Generating Linked Open Data from  
heterogeneous Open Data sources with 
Anastasia Dimou 
 
anastasia.dimou@ugent.be 
@natadimou 
Ghent University – iMinds – Multimedia Lab 
rml.io 
 Semantic Web enabled applications 
rely on data represented as  
Linked Open Data 
semantically annotated  
 using ontologies and vocabularies 
 
 
 Most of the data that we would like to  
be able to query as Linked Open Data 
 
exists in formats other than RDF 
 
 
12% of webpages contain any structured data 
such as microformat, microdata and RDFa 
 
derived from 6% of all websites 
There are… 
 
over 11,000 APIs according to 
ProgrammableWeb.org  
 
only 74 return results in RDF 
 
But more than 5000  
return results in JSON or XML 
 LOD enables SW apps 
 
 
SW apps demands LOD 
Semantic Web 
Linked Open Data 
Open Data 
Many  
languages, tools and approaches 
were proposed  
 
to convert data  
from different data sources to RDF 
Existing mapping solutions map  
per-format and per-source 
  focus more on handling the source 
      rather than modeling the domain 
 
OR 
 
provide case-specific solutions  
  better model the domain 
 
 
 
R2RML mappings R2RML processor 
Data OWNER / PUBLISHER 
defines 
RDF 
DB CSV JSON XML 
RDF RDF RDF 
The mappings are… 
 
independently defined disregarding  
possible prior definitions  
links to other resources 
(re)using same ontologies for similar data 
 
manually aligned/interlinked 
by reconstructing the same URIs 
by post-mapping interlinking 
A well-considered policy is required 
when mapping data to RDF  
in the context of a certain knowledge domain 
that shifts the focus  
 
FROM modeling the data of a source 
 
TO modeling the domain-level knowledge  
using the available data source(s) 
uniform mapping definitions  
    to describe mapping rules for heterogeneous sources  
 
interoperable mapping definitions 
    that would allow the re-use of mapping rules 
    across different implementations 
 
reusable mapping definitions  
    that would allow the re-use of mapping rules  
    for representing data in the same or different formats  
R2RML mappings R2RML processor 
Data OWNER / PUBLISHER 
defines 
RDF 
DB CSV JSON XML 
RDF RDF RDF 
Mappings definitions processor 
Data OWNER / PUBLISHER 
defines 
RDF 
DB CSV JSON XML 
 
 
RDF Mapping Language (RML) 
 
generic scalable mapping language 
for mapping heterogeneous data into RDF 
in an integrable and interoperable fashion 
 
superset of the W3C recommended 
R2RML mapping language 
 
http://rml.io 
 
RDF Mapping Language 
RML.io  
 
RDF Mapping Language (RML) 
Source 
Triples Map 
Logical Source 
Subject Map 
Predicate-Object  
Map 
Predicate 
Map 
Object Map 
Term 
Map 
template 
constant 
reference 
Iterator 
Reference 
Formulation 
Referencing 
Object Map 
Triples 
Map 
Join 
Condition 
Parent 
column 
Child 
column 
 
RDF Mapping Language 
RML  
 
 
RML generating triples 
RML reusing mappings 
RML aligning & interlinking 
 
RDF Mapping Language (RML) 
<subject>  <predicate> <object> 
<http://ex.com/Anastasia%20Dimou>       a        ex:Person . 
<http://ex.com/Charalampos%20Bratsas> a        ex:Person . 
RDF Mapping Language (RML) 
Triples Map Subject Map 
Predicate-Object  
Map 
Predicate 
Map 
Object Map 
Term 
Map 
template 
constant 
reference 
RDF Term :  
a URI  
a literal  
a blank node 
<subject>  <predicate> <object> 
RML subject 
Triples Map 
Subject Map 
NAME BIRTH_DATE DEATH_DATE 
Robert Theodore McCall 1919-12-23 2010-02-26 
Ronald Anderson 1929-12-06 
<#ArtistMapping> 
  
    rr:subjectMap [ 
     rr:template “http://ex.com/{NAME}” ; 
     rr:class ex:Person ]; 
<http://ex.com/Robert%20Theodore%20McCall>  a      ex:Person 
RML predicate & object 
Predicate Map 
NAME BIRTH_DATE DEATH_DATE 
Robert Theodore McCall 1919-12-23 2010-02-26 
Ronald Anderson 1929-12-06 
<#ArtistMapping> 
    rr:predicateObjectMap [ 
         
     rr:predicate ex:birth_date;     
         
