RDFS. Suresh Manandhar* & Dimitar Kazakov

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1 ARIN KR Lecture 3 RDFS Suresh Manandhar* & Dimitar Kazakov *Several of these slides are based on tutorial by Ivan Herman (W3C) reproduced here with kind permission. All changes and errors are mine. 1 Lecture Overview! Limitations of RDF! RDFS (RDF Schema) 2 1

2 Camera shop example! Task to build a knowledge base for an online camera shop using RDF ### This info can be public visible to all rdf: : dbpedia: foaf: < :Nikon_D300 rdf:type :DSLR. :Nikon_D300 :manufactured_by dbpedia:nikon. :Nikon_D300 :model "D300". :Nikon_D300 :weight "0.6_kg". :Nikon_D300 :reviewed_by :Reviewer_1. :Reviewer_1 foaf:givenname "John". :Reviewer_1 foaf:family_name "Smith. Camera example adapted from Liyang Yu book. 3 Camera shop example ### This info is stored in private internal db :Nikon_D300 :bought_by :Cust_5636. :Cust_5636 foaf:givenname Sally". :Cust_5636 foaf:family_name Douglas. :Cust_5636 :address_line1 Heslington Lane. 4 2

3 Problems with the Camera shop KB! Nikon_D500 is a camera type and not an instance! Does not permit keeping an inventory (with different serial numbers for each camera)! Does not allow subclasses for types! RDF really is an instance-level (i.e. graph level) KR language! Can only represent graphs! Cannot describe types of graphs 5 Need for RDF schemas (RDFS)! First step towards the extra knowledge :! define the terms we can use! what restrictions apply! what extra relationships are there?! Officially: RDF Vocabulary Description Language! the term Schema is retained for historical reasons 6 3

4 Classes, resources,! Think of well known traditional vocabularies:! use the term novel! every novel is a fiction! «The Glass Palace» is a novel! etc.! RDFS defines resources and classes:! everything in RDF is a resource! classes are also resources, but! they are also a collection of possible resources (i.e., individuals )! fiction, novel, 7 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 subclassof Person subclassof Student domain hassupervisor range Researcher type Frank hassupervisor type Jeen 8 4

Classes in RDF(S) rdfs:class rdf:type http:// isbn/000651409x rdf:type #Novel @prefix rdf: @prefix rdfs: <http://www.w3.org/1999/02/22-rdf-syntax-ns#>. <http://www.w3.org/2000/01/rdf-schema#>.

5 Classes in RDF(S) rdfs:class rdf:type isbn/ x rdf:type rdfs: < < :Novel rdf:type rdfs:class. < /isbn/ x> rdf:type :Novel. Note: a is shorthand for rdf:type. Equivalently: :Novel a rdfs:class. 9 Inferred properties #Fiction isbn/ x rdf:type rdf:type #Novel rdf:subclassof Can infer: (< /isbn/ x> rdf:type #Fiction)! is not in the original RDF data! but can be inferred from the RDFS rules! RDFS environments return that triple, too 10 5

Inference: let us be formal! The RDFS document has a list of (33) entailment rules:! if such and such triples are in the graph, add this and this! do that recursively until the graph does not change!

6 Inference: let us be formal! The RDFS document has a list of (33) entailment rules:! if such and such triples are in the graph, add this and this! do that recursively until the graph does not change! The relevant rule for our example: If: U rdfs:subclassof X. V rdf:type U. Then add: V rdf:type X. 11 Properties! Property is a special class (rdf:property)! properties are also resources identified by URI-s! There is also a possibility for a sub-property! all resources bound by the sub are also bound by the other! Range and domain of properties can be specified! i.e., what type of resources serve as object and subject 12 6

7 Properties (cont.)! Properties are also resources (named via URI s)! So properties of properties can be expressed as RDF properties! this twists your mind a bit, but you can get used to it! For example, (P rdfs:domain C) means:! P is a property! C is a class! when using P, I can infer that the subject is of type C 13 Property specification example 14 7

Property specification } In Turtle: @prefix my: <http://mysite.com/>. @prefix rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#>.

my:title rdfs:domain my:fiction; rdfs:range rdfs:literal. 15 What does this mean?! new relations can be deduced.

8 Property specification } In my: rdf: rdfs: < my:title a rdf:property. my:fiction a rdfs:class. my:title rdfs:domain my:fiction; rdfs:range rdfs:literal. 15 What does this mean?! new relations can be deduced. Indeed, if :title rdf:type rdf:property; rdfs:domain :Fiction; rdfs:range rdfs:literal. < /isbn/ x> :title "The Glass Palace". a reasoning engine can infer that: < /isbn/ x> rdf:type :Fiction. 16 8

Literals! Literals may have a data type! floats, string, integers, booleans, etc., defined in XML Schemas! full XML fragments 17 Examples for datatypes In Turtle @prefix xsd: <http://www.w3.

