://people.cs.kuleuven.be/~bettina.berendt/teaching/ 76 Homework (individual) Read these texts and prepare 3 questions for our invited speakers. Send them to us by email by Monday, 19th October

77. 77 Berendt: Knowledge and the Web, 1st semester 2015/2016, http://http://people.cs.kuleuven.be/~bettina.berendt/teaching/ 77 More on LOD n W3C Linking Open Data community project: http://www.w3.org/wiki/SweoIG/TaskForces/CommunityProje cts/LinkingOpenData http://www.w3.org/wiki/SweoIG/TaskForces/CommunityProje cts/LinkingOpenData n A nice slideset is available at http://www.ai.sri.com/~nysmith/slides/aic-seminars/090724- bizer.ppt http://www.ai.sri.com/~nysmith/slides/aic-seminars/090724- bizer.ppt n A book: Heath, T. & Bizer, Ch. (2011). Linked Data: Evolving the Web into a Global Data Space. Morgan & Claypool. http://linkeddatabook.com http://linkeddatabook.com

78. 78 Berendt: Knowledge and the Web, 1st semester 2015/2016, http://http://people.cs.kuleuven.be/~bettina.berendt/teaching/ 78 Applications with Linked Data (1)

79. 79 Berendt: Knowledge and the Web, 1st semester 2015/2016, http://http://people.cs.kuleuven.be/~bettina.berendt/teaching/ 79 Applications with Linked Data (2)

80. 80 Berendt: Knowledge and the Web, 1st semester 2015/2016, http://http://people.cs.kuleuven.be/~bettina.berendt/teaching/ 80 Applications with Linked Data (3) http://www.w3.org/wiki/SweoIG/TaskForces/CommunityProjects/ LinkingOpenData/Applications

81. 81 Berendt: Knowledge and the Web, 1st semester 2015/2016, http://http://people.cs.kuleuven.be/~bettina.berendt/teaching/ 81 Applications partially with / moving towards Linked Data

82. 82 Berendt: Knowledge and the Web, 1st semester 2015/2016, http://http://people.cs.kuleuven.be/~bettina.berendt/teaching/ 82 PS: What are „semantic technologies“? n encode meanings separately from data and content files, and separately from application code n Often uses elements (e.g. the OWL language) of the Semantic Web n But not necessarily open data n Thus, increasingly popular for example for within-company solutions n See our invited talk on 21 October

83. 83 Berendt: Knowledge and the Web, 1st semester 2015/2016, http://http://people.cs.kuleuven.be/~bettina.berendt/teaching/ 83 Outlook The Semantic Web: Motivation and overview Semantics, concepts and ontologies Very brief recap of XML (& why it’s not semantic) RDF and RDFS Linked (Open) Data (LOD) After the Invited Talks: More on SW: quality; inference

84. 84 Berendt: Knowledge and the Web, 1st semester 2015/2016, http://http://people.cs.kuleuven.be/~bettina.berendt/teaching/ 84 Used sources (unless cited on the slide itself) (From or based on): http://en.wikipedia.org/wiki/Semantic_Web Costello, R.L. & Jacobs, D.B. (2003). A Two Minute Intro to XML. www.daml.org/meetings/2003/05/SWMU/briefings/07_1045_Essential_Building_Bl ocks.ppt www.daml.org/meetings/2003/05/SWMU/briefings/07_1045_Essential_Building_Bl ocks.ppt Unnamed (no date). RDF and XML tutorial. http://lsdis.cs.uga.edu/SemWebCourse/RDF.ppt http://lsdis.cs.uga.edu/SemWebCourse/RDF.ppt Dedalo:: http://2014.eswc-conferences.org/sites/default/files/papers/paper_127.pdf http://ceur-ws.org/Vol-1264/cold2014_TiddiDM.pdf Uschold, „“Where Are the Semantics in the Semantic Web?”, AI Magazine 2003, https://www.aaai.org/ojs/index.php/aimagazine/article/viewFile/1716/1614 https://www.aaai.org/ojs/index.php/aimagazine/article/viewFile/1716/1614 In various places (the texts with many hyperlinks in them): Wikipedia entries on FOAF, the Semantic Web, JSON, concept, semantics, versions 14 Oct. 2015 Picture credits: see PPT „comments“ field

85. 85 Berendt: Knowledge and the Web, 1st semester 2015/2016, http://http://people.cs.kuleuven.be/~bettina.berendt/teaching/ 85 Further references, background reading; acknowledgements Specifications: RDF: http://www.w3.org/RDF/, http://www.w3.org/TR/rdf-primerhttp://www.w3.org/RDF/http://www.w3.org/TR/rdf-primer OWL: http://www.w3.org/TR/owl-featureshttp://www.w3.org/TR/owl-features OWL2: http://www.w3.org/TR/owl2-overview/http://www.w3.org/TR/owl2-overview/ FOAF: http://xmlns.com/foaf/spechttp://xmlns.com/foaf/spec