• Resource Description Framework (RDF) is a data model that is used to describe resources
• Physical things
• Abstract concepts
• Numbers and strings
• We use the term resource and entity synonymously here
• It is a universal, machine readable data exchange format
• Resources are described using triples (subject, predicate, object)
• A triple captures the relationship (predicate) between a subject and an object

• <Delhi> <capitalOf> <India>
• RDF triple is called a RDF Statement
• Triple can be represented as a directed labelled graph

• URL (Uniform Resource Locator)
• It is a mechanism to specify and locate a web resource on a computer network.
• Eg: http://, ftp://
• URN (Uniform Resource Name)
• They are persistent location independent identifiers that use the urn scheme.
• Eg: ISBN of a book is a URN used to identify a book uniquely

• URI (Uniform Resource Identifier)
• It is an identifier that can uniquely and unambiguously identify resources
• ASCII encoding is used in the identifiers
• URL and URN are type of URIs. URIs and URNs need not be resolvable to a location, which is the case with URL
• Eg: http://www.w3.org/2002/07/owl#
• IRI (International Resource Identifier)
• IRI is similar to URI except that the character set for encoding the identifier is Universal Character Set (UTF-8)
• Eg: é, ö could be used in IRI

• Subject, Predicate, and Object in a triple are identified by IRIs
• http://www.example.org/~joe/contact.rdf#joesmith
• http://xmlns.com/foaf/0.1/homepage
• http://www.example/org/~joe
• Literals and blank nodes do not have IRIs

• A blank node does not have a name associated with it
• It is similar to anonymous classes in Java, C++
• It indicates the existence of something but we will not be using or saying anything about the name of that thing

• It does not have an IRI
• Blank node identifiers have only local scope
• No global identity unlike other nodes with IRIs
• It is not a literal
• It can be used as a subject or object

• RDF statements can be grouped into multiple graphs
• Each graph can have a name associated with it (named graphs), which is an IRI
• An RDF dataset is a collection of graphs
• Exactly one default (unnamed) graph that may be empty
• Zero or more named graphs
• Graph names are unique within a RDF dataset
• Blank nodes can be shared by graphs in a RDF dataset

1. Graph name (IRI): http://example.org/bob
• <Bob> <is a> <person>.
• <Bob> <is a friend of> <Alice>.
• <Bob> <is born on> <the 4th of July 1990>.
• <Bob> <is interested in> <the Mona Lisa>.
2. Graph name (IRI): https://www.wikidata.org/wiki/Special:EntityData/Q12418
• <Leonardo da Vinci> <is the creator of> <the Mona Lisa>.
• <The video 'La Joconde à Washington'> <is about> <the Mona Lisa>

• There are different serialization formats for writing RDF graphs
• They are all logically equivalent and lead to same triples
• Turtle family of RDF serialization formats
• N-Triples
• Turtle
• TriG
• N-Quads
• JSON-LD
• RDFa
• RDF/XML

N-Triples

• It is a line based, plain text format to encode a RDF graph
• It is a sequence of subject, predicate, and object separated by whitespace and terminated by dot
• IRIs are written as absolute IRIs (not shortcuts) and are enclosed in angular brackets
• Literals are written in double quotes followed by datatype or language tag
• Datatype IRI is preceded by "^^"
• Language tag is preceded by "@"
• Blank nodes are expressed as _: followed by blank node label
• _:alice <http://xmlns.com/foaf/0.1/knows> _:bob .

N-Triples

1. <http://example.org/bob#me> <http://www.w3.org/1999/02/22-rdf-syntax-ns#type> <http://xmlns.com/foaf/0.1/Person> .
2. <http://example.org/bob#me> <http://xmlns.com/foaf/0.1/knows> <http://example.org/alice#me> .
3. <http://example.org/bob#me> <http://schema.org/birthDate> "1990-07-04"^^<http://www.w3.org/2001/XMLSchema#date> .
4. <http://example.org/bob#me> <http://xmlns.com/foaf/0.1/topic_interest> <http://www.wikidata.org/entity/Q12418> .
5. <http://www.wikidata.org/entity/Q12418> <http://purl.org/dc/terms/title> "Mona Lisa" .
6. <http://www.wikidata.org/entity/Q12418> <http://purl.org/dc/terms/creator> <http://dbpedia.org/resource/Leonardo_da_Vinci> .
7. <http://data.europeana.eu/item/04802/243FA8618938F4117025F17A8B813C5F9AA4D619> <http://purl.org/dc/terms/subject> <http://www.wikidata.org/entity/Q12418> .

