RDF

Resource Description Framework: Information Representation in the Semantic Web

Tobias Pfeiffer, TESOBE
tobias@tesobe.com

Information

We make apps that deal with information.

Modelling Information

Entity Relationship Model

from http://wofford-ecs.org/dataandvisualization/ermodel/material.htm

Modelling Information
as Relational Data

Entities with Attributes

person
id	first_name	last_name
27	John	Doe	← an entity of type “person”
28	…	…

Relations

many2one

person
id	first_name	last_name	company_id
27	John	Doe	3
28	…	…	…

company
id	name
3	ACME Inc.
…	…

many2many

person
id	first_name	last_name
27	John	Doe
28	…	…

employment
person_id	company_id
27	3
…	…

company
id	name
3	ACME Inc.
4	…

one2many

person
id	first_name	last_name
27	John	Doe
28	…	…

company
id	name	person_id
3	ACME Inc.	27
4	…	…

Modelling Information
in RDF

The Resource Description Framework is a different way to express information.

Information as
Triple Data

Statements are Subject–Predicate–Object triples.

<http://people.org/John_Doe> <http://xmlns.com/foaf/0.1/knows> <http://people.org/Jane_Doe>

<http://people.org/John_Doe> <http://xmlns.com/foaf/0.1/image> <http://john.com/john.jpg>

<http://people.org/John_Doe> <http://xmlns.com/foaf/0.1/givenName> "John"

<http://people.org/John_Doe> <http://xmlns.com/foaf/0.1/age> 28^^xsd:integer

<http://people.org/John_Doe> <http://xmlns.com/foaf/0.1/name> "ジョンドウ"@ja

Different Notations I

N-Triples

<http://people.org/John_Doe> <http://xmlns.com/foaf/0.1/knows> <http://people.org/Jane_Doe>.

Turtle

@prefix ppl: <http://people.org/>
@prefix foaf: <http://xmlns.com/foaf/0.1/>

ppl:John_Doe foaf:givenName "John";
ppl:John_Doe foaf:familyName "Doe".

ppl:John_Doe foaf:knows ppl:Jane_Doe,
ppl:John_Doe foaf:knows <http://facebook.com/richard.miles>.

Different Notations II

RDF/XML

<?xml version="1.0" encoding="utf-8"?>
<rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
         xmlns:foaf="http://xmlns.com/foaf/0.1/">
  <rdf:Description rdf:about="http://people.org/John_Doe">
    <foaf:givenName>John</foaf:givenName>
    <foaf:knows rdf:resource="http://people.org/Jane_Doe" />
  </rdf:Description>
</rdf:RDF>

RDFa

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML+RDFa 1.0//EN"
    "http://www.w3.org/MarkUp/DTD/xhtml-rdfa-1.dtd">
<html xmlns="http://www.w3.org/1999/xhtml"
    xmlns:foaf="http://xmlns.com/foaf/0.1/"
    version="XHTML+RDFa 1.0" xml:lang="en">
  <head>
    <title>John's Home Page</title>
  </head>
  <body about="http://people.org/John_Doe">
    <h1>John's Home Page</h1>
    <p>My name is <span property="foaf:givenName">John</span> and I happen
      to know <a href="http://people.org/Jane_Doe" rel="foaf:knows">Jane</a>.
    </p>
  </body>
</html>

Information as a
Directed Graph

Querying for Information

Querying for Information
in RDBs

Query tables.

Hello from SQL

SELECT first_name
FROM person
WHERE last_name = 'Doe';

Result:

first_name (varchar)
John

Asking about relations

SELECT first_name, last_name, employer_id
FROM person
JOIN company ON (person.employer_id = company.id)
WHERE company.name = 'ACME Corp.';

Result:

first_name (varchar)	last_name (varchar)	employer_id (int)
John	Doe	3

Querying for Information
in RDF

Query graphs, not tables.

Hello from SPARQL

“All resources with last name ‘Doe’”

PREFIX foaf: <http://xmlns.com/foaf/0.1/>
SELECT ?person ?first_name
WHERE {
  ?person foaf:givenName ?first_name .
  ?person foaf:familyName "Doe" .
}

Result:

person
<http://people.org/John_Doe>
<http://people.org/Jane_Doe>

person	first_name
<http://people.org/John_Doe>	"John"
<http://people.org/Jane_Doe>	"Jane"

Asking About Relations

“All resources that are member of ‘ACME Corp.’”

PREFIX foaf: <http://xmlns.com/foaf/0.1/>

SELECT ?first_name ?last_name ?company
WHERE {
  ?person foaf:givenName ?first_name .
  ?person foaf:familyName ?last_name .
  ?company foaf:member ?person .
  ?company foaf:name "ACME Corp." .
}

Result:

first_name	last_name	company
"John"	"Doe"	<http://www.example.com/acme>
"Richard"	"Miles"	<http://www.example.com/acme>

Advanced Topics

PREFIX foaf: <http://xmlns.com/foaf/0.1/>
SELECT ?first_name ?last_name ?gender
WHERE {
  ?person foaf:givenName ?first_name .
  ?person foaf:familyName ?last_name .
  OPTIONAL { ?person foaf:gender ?gender } .
  ?person foaf:knows{1,2} ?employee .
  ?employee foaf:age ?age .
  ?company foaf:member ?employee .
  ?company foaf:name "ACME Corp." .
  FILTER (?age < 30)
}

Result:

first_name	last_name	gender
"Jane"	"Doe"	"female"
"Robby"	"Robot"

(plus: GROUP BY, HAVING, ORDER BY, subqueries, regex matching, …)

Storing Information

Storing Relational Data

Use a relational database ;-)

Storing RDF Data

Use a triple store.

