SPARQL for RDF.rb

This is a Ruby implementation of SPARQL for RDF.rb.

Features

• 100% free and unencumbered public domain software.
• SPARQL 1.1 Query parsing and execution (excluding Property Paths)
• SPARQL results as XML, JSON, CSV, TSV or HTML.
• SPARQL CONSTRUCT or DESCRIBE serialized based on Format, Extension of Mime Type using available RDF Writers (see Linked Data)
• SPARQL Client for accessing remote SPARQL endpoints.
• Rack and Sinatra middleware to perform HTTP content negotiation for result formats
  • Compatible with any Rack or Sinatra application and any Rack-based framework.
  • Helper method for describing SPARQL Service Description
• Compatible with Ruby >= 1.9.2.
• Compatible with older Ruby versions with the help of the Backports gem.
• Supports Unicode query strings both on all versions of Ruby.

Description

The {SPARQL} gem implements SPARQL 1.1 Query, and provides Rack and Sinatra middleware to provide results using HTTP Content Negotiation.

• {SPARQL::Grammar} implements a SPARQL 1.1 Query parser generating SPARQL S-Expressions (SSE).
  • Support for Property Paths is excluded. See the section on SPARQL 1.1 Query extensions and limitations for further detail.
• {SPARQL::Algebra} executes SSE against Any RDF::Graph or RDF::Repository, including compliant RDF.rb repository adaptors such as RDF::DO and RDF::Mongo.
• {Rack::SPARQL} and {Sinatra::SPARQL} provide middleware components to format results using an appropriate format based on HTTP content negotiation.

SPARQL 1.1 Query Extensions and Limitations

The {SPARQL} gem uses the SPARQL 1.1 Query {file:etc/sparql11.bnf EBNF grammar}, which provides much more capability than SPARQL 1.0, but has a few limitations:

• The format for decimal datatypes has changed in RDF 1.1; they may no longer have a trailing ".", although they do not need a leading digit.
• BNodes may now include extended characters, including ".".

The SPARQL gem now implements the following SPARQL 1.1 Query operations:

• Functions
• BIND
• GROUP BY
• Aggregates
• Subqueries
• Inline Data
• Inline Data
• Exists
• Negation

The only major area of SPARQL 1.1 Query missing is Property Paths, which will be in later release along with:

• Update,
• Federated Query,
• Entailment Regimes,
• Protocol, and
• Graph Store HTTP Protocol

either in this, or related gems.

Updates for RDF 1.1

Starting with version 1.1.2, the SPARQL gem uses the 1.1 version of the RDF.rb, which adheres to RDF 1.1 Concepts rather than RDF 1.0. The main difference is that there is now no difference between a Simple Literal (a literal with no datatype or language) and a Literal with datatype xsd:string; this causes some minor differences in the way in which queries are understood, and when expecting different results.

Additionally, queries now take a block, or return an Enumerator; this is in keeping with much of the behavior of RDF.rb methods, including Queryable#query, and with version 1.1 or RDF.rb, Query#execute. As a consequence, all queries which used to be of the form query.execute(repository) may equally be called as repository.query(query). Previously, results were returned as a concrete class implementing RDF::Queryable or RDF::Query::Solutions, these are now Enumerators.

SPARQL Extension Functions

Extension functions may be defined, which will be invoked during query evaluation. For example:

# Register a function using the IRI <http://rubygems.org/gems/sparql#crypt>
crypt_iri = RDF::URI("http://rubygems.org/gems/sparql#crypt")
SPARQL::Algebra::Expression.register_extension(crypt_iri) do |literal|
  raise TypeError, "argument must be a literal" unless literal.literal?
  RDF::Literal(literal.to_s.crypt)
end

Then, use the function in a query:

PREFIX rsp: <http://rubygems.org/gems/sparql#>
PREFIX schema: <http://schema.org/>
SELECT ?crypted
{
  [ schema:email ?email]
  BIND(rsp:crypt(?email) AS ?crypted)
}

See {SPARQL::Algebra::Expression.register_extension} for details.

