Mapping Relational Databases to Linked Data

Mapping Relational Databases to Linked

DataBarry Norton (presenting)

Juan Sequeda

2

W3C RDB2RDF Standards

• Standards to map relational data to RDF

• A Direct Mapping of Relational Data to RDF– Default automatic mapping of relational data to

RDF

• R2RML: RDB to RDF Mapping Language– Customizable language to map relational data to

RDF

RDB2RDF

RDBDirect Mapping

RDF

automatic

Direct Mapping

RDB2RDF 3

PersonID

(pk)NAME AGE

1 Alice 25

2 Bob NULL

4RDB2RDF

Direct Mapping on Table

ID (pk)

NAME AGE

1 Alice 25

2 Bob NULL

Person

5RDB2RDF


ID (pk)

NAME AGE

1 Alice 25

2 Bob NULL

Person

<http://www.ex.com/Person/ID=1><http://www.ex.com/Person#NAME>

"Alice" .

6RDB2RDF


ID (pk)

NAME

AGECID(fk)

1 Alice 25 100

2 BobNULL

200

7RDB2RDF

PersonCID (pk)

TITLE

100Austin

200Madri

d

CityDM on Table Join

8RDB2RDF

ID (pk)

NAME

AGECID(fk)

1 Alice 25 100

2 BobNULL

200

PersonCID (pk)

TITLE

100Austin

200Madri

d

City

<http://www.ex.com/Person/ID=1><http://www.ex.com/Person#CID>

"100" .

DM on Table Join

ID (pk)

NAME

AGECID(fk)

1 Alice 25 100

2 BobNULL

200

PersonCID (pk)

TITLE

100Austin

200Madri

d

City

<http://www.ex.com/Person/ID=1><http://www.ex.com/Person#ref-CID>

<http://www.ex.com/City/CID=100>. 9RDB2RDF

<http://www.ex.com/Person/ID=1><http://www.ex.com/Person#CID>

"100" .

DM on Table Join

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DM Summary• Default and Automatic Mapping• URIs are automatically generated– <table>– <table#attribute>– <table#ref-attribute>– <Table#pkAttr=pkValue>

• RDF represents the same relational schema– Table Class– Attribute Property

RDB2RDF

RDB

RDF

R2RMLmanual

R2RML

11RDB2RDF

@prefix rr: <http://www.w3.org/ns/r2rml#> .@prefix foaf: <http://xmlns.com/foaf/0.1/> .@prefix ex: <http://example.com/> .@prefix xsd: <http://www.w3.org/2001/XMLSchema#> .@base <http://example.com/base/> .

<TriplesMap1> a rr:TriplesMap; rr:logicalTable [ rr:tableName "Person" ];

rr:subjectMap [ rr:template "http://ex/person{ID}"; rr:class foaf:Person ];

rr:predicateObjectMap [ rr:predicate foaf:name ; rr:objectMap [ rr:column "NAME" ] ] .

12RDB2RDF

R2RML Mapping

<http://www.ex.com/Person/ID=1>

<http://www.ex.com/Person#NAME>

<http://www.ex.com/data/person1>

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

‘Cool’ URIs

13RDB2RDF





SubjectURI

14RDB2RDF

URI Templates





PredicateURI

15RDB2RDF

Predicates



rr:subjectMap [ rr:template "http://ex/Person{ID}"; rr:class foaf:Person ];


Object Value

16RDB2RDF

Object Maps



rr:subjectMap [ rr:template "http://ex/Person{ID}"; rr:class foaf:Person];

rr:predicateObjectMap [ rr:predicate foaf:name ; rr:objectMap [ rr:column "NAME" ] ] . <subject uri> rdf:type foaf:Person

17RDB2RDF

Classes

<TriplesMap1> a rr:TriplesMap; rr:logicalTable [ rr:tableName"Person" ];

rr:subjectMap [ rr:template "http://ex/Person{ID}"; rr:class foaf:Person ];

rr:predicateObjectMap [ rr:predicate foaf:based_near ; rr:objectMap [

rr:parentTripleMap <TripleMap2>;rr:joinCondition [

rr:child "CID";rr:parent "CID"

]]

] .

