• Notes and exercises: http://wbtc.bfh.ch/2015/linked-data
• Important stuff: Design Issues: Architectural and philosophical points
• Email: sarven.capadisli@bfh.ch

• Web / Linked Data
• HTTP, URI (the fundamentals)
• RDF data model (language) and syntaxes
• SPARQL (querying for RDF)

Illustration by Sandro Hawke

• An application protocol that is at the core of data communication on WWW
• Version 1.1 used mostly, 2.0 on the way
• It has Request methods (e.g., GET, POST, PUT, DELETE)
• Responses with status codes (e.g., 200 OK, 301 Moved Permanently, 303 See Other, 404 Not Found) [seeAlso cats]

• HTTP GETing a particular representation of a resource:
• Includes HTTP Accept headers when requesting, HTTP Content-type in response

http://dbpedia.org/resource/Switzerland has no information on its nature. Can it return HTML, RDF?

1. Request: I accept HTML and RDF/XML, prefer HTML
2. Response: Okay, go to http://dbpedia.org/page/Switzerland
3. Request: I accept HTML and RDF/XML, prefer HTML
4. Response: Okay, I have an HTML representation

• curl -iLH "Accept: text/html" http://dbpedia.org/resource/Switzerland (requesting an HTML response)
• curl -iLH "Accept: text/html;q=0.9, application/rdf+xml;q=0.8" http://dbpedia.org/resource/Switzerland (preferring an HTML response)

• curl -iLH "Accept: application/rdf+xml" http://dbpedia.org/resource/Switzerland (requesting an RDF/XML response)
• rapper -i rdfxml http://dbpedia.org/resource/Switzerland

• A URI identifies (refers to or names) a web resource
• They are unique and essentially represents some thing (e.g., document, concept)
• IRI (Unicode/ISO 10646) is a generalization of URI (ASCII character set)

<scheme name> : <hierarchical part> [ ? <query> ] [ # <fragment> ]

More at: http://en.wikipedia.org/wiki/URI_scheme

See also RFC 2396

• http://www.ietf.org/rfc/rfc2396.txt
• http://en.wikipedia.org/wiki/Neuchâtel
• mailto:John.Doe@example.com
• ftp://ftp.is.co.za/rfc/rfc1808.txt
• ldap://[2001:db8::7]/c=GB?objectClass?one

• news:comp.infosystems.www.servers.unix
• irc://irc.freenode.net/csarven,isnick
• telnet://melvyl.ucop.edu/
• gopher://spinaltap.micro.umn.edu/00/Weather/California/Los%20Angeles
• urn:uuid:96550970-f26f-41f0-9dbd-db4c0d522889

• urn:isbn:9780812696110
• doi:10.1000/182
• bitcoin:1H67NnpSGAUrSRA5SkPHMmqNqHqpXHuFGp

• http://{lang}.wikipedia.org/wiki/{Article}
• http://dbpedia.org/resource/{Article}
• http://dbpedia.org/property/{id}
• https://twitter.com/{username}
• http://reddit.com/r/{subreddit}

• http://imgur.com/gallery/{hash}
• http://www.flickr.com/photos/{username}/{id}
• http://delicious.com/tag/{id}
• https://csarven.ca/#i
• http://worldbank.270a.info/dataset/{id}

• http://creativecommons.org/licenses/{type}/{version}/
• http://moodle.bfh.ch/course/view.php?id={id}
• http://www.wirtschaft.bfh.ch/{lang}/{degree}/{id}.html
• {firstname}.{lastname}@student.bfh.ch

• Dedicated service (1, 5, 100 years?)
• Consistent patterns
• Re-use existing identifiers
• Link multiple-representations

• Avoid ownership, versions (usually), auto-increment
• Avoid query strings, file extensions

A must read is TimBL's Cool URIs don't change

See also 10 Rules for Persistent URIs (see it as a rough guideline, not musts)

• Command-line analysis: Raptor utils, or curl
• Linked Data browsers (e.g., Tabulator)

“Any resource of significance should be given a URI.”

• Data is everywhere (personal, government, health, events..)
• Uncovering insights
• Predictions
• Making decisions (e.g., where to save energy)
• Smarter systems

Absolutely everything!

• Understanding human societies
• Health conditions
• Stable economies
• How do/should things work?

• Structured data available on a global scale
• Connect related data items across multiple sources
• ?
• Profit

• Classical data management vs. distributed Web
• Development using standards
• Open things up
• Gradual and sustainable

• Original data owners
• Data publishers
• Data enrichment parties
• Data consumers

• Essentially a language. A Graph model
• Similar to Entity-Attribute-Value (EAV) data model e.g., Sarven.height = 1.65m
• To describe concepts and their relationships (many graphs)
• Names for resources (URIs) e.g., https://csarven.ca/#i and http://dbpedia.org/property/height

How do we express ourselves?

• Sentences: subjects and predicates (verbs), and sometimes objects
• Body language meh ;)

• Decentralized invention (anyone can make theirs)
• Basics: RDF Syntax, RDF Schema
• Definitions for the relationship between things, or their classifications e.g.,Friend of a Friend (FOAF), Dublin Core Terms
• RDF Data Cube: Data structure definitions, code lists, datasets, ..
• SKOS: Code lists, and concepts can be reused

• SIOC: vocabulary for online communities
• Schema.org: various - Google/Bing/Yahoo/Yandex initiative
• Open Graph Protocol: webpages as part of rich objects in social graph - Facebook

• Meant to be an Ontology Language for the Web
• Very powerful: rich semantic meaning
• .. but it can also be painful (PITA)
• Need domain experts
• Usually need to write domain specific applications

<Subject> <Predicate> <Object> .