Middleware

{Rack::SPARQL} is a superset of Rack::LinkedData to allow content negotiated results to be returned any RDF::Enumerable or an enumerator extended with RDF::Query::Solutions compatible results. You would typically return an instance of RDF::Graph, RDF::Repository or an enumerator extended with RDF::Query::Solutions from your Rack application, and let the Rack::SPARQL::ContentNegotiation middleware take care of serializing your response into whatever format the HTTP client requested and understands.

{Sinatra::SPARQL} is a thin Sinatra-specific wrapper around the {Rack::SPARQL} middleware, which implements SPARQL content negotiation for Rack applications. {Sinatra::SPARQL} also supports SPARQL 1.1 Service Description.

The middleware queries RDF.rb for the MIME content types of known RDF serialization formats, so it will work with whatever serialization extensions that are currently available for RDF.rb. (At present, this includes support for N-Triples, N-Quads, Turtle, RDF/XML, RDF/JSON, JSON-LD, RDFa, TriG and TriX.)

Remote datasets

A SPARQL query containing FROM or FROM NAMED will load the referenced IRI unless the repository already contains a context with that same IRI. This is performed using RDF.rb RDF::Util::File.open_file passing HTTP Accept headers for various available RDF formats. For best results, require Linked Data to enable a full set of RDF formats in the GET request. Also, consider overriding RDF::Util::File.open_file with an implementation with support for HTTP Get headers (such as Net::HTTP).

Queries using datasets are re-written to use the identified graphs for FROM and FROM NAMED by filtering the results, allowing the use of a repository that contains many graphs without confusing information.

Result formats

SPARQL.serialize_results may be used on it's own, or in conjunction with {Rack::SPARQL} or {Sinatra::SPARQL} to provide content-negotiated query results. For basic SELECT and ASK this includes HTML, XML, CSV, TSV and JSON formats. DESCRIBE and CONSTRUCT create an RDF::Graph, which can be serialized through HTTP Content Negotiation using available RDF writers. For best results, require Linked Data to enable a full set of RDF formats.

Examples

require 'rubygems'
require 'sparql'

Querying a repository with a SPARQL query

queryable = RDF::Repository.load("etc/doap.ttl")
sse = SPARQL.parse("SELECT * WHERE { ?s ?p ?o }")
queryable.query(sse) do |result|
  result.inspect
end

Executing a SPARQL query against a repository

queryable = RDF::Repository.load("etc/doap.ttl")
sse = SPARQL.parse("SELECT * WHERE { ?s ?p ?o }")
sse.execute(queryable) do |result|
  result.inspect
end

Rendering solutions as JSON, XML, CSV, TSV or HTML

queryable = RDF::Repository.load("etc/doap.ttl")
solutions = SPARQL.execute("SELECT * WHERE { ?s ?p ?o }", queryable)
solutions.to_json #to_xml #to_csv #to_tsv #to_html

Parsing a SPARQL query string to SSE

sse = SPARQL.parse("SELECT * WHERE { ?s ?p ?o }")
sse.to_sxp #=> (bgp (triple ?s ?p ?o))

Command line processing

sparql --default-graph etc/doap.ttl etc/from_default.rq
sparql -e "SELECT * FROM <etc/doap.ttl> WHERE { ?s ?p ?o }"

# Generate SPARQL Algebra Expression (SSE) format
sparql --to-sse etc/input.rq
sparql --to-sse -e "SELECT * WHERE { ?s ?p ?o }"

# Run query using SSE input
sparql --default-graph etc/doap.ttl --sse etc/input.sse
sparql --sse -e "(dataset (<etc/doap.ttl>) (bgp (triple ?s ?p ?o))))"

Adding SPARQL content negotiation to a Rails 3.x application

# config/application.rb
require 'rack/sparql'

class Application < Rails::Application
  config.middleware.use Rack::SPARQL::ContentNegotiation
end