Turtle

• Turtle is the Terse RDF Triple Language
• It is an extension of N-Triples with syntactic shortcuts
• Namespace prefix
• Predicate lists
• Object lists

Turtle

BASE   <http://example.org/>
PREFIX foaf: <http://xmlns.com/foaf/0.1/>
PREFIX xsd: <http://www.w3.org/2001/XMLSchema#>
PREFIX schema: <http://schema.org/>
PREFIX dcterms: <http://purl.org/dc/terms/>
PREFIX wd: <http://www.wikidata.org/entity/>
						

Turtle

• Predicate lists are triples with the same subject but different predicates and objects
• Semi colon is used as a separator

<bob#me>
	a foaf:Person ;
	foaf:knows <alice#me> ;
	schema:birthDate "1990-07-04"^^xsd:date ;
	foaf:topic_interest wd:Q12418 .
						

Turtle

• Object lists are triples with the same subject and predicate, but different object
• Comma is used as a separator

<ex:spiderman> foaf:name "Spiderman", "Человек-паук"@ru  .
						

Turtle

• Two types of IRIs - relative and absolute
• Absolute IRI
• <http://one.example/subject1>
• Relative IRI

BASE <http://one.example/>
<subject1> <predicate1> <object1> .
						

PREFIX p: <http://one.example/>
p:subject1 p:predicate1 p:object1> .
						

TriG

• Extension of Turtle that supports multiple graphs

GRAPH <http://example.org/bob>
{
    <bob#me>
	a foaf:Person ;
        foaf:knows <alice#me> ;
        schema:birthDate "1990-07-04"^^xsd:date ;
        foaf:topic_interest wd:Q12418 .
}
						

TriG

• Default graphs

<http://example.org/bob>
        dcterms:publisher <http://example.org/crc> ;
        dcterms:rights <http://creativecommons.org/licenses/by/3.0/> .
						

TriG

N-Quads

• Extends N-Triples with a fourth element to the line which is the graph IRI of the triple

<http://example.org/bob#me> <http://www.w3.org/1999/02/22-rdf-syntax-ns#type> <http://xmlns.com/foaf/0.1/Person> <http://example.org/bob> .
<http://example.org/bob#me> <http://xmlns.com/foaf/0.1/knows> <http://example.org/alice#me> <http://example.org/bob> .
						

<http://example.org/bob> <http://purl.org/dc/terms/publisher> <http://example.org> .
<http://example.org/bob> <http://purl.org/dc/terms/rights> <http://creativecommons.org/licenses/by/3.0/> .
						

JSON-LD

• Provides JSON sytanx for RDF graphs
• JSON-LD can be used to transform JSON to RDF
• JSON objects are given universal identifiers in JSON-LD
• This helps in referring to objects in other JSON documents anywhere on the Web

JSON-LD

{
"@context": "example-context.json",
"@id": "http://example.org/bob#me",
"@type": "Person",
"birthdate": "1990-07-04",
"knows": "http://example.org/alice#me",
"interest": {
	"@id": "http://www.wikidata.org/entity/Q12418",
	"title": "Mona Lisa",
	"subject_of": "http://data.europeana.eu/item/04802/243FA8618938F4117025F17A8B813C5F9AA4D619",
	"creator": "http://dbpedia.org/resource/Leonardo_da_Vinci"
    }
}
						

RDFa

• It is used to embed RDF within HTML and XML documents
• Search engines can make use of the structured data (schema.org, Rich Snippets) to enrich search results

RDFa

<body prefix="foaf: http://xmlns.com/foaf/0.1/
	schema: http://schema.org/
	dcterms: http://purl.org/dc/terms/">
<div resource="http://example.org/bob#me" typeof="foaf:Person">
	<p>
		Bob knows <a property="foaf:knows" href="http://example.org/alice#me">Alice</a>
        and was born on the <time property="schema:birthDate" datatype="xsd:date">1990-07-04</time>.
    </p>
	<p>
		Bob is interested in <span property="foaf:topic_interest"
        resource="http://www.wikidata.org/entity/Q12418">the Mona Lisa</span>.
      </p>
  <</div>
</body>
						

RDF/XML

• Provides XML syntax for RDF graphs
• There is good tool support for XML
• This used to be the only syntax that was available to serialize RDF

RDF/XML

<?xml version="1.0" encoding="utf-8"?>
<rdf:RDF
	xmlns:dcterms="http://purl.org/dc/terms/"
	xmlns:foaf="http://xmlns.com/foaf/0.1/"
	xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
	xmlns:schema="http://schema.org/">
	<rdf:Description rdf:about="http://example.org/bob#me">
		<rdf:type rdf:resource="http://xmlns.com/foaf/0.1/Person"/>
		<schema:birthDate rdf:datatype="http://www.w3.org/2001/XMLSchema#date">1990-07-04</schema:birthDate>
		<foaf:knows rdf:resource="http://example.org/alice#me"/>
		<foaf:topic_interest rdf:resource="http://www.wikidata.org/entity/Q12418"/>
	</rdf:Description>
</rdf:RDF>
						

• RDFS is a semantic extension of RDF
• It provides the vocabulary for the RDF data
• It provides a mechanism to describe groups of related resources (classes) and the relationships between these resources (properties)
• Classes
• Related resources can be categorized as a class
• A class is defined using rdfs:Class
• Members of the class are known as instances
• Classes can be subclass of another class. This is defined using rdfs:subClassOf
• A Resource is the class of everything, i.e., class of all classes