<TriplesMap2> a rr:TriplesMap; rr:logicalTable [ rr:tableName "City" ];

rr:subjectMap [ rr:template "http://ex/City{CID}"; rr:class ex:City ];

rr:predicateObjectMap [ rr:predicate dc:title ; rr:objectMap [ rr:column "TITLE" ] ] .

18RDB2RDF

R2RML on Joins

SELECT gender, firstname, lastname FROM Person WHERE gender = "F"

ex:Person1 rdf:type ex:Woman .

ex:Person1 foaf:name "Alice Smith" .

Customized Mapping

19RDB2RDF


<TriplesMap1> a rr:TriplesMap; rr:logicalTable [ rr:sqlQuery

"""SELECT concat(firstname, " ", lastname) AS name

FROM Person WHERE gender = 'F' """];

rr:subjectMap [ rr:template "http://ex/Person{ID}"; rr:class ex:Woman];

rr:predicateObjectMap [ rr:predicate foaf:name ; rr:objectMap [ rr:column "name" ] ] .

20RDB2RDF

SQL Queries

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R2RML• Manual and Customizable• Learning Curve• View relational data as RDF expressed in the

structure and target vocabulary of the mapping author’s choice

RDB2RDF

RDB

RDF

Dump

SPARQL

Extract – Transform – Load (ETL)

22RDB2RDF

RDB

Mapping

SPARQL

Wrapper System

RDF

SQL

SQLResults

SPARQLResults 23RDB2RDF

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EUCLID Scenario

Visualization Module

Metadata

Streaming providers

Physical Wrapper

Downloads

Dat

a ac

quis

ition

R2R Transf.LD Wrapper

Musical Content

Appl

icati

on

Analysis & Mining Module

LD D

atas

etAc

cess

LD Wrapper

RDF/ XML

Integrated Dataset

Interlinking CleansingVocabulary Mapping

SPARQL Endpoint

Publishing

RDFa

Other content

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W3C RDB2RDF• Task: Integrate data from

relational DBMS with Linked Data

• Approach: map from relational schema to semantic vocabulary with R2RML

• Publishing: two alternatives –– Translate SPARQL into SQL on

the fly– Batch transform data into RDF,

index and provide SPARQL access in a triplestore

LD D

atas

etAc

cess

Integrated Data in

Triplestore

Interlinking CleansingVocabulary Mapping

SPARQL Endpoint

Publishing

Dat

a ac

quis

ition

R2RMLEngine

RelationalDBMS

RDB2RDF

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MusicBrainz Next Gen Schema

• artistAs pre-NGS, but

further attributes

• artist_creditAllows joint credit

• release_groupCf. ‘album’

versus:

• release• medium

• track• tracklist

• work• recording

https://wiki.musicbrainz.org/Next_Generation_Schema

RDB2RDF

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Music Ontology• MusicArtist– ArtistEvent, member_of

• SignalGroup ‘Album’ as per Release_Group

• Release– ReleaseEvent

• Record• Track• Work• Compositionhttp://musicontology.com/

RDB2RDF

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Scale• MusicBrainz RDF derived via R2RML:

lb:artist_member a rr:TriplesMap ; rr:logicalTable [rr:sqlQuery """SELECT a1.gid, a2.gid AS band FROM artist a1 INNER JOIN l_artist_artist ON a1.id = l_artist_artist.entity0 INNER JOIN link ON l_artist_artist.link = link.id INNER JOIN link_type ON link_type = link_type.id INNER JOIN artist a2 on l_artist_artist.entity1 = a2.id WHERE link_type.gid='5be4c609-9afa-4ea0-910b-12ffb71e3821'"""] ; rr:subjectMap [rr:template "http://musicbrainz.org/artist/{gid}#_"] ; rr:predicateObjectMap [rr:predicate mo:member_of ; rr:objectMap [rr:template "http://musicbrainz.org/artist/{band}#_" ; rr:termType rr:IRI]] .

