This document discusses three main ways to access remote Linked Data: 1) making HTTP requests to resource URIs, 2) using SPARQL queries, and 3) getting a local copy of a dataset. It then provides more details on each method, including making HTTP requests to retrieve RDF data, examples of SPARQL queries to endpoints, and getting local copies through SPARQL constructs, crawling, or direct downloads. The document also lists several RDF libraries and provides a hands-on example of a SPARQL query.

1. QUERYING Linked Data

2. 1. Three main ways of accessing
remote Linked Data
1. Through HTTP request on the resource URI
2. Through SPARQL queries
3. Get a copy of a dataset

3. 1. Through HTTP request on the
resource URI
• HTTP GET on resource, parse, follow links
– Simple HTTP requests and RDF parsing
– Requires dereferencable URIs
– One request per resource: may require many
requests
• Local caching can be done
• Crawling GET /resource/Amsterdam HTTP/1.1
Host: dbpedia.org
Accept: text/html;q=0.5, application/rdf+xml
I’m ok with HTML… …but I really prefer RDF

4. • With CURL
– curl -L -H "Accept: application/rdf+xml"
http://dbpedia.org/resource/Madrid
– curl -L -H "Accept: text/turtle"
http://dbpedia.org/resource/Madrid
– curl -L -H "Accept: text/turtle"
http://purl.org/collections/nl/dss/das/voyage-5580_1
• With Sindice inspector (or other tool)
• http://inspector.sindice.com/inspect?url=
• http://inspector.sindice.com/inspect?url=http://dbpedia.or
g/resource/Madrid

5. 2. Through SPARQL queries
• Full-blown query language
• Needs SPARQL endpoint
$query =
"SELECT distinct ?title ?description WHERE {
?x <http://data.open.ac.uk/podcast/ontology/relatesToCourse>
<http://data.open.ac.uk/course/t209>.
?x <http://purl.org/dc/terms/title> ?title.
?x <http://www.w3.org/TR/2010/WD-mediaont-10-20100608/description> ?description }
LIMIT 10
";
$requestURL = 'http://data.open.ac.uk/query?query='.urlencode($query);
$response = request($requestURL);
SPARQL in PHP example
http://www.greenhughes.com/content/approach-consuming-linked-data-php

6. 3. Get a local copy of a dataset
• through SPARQL CONSTRUCT,
• crawling or
• Direct file download
• Save in triple store
– or convert to something else

7. RDF Libraries
Redland: http://www.librdf.org/ Perl, Python,
PHP, Ruby, C#, Objective-C
Jena: http://jena.sourceforge.net/ Java
RDFLib: http://www.rdflib.net/ Python
ARC2: http://arc2.semsol.net/ PHP
ActiveRDF: http://www.activerdf.org/ Ruby

8. Handson with SPARQL

9. SPARQL
A Query-language for the Web of
Data

10. SPARQL – Querying the Web of Data
• query language for RDF graphs (i.e., linked
data)
• extract specific information out of a dataset
(or several datasets)
• "The SQL for the Web of Data"

11. SPARQL Endpoint
Reasoning?

12. PREFIX mo: <http://purl.org/ontology/mo/>
PREFIX dce: <http://purl.org/dc/elements/1.1/>
PREFIX xsd: <http://www.w3.org/2001/XMLSchema#>
SELECT DISTINCT ?album ?title ?release_date
WHERE {
?album a mo:Record ;
dce:date ?release_date ;
dce:title ?title .
FILTER (year(?release_date) = 2007 &&
month(?release_date) = 7)
}
ORDER BY ?release_date

13. SPARQL in a Nutshell

14. PREFIX mo: <http://purl.org/ontology/mo/>
PREFIX dce: <http://purl.org/dc/elements/1.1/>
PREFIX xsd: <http://www.w3.org/2001/XMLSchema#>
SELECT DISTINCT ?album ?title ?release_date
WHERE {
?album a mo:Record ;
dce:date ?release_date ;
dce:title ?title .
FILTER (year(?release_date) = 2007 &&
month(?release_date) = 7)
}
ORDER BY ?release_date
graph pattern

15. Lets try it ourselves
http://tinyurl.com/getafesparql