RDB as a Backend

PREFIX foaf: <http://xmlns.com/foaf/0.1/>

SELECT ?first_name ?last_name ?company
WHERE {
  ?person foaf:givenName ?first_name .
  ?person foaf:familyName ?last_name .
  ?company foaf:member ?person .
  ?company foaf:name "ACME Corp." .
}

could map to

SELECT t1.obj, t2.obj, t4.obj
FROM data t1
JOIN data t2 ON (t1.sub = t2.sub)
JOIN data t3 ON (t3.obj = t1.sub)
JOIN data t4 ON (t4.sub = t3.sub)
WHERE t1.pred = 'foaf:givenName'
AND t2.pred = 'foaf:familyName'
AND t3.pred = 'foaf:member'
AND t4.pred = 'foaf:name'
AND t4.obj = 'ACME Corp.'

or to

SELECT givenName.obj, familyName.obj, name.obj
FROM givenName
JOIN familyName ON (givenName.sub = familyName.sub)
JOIN member ON (member.obj = givenName.sub)
JOIN name ON (name.sub = member.sub)
WHERE name.obj = 'ACME Corp.'

Selected Triple Stores

Name	Language	Website
Apache Jena	Java	jena.apache.org
→ implements a lot of SPARQL features
4store	C	www.4store.org
→ fast, small, robust
OpenLink Virtuoso	C	virtuoso.openlinksw.com
→ powers dbpedia, probably scales well ;-)
Sesame	Java	www.openrdf.org

Could be used directly in application
or with SPARQL via HTTP

Use Shared Information

How can we consume and extend other peoples’ data?

Using Shared
Relational Data

Data Sources

Open Data
Public SQL “endpoint”?
CSV files (e.g. Public WLAN hotspots in Berlin)
SQL dumps (e.g. Wikipedia Dumps)

Issues

Different names and meanings:

fname	lname
John	Doe

givenName	familyName	compId
John	Doe	4

name	company
John Doe	ACME Corp.

Encodings
Naming conflicts
Duplicate information
Merging issues
Missing documentation
…

Using Shared RDF Data

Data Sources

dbpedia: an RDF version of Wikipedia

SELECT ?personName ?langName WHERE {
  ?person dbpedia-owl:knownFor ?language .
  ?language rdf:type dbpedia-owl:ProgrammingLanguage .
  ?language dbpprop:year ?year .
  ?person rdfs:label ?personName .
  ?language rdfs:label ?langName .
  FILTER(LANG(?personName) = 'en' && LANG(?langName) = 'en')
} ORDER BY DESC(?year) LIMIT 3

personName	langName
"Donald D. Chamberlin"@en	"XQuery"@en
"Patrick Collison"@en	"Croma"@en
"Martin Odersky"@en	"Scala (programming language)"@en

Linked Open Data

Import vs. Online Access

Often RDF dumps and SPARQL endpoints are provided.

Import

+ offline access (import into its own “graph”)
+ always available
– large mass of data
– admin work necessary

Online Access

+ add new data sources quickly
+ less server resources necessary
– SPARQL endpoint may be down/slow
– data may change/disappear

Federated Queries

Automatic federation is a current research topic, cf. DARQ (dead), SQUIN, FedX.
Manual federation via SERVICE keyword.

PREFIX foaf:   
SELECT ?name
WHERE
{
  <http://people.org/John_Doe> foaf:knows ?person .
  SERVICE <http://people.example.org/sparql> {
    ?person foaf:name ?name .
  }
}

Federated Queries:
Architecture Proposal

Architecture for federated SPARQL queries

RDF

Resource Description Framework: Information Representation in the Semantic Web

Information

Modelling Information

Entity Relationship Model

Modelling Informationas Relational Data

Entities with Attributes

Relations

many2one

many2many

one2many

Modelling Information in RDF

Information as Triple Data

Different Notations I

N-Triples

Turtle

Different Notations II

RDF/XML

RDFa

Information as a Directed Graph

Querying for Information

Querying for Information in RDBs

Hello from SQL

Asking about relations

Querying for Information in RDF

Hello from SPARQL

Asking About Relations

Advanced Topics

Storing Information

Storing Relational Data

Storing RDF Data

RDB as a Backend

Selected Triple Stores

Use Shared Information

Using Shared Relational Data

Data Sources

Issues

Using Shared RDF Data

Data Sources

Import vs. Online Access

Import

Online Access

Federated Queries

Federated Queries:Architecture Proposal

Conclusion

Things I didn’t talk about

Thank You!

Modelling Information
as Relational Data

Modelling Information
in RDF

Information as
Triple Data

Information as a
Directed Graph

Querying for Information
in RDBs

Querying for Information
in RDF

Using Shared
Relational Data

Federated Queries:
Architecture Proposal