     rr:objectMap [  
            rr:column "BIRTH_DATE" ]  ]; 
<http://ex.com/Robert%20Theodore%20McCall>  ex:birth_date  “1919-12-23” 
Predicate Object Map 
Object Map 
Triples Map 
[ ... … 
{ "Title": "Apollo 11 Crew", 
"Artist": "Ronald Anderson", 
"Ref": "NPG_70_36", 
"Sitter": [ 
 { "Name": "Neil Armstrong", 
   "Birth Date": "1930-08-05" }, 
{ "Name": "Buzz Aldrin", 
  "Birth Date": "1930-01-20" }, 
{ "Name": "Michael Collins" } ], 
"DateOfWork": "1969" }, 
{ "Title": "Neil Armstrong", 
"Artist": "Robert Theodore McCall", 
"Ref": "S_NPG_2010_51", 
"Sitter": [ 
 { "Name": "Neil Armstrong" } ], 
"DateOfWork": "2009" },  
... … ] 
<Artists> ... ... 
<Artist> 
<Name>Robert Theodore McCall</Name> 
<Birth_Date>1919-12-23</Birth_Date> 
<Death_Date>2010-02-26</Death_Date> 
</Artist> 
<Artist> 
<Name>Ronald Anderson</Name> 
<Birth_Date>1929-12-06</Birth_Date> 
<Death_Date/> 
</Artist> ... ... 
</Artists> 
 
artworks.JSON artists.XML 
<#ArtworkMapping> 
      rml:logicalSource 
  
  [ rml:source “http://ex.com/artworks.json” ; 
     
    rml:referenceFormulation ql:JSONPath ]. 
Triples Map 
Logical Source 
source 
<#ArtistMapping> 
  rml:logicalSource   
   
  [ rml:source “artists.xml”; 
    
    rml:referenceFormulation ql:XPath ]. Reference Formulation 
Triples Map 
Logical Source 
source 
Reference Formulation 
[ ... … 
{ "Title": "Apollo 11 Crew", 
"Artist": "Ronald Anderson", 
"Ref": "NPG_70_36", 
"Sitter": [ 
 { "Name": "Neil Armstrong", 
   "Birth Date": "1930-08-05" }, 
{ "Name": "Buzz Aldrin", 
  "Birth Date": "1930-01-20" }, 
{ "Name": "Michael Collins" } ], 
"DateOfWork": "1969" }, 
{ "Title": "Neil Armstrong", 
"Artist": "Robert Theodore McCall", 
"Ref": "S_NPG_2010_51", 
"Sitter": [ 
 { "Name": "Neil Armstrong" } ], 
"DateOfWork": "2009" },  
... … ] 
<#ArtworkMapping> 
      rml:logicalSource 
  
  [ rml:source “http://ex.com/artworks.json” ; 
    rml:rererenceFormulation ql:JSONPath ; 
    rml:iterator “$.[*]” ]. 
<#SitterMapping> 
      rml:logicalSource 
  [ rml:source “http://ex.com/artworks.json”; 
    rml:rererenceFormulation ql:JSONPath ; 
    rml:iterator “$.[*].Sitter” ]. 
<#ArtistMapping> 
rml:logicalSource 
    [ rml:source “http://ex.com/artists.xml”; 
      rml:rererenceFormulation ql:XPath ; 
      rml:iterator “/Artists/Artist” ] ; 
 
 rr:subjectMap [ 
    rr:template “http://ex.com/{Name}” ]; 
 
  rr:predicateObjectMap [ 
     rr:predicate ex:death_date ; 
     rr:objectMap [ 
         rml:reference 
              “/Artists/Artist/Death_Date”] ]. 
<Artists> ... ... 
<Artist> 
<Name>Robert Theodore McCall</Name> 
<Birth_Date>1919-12-23</Birth_Date> 
<Death_Date>2010-02-26</Death_Date> 
</Artist> 
<Artist> 
<Name>Ronald Anderson</Name> 
<Birth_Date>1929-12-06</Birth_Date> 
<Death_Date/> 
</Artist> ... ... 
</Artists> 
 
<http://ex.com/Robert+Theodore+McCall>  
 ex:death_date “1929-12-06”. 
 