• Properties
• It is a relation between subject resources and object resources
• A property/predicate is defined using rdf:Property
• Subproperties can be stated using rdfs:subPropertyOf
• hasSon rdfs:subPropertyOf hasChild
• A property can have domain and range, which can be defined using rdfs:domain and rdfs:range respectively
• • If multiple domains/ranges are defined then the domain/range of the property is the intersection of all the defined domains/ranges

• Other frequently used RDFS schema elements
• rdf:type
• rdfs:Literal
• rdfs:label
• rdfs:comment

Examples

1. Person rdf:type rdfs:Class .
2. Father rdfs:subClassOf Person .
3. hasAge rdf:type rdf:Property .
4. hasSon rdfs:subPropertyOf hasChild .
5. hasAge rdfs:domain Person
6. hasAge rdfs:range rdfs:Literal .
7. wd:Q12418 rdfs:Label "Mona Lisa" .
8. wd:Q12418 rdfs:comment "Wikidata ID for Mona Lisa" .

Conventions

• We use the following conventions in the entailment rules
• S represents an RDF graph
• aaa, bbb represents predicate of a triple
• xxx, yyy, zzz represents either the subject or object of a triple
• sss represents a literal
• ddd represents a datatype

RDF Entailment Patterns

• If ex:a    ex:p    "123"^^xsd:integer .   then
• ex:a    ex:p    _:x .   and
• _:x    rdf:type    xsd:integer .

RDF Entailment Patterns

• If ex:a    ex:p    "123"^^xsd:integer .   then
• ex:p    rdf:type    rdf:Property .

RDFS Entailment Patterns

• If ex:a    ex:p    "123"^^xsd:integer .   then
• xsd:integer    rdf:type    rdfs:Datatype .

RDFS Entailment Patterns

• If ex:worksAt    rdfs:domain    ex:Employee .   and
      ex:john    ex:worksAt    ex:ibm .   then
• ex:john    rdf:type    ex:Employee .

RDFS Entailment Patterns

• If ex:worksAt    rdfs:range    ex:Organization .   and
      ex:john    ex:worksAt    ex:ibm .   then
• ex:ibm    rdf:type    ex:Organization .

RDFS Entailment Patterns

RDFS Entailment Patterns

RDFS Entailment Patterns

RDFS Entailment Patterns

• If ex:hasSon    rdfs:subPropertyOf    ex:hasChild .   and
      ex:john    ex:hasSon    ex:mike .   then
• ex:john    ex:hasChild    ex:mike .

RDFS Entailment Patterns

RDFS Entailment Patterns

• If ex:Employee    rdfs:subClassOf    ex:Person .   and
      ex:john    rdf:type    ex:Employee .   then
• ex:john    rdf:type    ex:Person .

RDFS Entailment Patterns

RDFS Entailment Patterns

RDFS Entailment Patterns

• If ex:CarBrandsBag    rdf:_1    ex:honda .   and
      ex:CarBrandsBag    rdf:_2    ex:toyota .  
      rdf:_1    rdf:type    rdfs:ContainerMembershipProperty .   then
• rdf:_1    rdfs:subPropertyOf    rdfs:member .

RDFS Entailment Patterns

• Online RDF Editor: http://linkeddata.uriburner.com/rdf-editor/
• Online RDF Visualization: http://visgraph3.org/
• Domain: Delhi Public Transportation
• Road Transport (Bus, AutoRickshaw, Taxi, CycleRickshaw)
• Rail Transport (Metro)
• Air Transport
• Properties: hasCapacity, hasLocation, hasSource, hasDestination

• Pick a domain of your choice and build an RDF graph

RDF Editors

1. http://linkeddata.uriburner.com/rdf-editor/
2. https://bitbucket.org/dotnetrdf/dotnetrdf/wiki/UserGuide/Tools/rdfEditor
3. http://www.linkeddatatools.com/rdf-studio
4. https://marketplace.eclipse.org/content/komma-rdf-eclipse
5. https://github.com/AKSW/Xturtle
6. https://atom.io/packages/language-rdf
7. https://github.com/e-e-e/sublime-turtle-syntax, https://github.com/abcoates/sublime-text-turtle-sparql
8. https://sourceforge.net/projects/veudas/

RDF Visualization Tools

1. http://www.easyrdf.org/converter
2. http://rhizomik.net/html/redefer/rdf2svg-form/
3. https://github.com/usc-isi-i2/ontology-visualization
4. https://franz.com/agraph/gruff/
5. https://github.com/idafensp/ar2dtool
6. https://github.com/dyreriket/rdfvizler
7. http://activearchives.org/wiki/Visualizing_RDF
8. http://visgraph3.org/

RDF Validators

1. https://www.w3.org/RDF/Validator/
2. http://rdfvalidator.mybluemix.net/
3. http://ttl.summerofcode.be/