SPARQL Query and Update library for Ruby

An implementation of SPARQL for RDF.rb.

Features

• 100% free and unencumbered public domain software.
• Complete SPARQL 1.1 Query parsing and execution
• 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 (via sparql-client).
• SPARQL 1.1 Protocol (via {SPARQL::Server}).
• SPARQL 1.1 Update
• 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
  • Helper method for setting up datasets as part of the SPARQL 1.1 Protocol.
• Implementation Report: {file:etc/earl.html EARL}
• Compatible with Ruby >= 2.6.
• Supports Unicode query strings both on all versions of Ruby.
• Provisional support for SPARQL-star.

Description

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

• {SPARQL::Grammar} implements a SPARQL 1.1 Query and SPARQL 1.1 Update parser generating SPARQL S-Expressions (SSE).
• {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::Server} implements the SPARQL 1.1 Protocol using {Sinatra::SPARQL}.

SPARQL 1.1 Query Extensions and Limitations

The {SPARQL} gem uses the SPARQL 1.1 Query {file:etc/sparql11.html 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
• Property Paths

The gem also includes the following SPARQL 1.1 Update operations:

• Graph Update
• Graph Management

Not supported:

• Federated Query,
• Entailment Regimes, and
• Graph Store HTTP Protocol but the closely related Linked Data Platform implemented in rdf-ldp supports these use cases.

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 1.2

The gem supports some of the extensions proposed by the SPARQL 1.2 Community Group. In particular, the following extensions are now implemented:

• SEP-0002: better support for Durations, Dates, and Times
  • This includes full support for xsd:date, xsd:time, xsd:duration, xsd:dayTimeDuration, and xsd:yearMonthDuration along with associated XPath/XQuery functions including a new ADJUST builtin. (Note: This feature is subject to change or elimination as the standards process progresses.)
• SEP-0003: Property paths with a min/max hop
  • This includes support for non-counting path forms such as rdf:rest{1,3} to match the union of paths rdf:rest, rdf:rest/rdf:rest, and rdf:rest/rdf:rest/rdf:rest. (Note: This feature is subject to change or elimination as the standards process progresses.)

SPARQL Extension Functions

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

# Register a function using the IRI <https://rubygems#crypt>
crypt_iri = RDF::URI("https://rubygems#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: <https://rubygems#>
PREFIX schema: <http://schema.org/>
SELECT ?crypted
{
  [ schema:email ?email]
  BIND(rsp:crypt(?email) AS ?crypted)
}

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

Variable Pre-binding

A call to execute a parsed query can include pre-bound variables, which cause queries to be executed with matching variables bound as defined. Variable pre-binding can be done using a Hash structure, or a Query Solution. See Query with Binding example and {SPARQL::Algebra::Query#execute}.

SPARQLStar (SPARQL-star)

The gem supports SPARQL-star where patterns may include sub-patterns recursively, for a kind of Reification.

For example, the following Turtle* file uses a statement as the subject of another statement:

@prefix : <http://bigdata.com/> .
@prefix foaf: <http://xmlns.com/foaf/0.1/> .
@prefix ex:  <http://example.org/> .

:bob foaf:name "Bob" .
<<:bob foaf:age 23>> ex:certainty 0.9 .

This can be queried using the following query:

PREFIX : <http://bigdata.com/>
PREFIX foaf: <http://xmlns.com/foaf/0.1/>
PREFIX ex:  <http://example.org/>

SELECT ?age ?c WHERE {
   ?bob foaf:name "Bob" .
   <<?bob foaf:age ?age>> ex:certainty ?c .
}

This treats <<:bob foaf:age 23>> as a subject resource, and the pattern <<?bob foaf:age ?age>> to match that resource and bind the associated variables.

Note: This feature is subject to change or elimination as the standards process progresses.

BIND

There is an alternate syntax using the BIND operator:

PREFIX : <http://bigdata.com>
PREFIX foaf: <http://xmlns.com/foaf/0.1/>
PREFIX dct:  <http://purl.org/dc/elements/1.1/>

SELECT ?a ?b ?c WHERE {
   ?bob foaf:name "Bob" .
   BIND( <<?bob foaf:age ?age>> AS ?a ) .
   ?t ?b ?c .
}

When binding, the triple can be either in Property Graph (:PG) or Separate Assertions (:SA) mode, as the query matches based on the pattern matching as a subject (or object) and does not need to be specifically asserted in the graph. When parsing in Property Graph mode, such triples will also be added to the enclosing graph. Thus, querying for <<?bob foaf:age ?age>> and ?bob foaf:age ?age may not represent the same results.

When binding an embedded triple to a variable, it is the matched triples which are bound, not the pattern. Thus, the example above with SELECT ?a ?b ?c would end up binding ?a to :bob foaf:name 23.

