1. TDT44 Semantic web chapter 2: RDF Resource Description Framework Espen Albert

2. Presentation structure Scenario Problem and solution Concepts RDF/XML Turtle

3. Scenario throughout presentation You are a quality engineer for Nikon, Nikon produces cameras. Assignment Read reviews from the web, and summarize peoples opinions Gather information about products  Deliver feedback to producers How do we write a computer program to gather all these reviews?

4. Problem: The web is not understandable to a machine. Internet today, how do we combine data? Domain specific, can not easily interchange information Different review sites have different formats Represent camera(Nikon D300, D300, Nikon_D300, etc. ) Represent features (Zoom, price range, weight, usability, etc.) Represent rating (5 stars, 1-10, etc.) Represent reviewer (name, facebook, nickname, etc.) Etc. What if it was easy? Scenario: You ask internet what do people say about Nikon cameras you get back “clean” data, only reliable reviews with a rating scale you like and all pros and cons are listed. Job done…

5. Solution –Semantic web RDF Where in relation to the semantic web? Base layer for representing information Story 1999 Resource Description Framework specification by W3C 2004 the updated RDF specifications consequence of semantic web describe web resources  describe any resource 6 documents. See book and W3C if you are interested in the specifics Definition RDF – Resource Description Framework a standard published by W3C that can be used to represent distributed information/knowledge in a way that computer applications can use and process it in a scalable manner. A language enabling computers and humans to describe entities, both abstract and real, over the web in a format with meaningful non ambiguous data A framework to standardize communication for humans and machines so everyone can understand Components of solution Need: Express any information anyone can think of Why we use triples Need: Mechanism to connect distributed information over the Web / Have a way of talking about the same/unique concepts Why we use vocabularies, and URIs WHO? DO?

6. Concepts RDF Statement/triple Subject|Predicate|Object Resource|Property|Value URI –Uniform Resource Identifier General identifier for Abstract concepts, Human being, Product, Physical location and URL Examples URL relation to URI? URLs can be directly retrieved from the web, URL subset of URI. Change Only identifier  Required to return content, because of linked data project 2 types Slash = normal Hash (aka. URI Reference, URIref) = normal URI + # + fragment identifier Hash preferred because they are dereferenceable URI, no need for content negotiation mechanism, slash could have different file types Vocabulary Set of URIs with a common prefix RDF Model RDF Graph - Collection of statements Statements – Set of triples

7. Statements Examples Nikon_D300 weighs 0.6kg What are the subject, predicate and object? S: Nikon_D300 P: Weighs O: 0.6kg Nikon_D300 is manufactured by Nikon What are the subject, predicate and object? S: Nikon_D300 P: manufactured by O: Nikon Which of the three (S, P, O) must be a URI? Predicate. A subject can be a “blank node”. An object can be a “literal” or “blank node” How do we serialize this? RDF/XML, Turtle, N3-Notation, N- triples

8. RDF/XML 1 Nikon_D300 weighs 0.6kg RDF/XML use the RDF vocabulary found @ http://www.w3.org/1999/02/22-rdf-syntax-ns# with rdf as prefix http://www.w3.org/1999/02/22-rdf-syntax-ns# xmlns:”prefix” = vocabulary Statement: literal

9. RDF/XML 2 Nikon_D300 manufactured_by Nikon Fill in the missing part: Nikon_D300 and Manufactured_by is found in the myCamera vocabulary Nikon is identified by: "http://www.dbpedia.org/resource/Nikon" Note difference from previous : Statement: literal

10. RDF/XML 3 Nikon_D300 is_a DSLR (Digital single-lens reflex) Fill in the missing part: All resources is found in the myCamera vocabulary

11. RDF/XML 4 Nikon_D300 is_a DSLR (Digital single-lens reflex) Switch to using rdf:type instead Alternative

12. RDF/XML 5 Combining statements for one subject Nikon_D300 is a DSLR Nikon_D300 manufactured_by Nikon

13. RDF/XML 6 Nesting statements

14. RDF/XML 7 literals Nikon_D300 weighs 0.6kg “0.6kg” is called a literal. Other examples “5 stars”, “Espen”, “0,33” None of these statements mean the same: These are equal

15. RDF/XML 8 rdf:value Nikon_D300 weights 0.6kg Note line 16: No rdf:about. This is called a blank node. The camera has a weight that has two properties value and unit. Could have used rdf:nodeID Blank nodes are used to Model n-ary relationships Some class that will never be used outside graph

16. RDF/XML 9 rdf:datatype for literals Nikon_D300 weights 0.6kg, Nikon_D300 model “D300” Note line 14a and 17a: Both datatypes are written with full URI. And the two properties it is used for. Custom = myCamera:model & rdf:value rdf:parseType used instead of rdf:Description Avoidance of full URI http://www.w3.org/2001/XMLSchema

17. Turtle Most popular of the alternatives to RDF/XML Syntax also similar to SPARQL ttl = http://www.w3.org/2008/turtle#turtlehttp://www.w3.org/2008/turtle#turtle Format Example

18. Turtle 2 Literals language: Datatype:

19. Turtle 3 @base can also be used to change the in scope URI What is the URI? subj1? http://liyangyu.com/ns0/subj1 subj2? http://liyangyu.com/ns0/foo/subj2 subj3? http://liyangyu.com/ns0/foo/bar#subj3 obj4? http://liyangyu.com/ns1/obj4 a to replace rdf:type

20. Turtle 4 Multiple statements for subject with same predicate use “,” Multiple statements for subject with different predicate use “;”

21. Turtle 5

22. Summary Need: Express any information anyone can think of Why we use triples Need: Mechanism to connect distributed information over the Web / Have a way of talking about the same/unique concepts Why we use vocabularies, and URIs RDF What is your definition of RDF?

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28. RDF/XML 10 Avoid writing rdf:about=“full URI” In-scope base URI. Since the example is located @ http://ww.liyangyu.com/rdf/review.rdf The full URI: http://ww.liyangyu.com/rdf/review.rdf#Nikon_D300 http://ww.liyangyu.com/rdf/review.rdf http://ww.liyangyu.com/rdf/review.rdf#Nikon_D300 To change in-scope base URI:

29. RDF/XML 11 Collection of literals or resources rdf:bag  Unordered rdf:seq  Ordered rdf:alt  Non-duplicates, e.g. list of alternative stores selling x

30. RDF/XML 12 Reification – description of statements Example: The creator of the statement is liyang http://www.purl.org/metadata/dublin-core# - Dublin Core vocabulary used for properties of a given document http://www.purl.org/metadata/dublin-core# Problems No built in mechanism to understand that the URI myCamera:statement_01 is created for a statement Up to RDF application to decide which statement the reification belongs to Specifying subject, predicate, object could match multiple statements if we are in a global context