What?
A simple guide usable by any Ruby developer seeking to exploit SPARQL without hassles.
Why?
SPARQL is a powerful query language, results serialization
format, and an HTTP based data access protocol from
the W3C. It provides a mechanism for accessing and integrating data
across Deductive Database Systems (colloquially
referred to as triple or quad stores in Semantic Web and Linked Data circles) -- database systems
(or data spaces) that manage proposition oriented records in
3-tuple (triples) or 4-tuple (quads) form.
How?
SPARQL queries are actually HTTP payloads (typically). Thus,
using a RESTful client-server interaction pattern, you can dispatch
calls to a SPARQL compliant data server and receive a payload for
local processing e.g. local object binding re. Ruby.
Steps:
- From your command line execute: aptitude search '^ruby', to
verify Ruby is in place
- Determine which SPARQL endpoint you want to access e.g.
DBpedia or a local Virtuoso instance (typically:
http://localhost:8890/sparql).
- If using Virtuoso, and you want to populate its quad store
using SPARQL, assign "SPARQL_SPONGE" privileges to user
"SPARQL" (this is basic control, more sophisticated WebID based
ACLs are available for controlling SPARQL access).
Script:
#!/usr/bin/env ruby
#
# Demonstrating use of a single query to populate a # Virtuoso Quad Store.
#
require 'net/http'
require 'cgi'
require 'csv'
#
# We opt for CSV based output since handling this format is straightforward in Ruby, by default.
# HTTP URL is constructed accordingly with CSV as query results format in mind.
def sparqlQuery(query, baseURL, format="text/csv")
params={
"default-graph" => "",
"should-sponge" => "soft",
"query" => query,
"debug" => "on",
"timeout" => "",
"format" => format,
"save" => "display",
"fname" => ""
}
querypart=""
params.each { |k,v|
querypart+="#{k}=#{CGI.escape(v)}&"
}
sparqlURL=baseURL+"?#{querypart}"
response = Net::HTTP.get_response(URI.parse(sparqlURL))
return CSV::parse(response.body)
end
# Setting Data Source Name (DSN)
dsn="http://dbpedia.org/resource/DBpedia"
#Virtuoso pragmas for instructing SPARQL engine to perform an HTTP GET
#using the IRI in FROM clause as Data Source URL
query="DEFINE get:soft \"replace\"
SELECT DISTINCT * FROM <#{dsn}> WHERE {?s ?p ?o} "
#Assume use of local installation of Virtuoso
#otherwise you can change URL to that of a public endpoint
#for example DBpedia: http://dbpedia.org/sparql
data=sparqlQuery(query, "http://localhost:8890/sparql/")
puts "Got data:"
p data
#
# End
Output
Got data:
[["s", "p", "o"],
["http://dbpedia.org/resource/DBpedia",
"http://www.w3.org/1999/02/22-rdf-syntax-ns#type",
"http://www.w3.org/2002/07/owl#Thing"],
["http://dbpedia.org/resource/DBpedia",
"http://www.w3.org/1999/02/22-rdf-syntax-ns#type",
"http://dbpedia.org/ontology/Work"],
["http://dbpedia.org/resource/DBpedia",
"http://www.w3.org/1999/02/22-rdf-syntax-ns#type",
"http://dbpedia.org/class/yago/Software106566077"],
...
Conclusion
CSV was chosen over XML (re. output
format) since this is about a "no-brainer installation and
utilization" guide for a Ruby developer that already knows how to
use Ruby for HTTP based data access. SPARQL just provides an added
bonus to URL dexterity (delivered via URI abstraction) with regards
to constructing Data Source Names or Addresses.
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