Construct

As well as a CONSTRUCT:

PREFIX : <http://bigdata.com>
PREFIX foaf: <http://xmlns.com/foaf/0.1/>
PREFIX dct:  <http://purl.org/dc/elements/1.1/>

CONSTRUCT {
  ?bob foaf:name "Bob" .
  <<?bob foaf:age ?age>> ?b ?c .
}
WHERE {
  ?bob foaf:name "Bob" .
  <<?bob foaf:age ?age>> ?b ?c .
}

Note that results can be serialized only when the format supports RDF-star.

SPARQL results

The SPARQL results formats are extended to serialize quoted triples as described for RDF4J:

{
  "head" : {
    "vars" : ["a", "b", "c"]
  },
  "results" : {
    "bindings": [
      { "a" : {
          "type" : "triple",
          "value" : {
            "s" : {"value" : "http://example.org/bob", "type": "uri"},
            "p" : {"value" : "http://xmlns.com/foaf/0.1/name", "type": "uri"},
            "o" : {
              "value" : "23",
              "type" : "literal",
              "datatype" : "http://www.w3.org/2001/XMLSchema#integer"
            }
          }
        },
        "b": {"value": "http://example.org/certainty", "type": "uri"},
        "c" : {
          "value" : "0.9",
          "type" : "literal",
          "datatype" : "http://www.w3.org/2001/XMLSchema#decimal"
        }
      }
    ]
  }
}

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. Content negotiation also transforms application/x-www-form-urlencoded to either application/sparql-query or application/sparql-update as appropriate for SPARQL 1.1 Protocol.

{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 (via {Sinatra::SPARQL::Helpers.service_description} and protocol-based dataset mangement via {Sinatra::SPARQL::Helpers.dataset} for default-graph-uri and named-graph-uri The using-graph-uri and using-named-graph-uri query parameters are managed through {SPARQL::Algebra::Operator::Modify#execute}.

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.)

Server

A simple Sinatra-based server is implemented in {SPARQL::Server.application} using {Rack::SPARQL} and {Sinatra::SPARQL} completes the implementation of SPARQL 1.1 Protocol and can be used to compose a server including other capabilities.

Remote datasets

A SPARQL query containing FROM or FROM NAMED (also UPDATE or UPDATE NAMED) will load the referenced IRI unless the repository already contains a graph 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")
query = SPARQL.parse("SELECT * WHERE { ?s ?p ?o }")
queryable.query(query) do |result|
  result.inspect
end

Executing a SPARQL query against a repository

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

Updating a repository

queryable = RDF::Repository.load("etc/doap.ttl")
update = SPARQL.parse(%(
  PREFIX doap: <http://usefulinc.com/ns/doap#>
  INSERT DATA { <https://rubygems> doap:implements <http://www.w3.org/TR/sparql11-update/>}
), update: true)
update.execute(queryable)

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

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

Parsing a SSE to SPARQL query or update string to SPARQL

# Note: if the SSE uses extension functions, they either must be XSD casting functions, or custom functions which are registered extensions. (See [SPARQL Extension Functions](#sparql-extension-functions))

query = SPARQL::Algebra.parse(%{(bgp (triple ?s ?p ?o))})
sparql = query.to_sparql #=> "SELECT * WHERE { ?s ?p ?o }"

Query with Binding

bindings = {page: RDF::URI("https://greggkellogg.net/")}
queryable = RDF::Repository.load("etc/doap.ttl")
query = SPARQL.parse(%(
  PREFIX foaf: <http://xmlns.com/foaf/0.1/>
  SELECT ?person
  WHERE {
    ?person foaf:homepage ?page .
  }
))
solutions = query.execute(queryable, bindings: bindings)
solutions.to_sxp #=> (((person <https://greggkellogg.net/foaf#me>)))

Command line processing

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

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

# Generate SPARQL Query from SSE
sparql parse --sse etc/input.sse --format sparql
sparql parse --sse --format sparql -e "(dataset (<http://usefulinc.com/ns/doap>) (bgp (triple ?s ?p ?o))))"

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

# Run a local SPARQL server using a dataset
sparql server etc/doap.ttl

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::Vocab::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::Vocab::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 (>= 2.6)
• RDF.rb (~> 3.2)
• SPARQL::Client (~> 3.1)
• SXP (~> 1.2)
• Builder (~> 3.2)
• JSON (~> 2.6)
• Soft dependency on Linked Data (>= 3.1)
• Soft dependency on Nokogiri (~> 1.12) Falls back to REXML for XML parsing Builder for XML serializing. Nokogiri is much more efficient
• Soft dependency on Equivalent XML (>= 0.6) Equivalent XML performs more efficient comparisons of XML Literals when Nokogiri is included
• Soft dependency on Rack (~> 2.2)
• Soft dependency on Sinatra (~> 2.1)

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

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

Authors

• Gregg Kellogg - https://greggkellogg.net/
• Arto Bendiken - https://ar.to/
• Pius Uzamere - https://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, which you will be asked to agree to on the first commit to a repo within the organization. Note that the agreement applies to all repos in the Ruby RDF organization.

License

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

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.