• Different ways to write it
• Serializations: RDFa, Turtle, N-Triples, RDF/XML
• Easy to - automatically - transform from one to another
• A triple statement: URI (spo), _:bnode (so), "literal" (o)

Sarven's height is 1.65m.

<https://csarven.ca/#i>
    <http://dbpedia.org/property/height>
        "1.65m" .

Bern is a city.

<http://dbpedia.org/resource/Bern>
    <http://www.w3.org/1999/02/22-rdf-syntax-ns#type>
        <http://dbpedia.org/ontology/City> .

Sarven is interested in electronic music and monkeys:

@prefix rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#> .
@prefix foaf: <http://xmlns.com/foaf/0.1/> .
@prefix wikipedia: <http://en.wikipedia.org/wiki/> .

<https://csarven.ca/#i>
    rdf:type foaf:Person ;
    foaf:givenName "Sarven"@en ;
    foaf:interest wikipedia:Electronica , wikipedia:Monkey ;
    foaf:mbox <mailto:info@csarven.ca> ;
    foaf:account <https://twitter.com/csarven> .

Switzerland has capital Bern. Bern is a City.

@prefix xsd: <http://www.w3.org/2001/XMLSchema#> .
@prefix dbr: <http://dbpedia.org/resource/> .
@prefix dbp: <http://dbpedia.org/property/> .
@prefix dbo: <http://dbpedia.org/ontology/> .
@prefix geo: <http://www.w3.org/2003/01/geo/wgs84_pos#> .

dbr:Switzerland dbp:capital dbr:Bern .
dbr:Bern
    rdf:type dbo:City  ;
    geo:lat "46.950001"^^xsd:float ;
    geo:long "7.439583"^^xsd:float .

<p about="https://csarven.ca/#i">
    Sarven is
    <span property="dbp:height">1.65m</span></p>

<p about="dbr:Bern">
   typeof="dbo:City">Bern is a city.</p>

<p about="https://csarven.ca/#i">
    Sarven is in <a rel="foaf:based_near"
                    href="dbr:Bern">Bern</a>.</p>

<rdf:RDF xmlns:rdf="
  http://www.w3.org/1999/02/22-rdf-syntax-ns#">
  <rdf:Description rdf:about="
    http://dbpedia.org/resource/Bern">
    <rdf:type rdf:resource="
      http://dbpedia.org/ontology/City">
  </rdf:Description>
</rdf:RDF>

<rdf:Description rdf:about="
  http://dbpedia.org/ontology/City">
  <rdf:type rdf:resource="
    http://www.w3.org/2002/07/owl#Class">
  <rdfs:label xml:lang="en">City</rdfs:label>
  <rdfs:label xml:lang="de">Stadt</rdfs:label>
</rdf:Description>

• Turtle: compact, human readable, triple pattern in SPARQL
• N-Triples: verbose, small footprint (inspection, processing), exchange
• RDF/XML: verbose, existing toolchains, tree model
• RDFa: (X)HTML page, for humans and machines
• JSON-LD: usually client-side dev, tree model

• A way to query for triple patterns (as opposed to searching)
• SPARQL endpoints (query public datasets)
• Federated queries (merge patterns from different source)
• See also: SPARQL 1.1 Query and SPARQL 1.1 Federated Query specifications.

Select a list of subjects that is a city.

SELECT ?city
WHERE {
    ?city a <http://dbpedia.org/ontology/City> .
}

People who were born in Bern before 1900:

PREFIX dbo: <http://dbpedia.org/ontology/>
PREFIX dbr: <http://dbpedia.org/resource/>
SELECT ?name ?birth ?person WHERE {
    ?person dbo:birthPlace dbr:Bern .
    ?person dbo:birthDate ?birth .
    ?person foaf:name ?name .
    FILTER (?birth < "1900-01-01"^^xsd:date) .
}
ORDER BY ?name

See results from DBpedia SPARQL Endpoint.

List of project names in countries which are classified to have low to middle income that are situated above the equator:

PREFIX skos: <http://www.w3.org/2004/02/skos/core#>
PREFIX wgs: <http://www.w3.org/2003/01/geo/wgs84_pos#>
PREFIX property: <http://worldbank.270a.info/property/>
PREFIX country: <http://worldbank.270a.info/classification/country/>

PREFIX income-level: <http://worldbank.270a.info/classification/income-level/>
PREFIX graph: <http://worldbank.270a.info/graph/>

SELECT ?projectLabel ?countryLabel WHERE {
  GRAPH graph:meta {
    ?country property:income-level income-level:LMC .
    ?country wgs:lat ?latitude .
    FILTER (?latitude > 0)
    ?country skos:prefLabel ?countryLabel . }

    GRAPH graph:world-bank-projects-and-operations {
        ?project property:country ?country ;
                 skos:prefLabel ?projectLabel . }
} ORDER BY ?projectLabel

See results at World Bank Linked Data SPARQL Endpoint.

CONSTRUCT { .. } WHERE {
{ SERVICE <http://data.linkedmdb.org/sparql> {
    SELECT * WHERE { .. }                    }
}
  UNION
{ SERVICE <http://dbpedia.org/sparql> {
    SELECT * WHERE { .. }             }
}

• Command-line analysis: Raptor utils, or curl
• SPARQL server and endpoint: Fuseki
• Query SPARQL endpoints: DBpedia, World Bank, .. many more, and the status of the ones in the LOD cloud.
• Linked Data browsers (e.g., Tabulator)

• Search for vocabularies in Linked Open Vocabularies (LOV)
• W3C validator
• See what's out there: LOD Cloud