Let's get to SPARQL

SPARQL is really exciting query language for RDF

• pronounced "sparkle"
• SPARQL Protocol and RDF Query Language
• On 15 January 2008, SPARQL became an official W3C Recommendation
• allows one to perform complex joins of disparate databases in a single, simple query
• query for triple patterns using conjunction, disjunction, and optional patterns

SPARQL implementations

There are SPARQL implementations for most popular programming languages

• Redland's Rasqal (C with bindings for Perl, Python, Ruby, PHP and others)
• Jena's ARQ (Java)
• RDFLib (Python)
• and many others

SPARQL store implementations

Even better there are several open-source scalable RDF stores that support SPARQL

• Openlink's Virtuoso
• Garlik's 4Store
• Jena-based Joseki
• D2R Server
• and others

A simple SPARQL query example

SPARQL syntax is a relatively intuitive mashup of traditional SQL and Turtle

		
SELECT ?foo ?bar 
  WHERE { <http://dbpedia.org/resource/Bill_Evans> ?foo ?bar . }

this will return all triples in the store with Bill Evans as the subject

terms beginning with ? are universally quantified variables

SPARQL - basic syntax

• Prefix declarations, for abbreviating URIs
• Dataset definition, stating what RDF graph(s) are being queried
• A result clause, identifying what information to return from the query
• The query pattern, specifying what to query for in the underlying dataset
• Query modifiers, slicing, ordering, and otherwise rearranging query results

SPARQL - basic syntax

# prefix declarations
PREFIX foo: <http://example.com/resources/>
...
# dataset definition
FROM ...
# result clause
SELECT ...
# query pattern

WHERE {
    ...
}
# query modifiers
ORDER BY ...

SPARQL query example

as in Turtle we can use the keyword PREFIX

PREFIX dbpedia: <http://dbpedia.org/resource/Bill_Evans>
SELECT ?p ?o 
  WHERE { dbpedia:Bill_Evans ?p ?o . }

notice we don't need the @ and . around the PREFIX keyword

Challenge

Challenge answer

Note there is more than one way to get this answer

	PREFIX dbpo: <http://dbpedia.org/ontology/>
	PREFIX dbpp: <http://dbpedia.org/property/>
	PREFIX : <http://dbpedia.org/resource/>


	SELECT *
	WHERE { 
	?artist a dbpo:MusicalArtist ;
	    dbpo:genre :Jazz ;
	    dbpp:instrument :Piano ;
	    dbpo:homeTown :New_Jersey.
	}
	

A quick note on Python

We can make SPARQL queries against endpoints in Python with SPARQLWrapper

	$ sudo easy_install SPARQLWrapper
	

a quick example of syntax

from SPARQLWrapper import SPARQLWrapper2
sparql = SPARQLWrapper2('http://dbpedia.org/sparql')
query = 'SELECT * WHERE { ?s ?p ?o } LIMIT 20'
sparql.setQuery(query)
response = sparql.query()
for binding in response.bindings:
	print binding['s'].value
	print binding['p'].value
	print binding['o'].value

Detailed examples

There are detailed examples of how to use SPARQLWrapper in the github repository

Using SPARQLWrapper and RDFLib to build a Jamendo artist recommender:

http://github.com/kurtjx/MatWoD/blob/master/examples/scripts/recommend_by_location/

Also some examples using Ruby

"Find all music artists from Detroit":

http://github.com/kurtjx/MatWoD/blob/master/examples/scripts/artists_based_in_detroit/

Warning!

In your handout - there are two example queries

the second query uses blank nodes [] and a UNION statement to select all the properties and classes contained in an endpoint

while this is a valid query, it will cause most endpoints to choke because it is very expensive - better to break into two separate queries with limits

	SELECT DISTINCT ?type 
	WHERE { [] a ?type . } LIMIT 10	
	

	SELECT DISTINCT ?prop
	WHERE {} [] ?prop [] . } LIMIT 10