9 Literals! Literals may have a data type! floats, string, integers, booleans, etc., defined in XML Schemas! full XML fragments 17 Examples for datatypes In xsd: < < /isbn/ x> :page_number "543"^^xsd:integer ; :publ_date "2000"^^xsd:gYear ; :price "6.99"^^xsd:float. Same in RDF/XML <rdf:description rdf:about=" /isbn/ x"> <page_number rdf:datatype=" <publ_date rdf:datatype=" <price rdf:datatype=" </rdf:description> 18 9

Examples for language tags In Turtle <http:// /isbn/000651409x> :title "The Glass Palace"@en ; fr:titre "Le palais des mirroirs"@fr.

10 Examples for language tags In Turtle < /isbn/ x> :title "The Glass ; fr:titre "Le palais des Same in RDF/XML <rdf:description rdf:about=" /isbn/ x"> <title xml:lang="en">the Glass Palace</title> <fr:titre xml:lang="fr">le palais des mirroirs</fr:titre> </rdf:description> 19 Camera shop example! Task to build a knowledge base for an online camera shop using RDF ### This info can visible to all rdf: : dbpedia: foaf: < :Nikon_D300 rdf:type :DSLR. :Nikon_D300 :manufactured_by dbpedia:nikon. :Nikon_D300 :model "D300". :Nikon_D300 :weight "0.6_kg". :Nikon_D300 :reviewed_by :Reviewer_1. :Reviewer_1 foaf:givenname "John". :Reviewer_1 foaf:family_name "Smith

11 Camera shop example ### This info is stored in private internal db :Nikon_D300 :bought_by :Cust_5636. :Cust_5636 foaf:givenname Sally". :Cust_5636 foaf:family_name Douglas. :Cust_5636 :address_line1 Heslington Lane. 21 Extending Camera shop example! Lets describe some hierarchy 22 11

Class/SubClass specification in RDFS @prefix rdfs: <http://www.w3.org/2000/01/rdf-schema#>. @prefix : <http://www.shop.com/camera#>. @prefix foaf: <http://xmlns.com/foaf/0.1/>. :Camera a rdfs:class.

:Nikon_D300 rdfs:subclassof :DSLR. :PointAndShoot rdfs:subclassof :Digital. :Photographer rdfs:subclassof foaf:person. :Journalist rdfs:subclassof foaf:person.

12 Class/SubClass specification in rdfs: : foaf: < :Camera a rdfs:class. :Body a rdfs:class. :Lens a rdfs:class. :ValueRange a rdfs:class. :Digital rdfs:subclassof :Camera. :FilmCamera rdfs:subclassof :Camera. :DSLR rdfs:subclassof :Digital. :Nikon_D300 rdfs:subclassof :DSLR. :PointAndShoot rdfs:subclassof :Digital. :Photographer rdfs:subclassof foaf:person. :Journalist rdfs:subclassof foaf:person. :PhotoJournalist rdfs:subclassof :Photographer. :PhotoJournalist rdfs:subclassof :Journalist. 23 Extending Camera shop example! Lets describe some properties/relations Domain Range reviewer Camera PhotoJournalist Camera Camera Camera ValueRange ValueRange lens Maker shutterspeed minvalue maxvalue Lens Maker ValueRange float float 24 12

Specifying relations in RDFS @prefix dbpedia: <http://www.dbpedia.org/resource/>. @prefix Maker: <http://dbpedia.org/resource/public_company>.

Maker: a rdf:property; rdfs:domain :Camera; rdfs:range Maker:. 25 Lower level ontology!

13 Specifying relations in dbpedia: Maker: < :reviewer a rdf:property; rdfs:domain :Camera; rdfs:range :PhotoJournalist. :lens a rdf:property; rdfs:domain :Camera; rdfs:range :Lens. Maker: a rdf:property; rdfs:domain :Camera; rdfs:range Maker:. 25 Lower level ontology! Need to add knowledge specific to dbpedia: Maker: < :Nikon_D300 Maker: dbpedia:nikon. :Nikon_D300 :lens :Nikon_F30Lens. :Nikon_D300 :lens :Nikon_F50Lens

Lower level ontology! Needs to obey the constraints of the upper ontology! i.e. needs

Maker Nikon 27 Finally add the instances!

############################################################## ### Database of Cameras

14 Lower level ontology! Needs to obey the constraints of the upper ontology! i.e. needs to obey Domain/Range constraints Camera Maker Maker subclassof subclassof Nikon_D300 Maker Nikon 27 Finally add the instances! Now we can populate our database of instances ############################################################## ### Database of Cameras i.e. Camera inventory ############################################################## :Nikon_D300_sn rdf:type :Nikon_D300. :Nikon_D300_sn rdf:type :Nikon_D

Finally add the instances! Next, the transaction and reviewer database ################################################################## ### Buying Database i.e. Transaction database ################################################################## :Nikon_D300_sn8321686 :bought_by :Cust1242.