RDF Mapping Language 
RML  
 
 
RML generating triples 
RML reusing mappings 
RML aligning & interlinking 
 
 
Avoid… 
 
redefining and replicating URI patterns  
 
remodeling the same domain 
 
 
Uniquely define the URI patterns that  
generates a resource and refer to its definition 
 
{ ... "Performance" : 
  { "Perf_ID": "567", 
    "Location": {  
      "lat": "51.043611" , 
      "long": "3.717222” } },  
... } 
 
 
 
<Events> ... 
  <Exhibition id="398"> 
    <Location> 
      <lat>51.076891</lat> 
      <long>3.717222</long> 
    </Location> 
  </Exhibition> ... 
</Events> 
<#PerformancesMapping> 
  rr:subjectMap [  
     rr:template “http://ex.com/{Perf_ID}”]; 
  
 rr:predicateObjectMap [  
   rr:predicate ex:location; 
   rr:objectMap [  
     rr:parentTriplesMap <#LocationMapping> ] ]. 
<#EventsMapping> 
  rr:subjectMap [  
    rr:template "http://ex.com/{@id}" ]; 
   
rr:predicateObjectMap [  
    rr:predicate ex:location; 
    rr:objectMap [  
      rr:parentTriplesMap <#LocationMapping>]]. 
 
{ ... "Performance" : 
  { "Perf_ID": "567", 
    "Location": {  
      "lat": "51.043611" , 
      "long": "3.717222” } },  
... } 
 
 
 
<Events> ... 
  <Exhibition id="398"> 
    <Location> 
      <lat>51.076891</lat> 
      <long>3.717222</long> 
    </Location> 
  </Exhibition> ... ... 
</Events> 
<#LocationMapping> 
  rr:subjectMap [  
    rr:template "http://ex.com/{lat},{long}"]; 
 
  rr:predicateObjectMap [  
    rr:predicate ex:long; 
    rr:objectMap [ rml:reference "long" ] ]; 
 
  rr:predicateObjectMap [  
    rr:predicate ex:lat; 
    rr:objectMap [ rml:reference "lat" ] ] . 
ex:51.043611, 3.717222 
   ex:lat “3.717222”,   ex:long “51.043611”. 
 
ex:51.076891, 3.717222 
   ex:lat “3.717222”,   ex:long “51.043611”. 
 
RDF Mapping Language 
RML  
 
 
RML generating triples 
RML reusing mappings 
RML aligning & interlinking 
 
{ ...  
"Performance" : 
  { "Perf_ID": "567", 
    "Venue": {  
      "Name": "STAM", 
      "Venue_ID": "78" }, 
    "Location": {  
      "long": "3.717222", 
      "lat": "51.043611" } } ,  
... } 
 
 
 
 
 
 
 
ex:567 ex:venue ex:78 
<#PerformancesMapping> 
 rr:subjectMap [  
   rr:template “http://ex.com/{Perf_ID}”]; 
 
   rr:predicateObjectMap [  
     rr:predicate ex:venue; 
     rr:objectMap [  
       rr:parentTriplesMap <#VenueMapping> ] ]. 
<#VenueMapping> 
  rml:logicalSource [ 
    rml:source "http://ex.com/performances.json"; 
    rml:referenceFormulation ql:JSONPath; 
    rml:iterator "$.Performance.Venue.[*]" ]; 
     
rr:subjectMap [  
      rr:template "http://ex.com/{Venue_ID}"; 
      rr:class ex:Venue ]. 
{ ... "Performance" : 
  { "Perf_ID": "567", 
    "Venue": {  
    "Name": "STAM", 
    "Venue_ID": "78" },  
... } 
 
 
<Events> ... 
  <Exhibition id="398"> 
    <Venue>STAM</Venue> 
  </Exhibition> ... ... 
</Events> 
 
ex:567 ex:venue ex:78. 
ex:398 ex:venue ex:78. 
<#EventsMapping> 
  rr:subjectMap [  
    rr:template "http://ex.com/{@id}" ]; 
 
  rr:predicateObjectMap [  
    rr:predicate ex:venue; 
    rr:objectMap [  
      rr:parentTriplesMap <#VenueMapping>; 
        rr:joinCondition [ 
          rr:child "$.Performance.Venue.Name"; 
          rr:parent "/Events/Exhibition/Venue" ] 
] ] . 
 
ex:567 ex:venue ex:78. 
ex:398 ex:venue ex:STAM. 
ex:78 owl:sameAs ex:STAM 
 
RDF Mapping Language 
(RML)  
 
Processing  
 
 
Extraction Module Mapping Module 
RML Processor 
rml.io 
Anastasia Dimou  
 
@natadimou  
anastasia.dimou@ugent.be