300M Triples

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R2RML Class Mapping• Mapping tables to classes is ‘easy’:

lb:Artist a rr:TriplesMap ; rr:logicalTable [rr:tableName "artist"] ; rr:subjectMap [rr:class mo:MusicArtist ; rr:template

"http://musicbrainz.org/artist/{gid}#_"] ; rr:predicateObjectMap [rr:predicate mo:musicbrainz_guid ; rr:objectMap [rr:column "gid" ; rr:datatype xsd:string]] .

RDB2RDF

RDB2RDF 30

R2RML Property Mapping• Mapping columns to properties can be easy:

lb:artist_name a rr:TriplesMap ; rr:logicalTable [rr:sqlQuery """SELECT artist.gid, artist_name.name FROM artist INNER JOIN artist_name ON artist.name =

artist_name.id"""] ; rr:subjectMap [rr:template

"http://musicbrainz.org/artist/{gid}#_"] ; rr:predicateObjectMap [rr:predicate foaf:name ; rr:objectMap [rr:column "name"]] .

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NGS Advanced Relations

• Major entities (Artist, Release Group, Track, etc.) plus URL are paired(l_artist_artist)

• Each pairingof instancesrefers to a Link

• Links have types (cf. RDF properties)and attributes

http://wiki.musicbrainz.org/Advanced_Relationship

RDB2RDF

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Advanced Relations Mapping

• Mapping advanced relationships (SQL joins):lb:artist_member a rr:TriplesMap ; rr:logicalTable [rr:sqlQuery """SELECT a1.gid, a2.gid AS band FROM artist a1 INNER JOIN l_artist_artist ON a1.id = l_artist_artist.entity0 INNER JOIN link ON l_artist_artist.link = link.id INNER JOIN link_type ON link_type = link_type.id INNER JOIN artist a2 on l_artist_artist.entity1 = a2.id WHERE link_type.gid='5be4c609-9afa-4ea0-910b-

12ffb71e3821'"""] ; rr:subjectMap [rr:template

"http://musicbrainz.org/artist/{gid}#_"] ; rr:predicateObjectMap [rr:predicate mo:member_of ; rr:objectMap [rr:template

"http://musicbrainz.org/artist/{band}#_" ; rr:termType rr:IRI]] .

RDB2RDF

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Advanced Relations Mapping

• Mapping advanced relationships (SQL joins):lb:artist_dbpedia a rr:TriplesMap ; rr:logicalTable [rr:sqlQuery """SELECT artist.gid, REPLACE(REPLACE(url, 'wikipedia.org/wiki', 'dbpedia.org/resource'), 'http://en.', 'http://') AS url FROM artist INNER JOIN l_artist_url ON artist.id = l_artist_url.entity0 INNER JOIN link ON l_artist_url.link = link.id INNER JOIN link_type ON link_type = link_type.id INNER JOIN url on l_artist_url.entity1 = url.id WHERE link_type.gid='29651736-fa6d-48e4-aadc-a557c6add1cb' AND url SIMILAR TO 'http://(de|el|en|es|ko|pl|pt).wikipedia.org/wiki/%'"""] ; rr:subjectMap lb:sm_artist ; rr:predicateObjectMap [rr:predicate owl:sameAs ; rr:objectMap [rr:column "url"; rr:termType rr:IRI]] .

RDB2RDF

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SPARQL Example• SPARQL versus SQLASK {dbp:Paul_McCartney mo:member dbp:The_Beatles}

SELECT …

INNER JOININNER JOININNER JOININNER JOININNER JOININNER JOININNER JOININNER JOININNER JOININNER JOININNER JOININNER JOINWHERE AND … AND … AND … AND …

RDB2RDF

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For exercises, quiz and further material visit our website:

@euclid_project EUCLID project EUCLIDproject

http://www.euclid-project.eu

Other channels:

eBook Course

Mapping Relational Databases to Linked Data

Technology

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