Adding SPARQL content negotiation to a Rackup application

#!/usr/bin/env rackup
require 'rack/sparql'

repository = RDF::Repository.new do |graph|
  graph << [RDF::Node.new, RDF::DC.title, "Hello, world!"]
end
results = SPARQL.execute("SELECT * WHERE { ?s ?p ?o }", repository)

use Rack::SPARQL::ContentNegotiation
run lambda { |env| [200, {}, results] }

Adding SPARQL content negotiation to a classic Sinatra application

# Sinatra example
#
# Call as http://localhost:4567/sparql?query=uri,
# where `uri` is the URI of a SPARQL query, or
# a URI-escaped SPARQL query, for example:
#   http://localhost:4567/?query=SELECT%20?s%20?p%20?o%20WHERE%20%7B?s%20?p%20?o%7D
require 'sinatra'
require 'sinatra/sparql'
require 'uri'

get '/' do
  settings.sparql_options.replace(:standard_prefixes => true)
  repository = RDF::Repository.new do |graph|
    graph << [RDF::Node.new, RDF::DC.title, "Hello, world!"]
  end
  if params["query"]
    query = params["query"].to_s.match(/^http:/) ? RDF::Util::File.open_file(params["query"]) : ::URI.decode(params["query"].to_s)
    SPARQL.execute(query, repository)
  else
    settings.sparql_options.merge!(:prefixes => {
      :ssd => "http://www.w3.org/ns/sparql-service-description#",
      :void => "http://rdfs.org/ns/void#"
    })
    service_description(:repo => repository)
  end
end

Find more examples in {SPARQL::Grammar} and {SPARQL::Algebra}.

Documentation

Full documentation available on Rubydoc.info

Principle Classes

• {SPARQL}
  • {SPARQL::Algebra}
    • {SPARQL::Algebra::Expression}
    • {SPARQL::Algebra::Query}
    • {SPARQL::Algebra::Operator}
  • {SPARQL::Grammar}
    • {SPARQL::Grammar::Parser}
• {Sinatra::SPARQL}
• {Rack::SPARQL}
  • {Rack::SPARQL::ContentNegotiation}

Dependencies

• Ruby (>= 1.9.2)
• RDF.rb (>= 1.0.7)
• SPARQL::Client (>= 1.0.3)
• SXP (>= 0.1.0)
• Builder (>= 3.0.0)
• JSON (>= 1.5.1)
• Soft dependency on Linked Data (>= 1.0)
• Soft dependency on Nokogiri (>= 1.5.0) Falls back to REXML for XML parsing Builder for XML serializing. Nokogiri is much more efficient
• Soft dependency on Equivalent XML (>= 0.3.0) Equivalent XML performs more efficient comparisons of XML Literals when Nokogiri is included
• Soft dependency on Rack (>= 1.4.4)
• Soft dependency on Sinatra (>= 1.3.3)

Installation

The recommended installation method is via RubyGems. To install the latest official release of the SPARQL gem, do:

% [sudo] gem install sparql

Download

To get a local working copy of the development repository, do:

% git clone git://github.com/ruby-rdf/sparql.git

Mailing List

• http://lists.w3.org/Archives/Public/public-rdf-ruby/

Authors

• Gregg Kellogg - http://greggkellogg.net/
• Arto Bendiken - http://ar.to/
• Pius Uzamere - http://pius.me/

Contributing

This repository uses Git Flow to mange development and release activity. All submissions must be on a feature branch based on the develop branch to ease staging and integration.

• Do your best to adhere to the existing coding conventions and idioms.
• Don't use hard tabs, and don't leave trailing whitespace on any line.
• Do document every method you add using YARD annotations. Read the tutorial or just look at the existing code for examples.
• Don't touch the .gemspec, VERSION or AUTHORS files. If you need to change them, do so on your private branch only.
• Do feel free to add yourself to the CREDITS file and the corresponding list in the the README. Alphabetical order applies.
• Do note that in order for us to merge any non-trivial changes (as a rule of thumb, additions larger than about 15 lines of code), we need an explicit public domain dedication on record from you.

License

This is free and unencumbered public domain software. For more information, see http://unlicense.org/ or the accompanying {file:UNLICENSE} file.

A copy of the SPARQL EBNF and derived parser files are included in the repository, which are not covered under the UNLICENSE. These files are covered via the W3C Document License.

A copy of the SPARQL 1.0 tests and SPARQL 1.1 tests are also included in the repository, which are not covered under the UNLICENSE; see the references for test copyright information.