15 Finally add the instances! Next, the transaction and reviewer database ################################################################## ### Buying Database i.e. Transaction database ################################################################## :Nikon_D300_sn :bought_by :Cust1242. ################################################################# ### Reviewing Database ################################################################# :Nikon_D300 :reviewer :John_Smith. 29 Some predefined structures (collections, containers) 30 15

Predefined classes and properties! RDF(S) has some predefined classes and properties! These are not new concepts in the RDF Model, just resources with an agreed semantics! Examples:! collections (a.k.

16 Predefined classes and properties! RDF(S) has some predefined classes and properties! These are not new concepts in the RDF Model, just resources with an agreed semantics! Examples:! collections (a.k.a. lists)! containers: sequence, bag, alternatives! rdfs:comment, rdfs:seealso, rdf:value 31 Collections (lists)! We could have the following statement:! The book inventory is a «blank node» that consists of < /isbn/ x>, < /isbn/000xxxx>,! But we also want to express the constituents in this order! Using blank nodes is not enough 32 16

../isbn/000651409x"/> <rdf:description rdf:about="http://.

17 Collections (lists) (cont.)! Familiar structure for programmers 33 The same in RDF/XML and Turtle <rdf:description rdf:about="#inventory"> <a:consistsof rdf:parsetype="collection"> <rdf:description rdf:about=" <rdf:description rdf:about=" <rdf:description rdf:about=" </a:consistsof> </rdf:description> :Inventory a:consistsof (< < :Inventory a:consistsof [ rdf:first < rdf:rest [rdf:first < rdf:rest [rdf:first < rdf:rest nil ] ] ]

Sequences! Use the predefined:! RDF Schema class Seq! RDF properties rdf:_1, rdf:_2,!

In RDF/XML: <rdf:description rdf:about="#inventory"> <a:consistsof> <rdf:description>

18 Sequences! Use the predefined:! RDF Schema class Seq! RDF properties rdf:_1, rdf:_2,! The agreed semantics is of a sequential containment 35 Sequences serialized! In RDF/XML: <rdf:description rdf:about="#inventory"> <a:consistsof> <rdf:description> <rdf:type rdf:resource=" <rdf:_1 rdf:resource=" </rdf:description> </a:consistsof> </rdf:description/> In Turtle: :Inventory a:consistsof [ rdf:type < rdf:_1 < ]

19 Other containers! Also defined in RDFS! rdf:bag! a general bag, no particular semantics attached! rdf:alt! agreed semantics: only one of the constituents is valid! Note: these containers are incompletely defined semantically; it is better not to use them! use repeated predicates for bags! use lists for sequences 37 Reference: 38 19

20 Reference: 39 Reference: 40 20

21 How to create RDF Data? (Microformats, GRDDL, RDFa, POWDER) 41 Simple approach! Write RDF/XML, RDFa, or Turtle manually! In some cases that is necessary, but it really does not scale! Alternatively, design the RDFS schema and let applications generate the data! Alternatively, 42 21

22 Microformats! Not a Semantic Web specification, originally! there is a separate microformat community! Approach: re-use (X)HTML attributes and elements to add meta @title,! different agreements for different applications! It is not a specification per se, rather a common methodology! each vocabulary has its own, independent specification 43 Microformat example: hcalendar! Goal: markup calendaring information on your HTML page! use a community agreement using, eg, for event name! abbr element for for date values! etc.! Automatic procedures (ie, calendaring applications) may then get to the right data 44 22

23 A more general solution: microdata! Part of HTML5 standard! It is like microformats in that:! primary goal is to use simple vocabularies! it is bound to HTML! relatively easy to understand and use! it has not been defined with RDF in mind ( RDF is a bonus)! It is not like microformats in that:! it uses dedicated attributes! it is generic, i.e., it can be used with any vocabulary! the specification does include a generic mapping to RDF 45 Microdata example <section itemscope itemtype=" Hello, my name is <span itemprop="name">john Doe</span>, I am a <span itemprop="jobtitle">graduate research assistant</span> at the <span itemprop="affiliation">university of Dreams</span>. My friends call me <span itemprop="additionalname">johnny</span>. You can visit my homepage at <a href=" itemprop="url"> <section itemprop="address" itemscope itemtype=" PostalAddress"> I live at <span itemprop="streetaddress">1234 Peach Drive</span>, <span itemprop="addresslocality">warner Robins</span>, <span itemprop="addressregion">georgia</span>. </section> </section> Example from wikipedia; check out

Semantic Web In Depth: Resource Description Framework. Dr Nicholas Gibbins 32/4037

Semantic Web In Depth: Resource Description Framework Dr Nicholas Gibbins 32/4037 nmg@ecs.soton.ac.uk RDF syntax(es) RDF/XML is the standard syntax Supported by almost all tools RDF/N3 (Notation3) is also