RDF::Turtle reader/writer

Turtle reader/writer for RDF.rb .

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Description

This is a Ruby implementation of a Turtle parser for RDF.rb.

Features

RDF::Turtle parses Turtle and N-Triples into statements or triples. It also serializes to Turtle.

Install with gem install rdf-turtle

  • 100% free and unencumbered public domain software.
  • Implements a complete parser for Turtle.
  • Compatible with Ruby >= 2.2.2.
  • Optional streaming writer, to serialize large graphs
  • Provisional support for Turtle*.

Usage

Instantiate a reader from a local file:

graph = RDF::Graph.load("etc/doap.ttl", format:  :ttl)

Define @base and @prefix definitions, and use for serialization using :base_uri an :prefixes options.

Canonicalize and validate using :canonicalize and :validate options.

Write a graph to a file:

RDF::Turtle::Writer.open("etc/test.ttl") do |writer|
   writer << graph
end

Turtle* (RDFStar)

Both reader and writer include provisional support for Turtle*.

Internally, an RDF::Statement is treated as another resource, along with RDF::URI and RDF::Node, which allows an RDF::Statement to have a #subject or #object which is also an RDF::Statement.

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

Serializing a Graph containing embedded statements

require 'rdf/turtle'
statement = RDF::Statement(RDF::URI('bob'), RDF::Vocab::FOAF.age, RDF::Literal(23))
graph = RDF::Graph.new << [statement, RDF::URI("ex:certainty"), RDF::Literal(0.9)]
graph.dump(:ttl, validate: false, standard_prefixes: true)
# => '<<<bob> foaf:age 23>> <ex:certainty> 9.0e-1 .'

Reading a Graph containing embedded statements

By default, the Turtle reader will reject a document containing a subject resource.

ttl = %(
  @prefix foaf: <http://xmlns.com/foaf/0.1/> .
  @prefix ex: <http://example.com/> .
  <<<bob> foaf:age 23>> ex:certainty 9.0e-1 .
)
graph = RDF::Graph.new do |graph|
  RDF::Turtle::Reader.new(ttl) {|reader| graph << reader}
end
# => RDF::ReaderError

Readers support a rdfstar option with either :PG (Property Graph) or :SA (Separate Assertions) modes. In :PG mode, statements that are used in the subject or object positions are also implicitly added to the graph:

graph = RDF::Graph.new do |graph|
  RDF::Turtle::Reader.new(ttl, rdfstar: :PG) {|reader| graph << reader}
end
graph.count #=> 2

When using the :SA mode, only one statement is asserted, although the reified statement is contained within the graph.

graph = RDF::Graph.new do |graph|
  RDF::Turtle::Reader.new(ttl, rdfstar: :SA) {|reader| graph << reader}
end
graph.count #=> 1

Documentation

Full documentation available on Rubydoc.info

Principle Classes

Variations from the spec

In some cases, the specification is unclear on certain issues:

  • The LC version of the Turtle specification separates rules for @base and @prefix with closing '.' from the SPARQL-like BASE and PREFIX without closing '.'. This version implements a more flexible syntax where the @ and closing . are optional and base/prefix are matched case independently.
  • Additionally, both a and A match rdf:type.

Freebase-specific Reader

There is a special reader useful for processing Freebase Dumps. To invoke this, add the freebase: true option to the RDF::Turtle::Reader.new, or use RDF::Turtle::FreebaseReader directly. As with RDF::Turtle::Reader, prefix definitions may be passed in using the :prefixes option to RDF::Turtle::FreebaseReader} using the standard mechanism defined for RDF::Reader.

The Freebase Dumps have a very normalized form, similar to N-Triples but with prefixes. They also have a large amount of garbage. This Reader is optimized for this format and will perform faster error recovery.

An example of reading Freebase dumps:

require "rdf/turtle"
fb = "../freebase/freebase-rdf-2013-03-03-00-00.ttl"
fb_prefixes = {
  ns:  "http://rdf.freebase.com/ns/",
  key:  "http://rdf.freebase.com/key/",
  owl:  "http://www.w3.org/2002/07/owl#>",
  rdfs:  "http://www.w3.org/2000/01/rdf-schema#",
  rdf:  "http://www.w3.org/1999/02/22-rdf-syntax-ns#",
  xsd:  "http://www.w3.org/2001/XMLSchema#"
}
RDF::Turtle::Reader.open(fb,
  freebase:  true,
  prefixes:  fb_prefixes) do |r|

  r.each_statement {|stmt| puts stmt.to_ntriples}
end

Implementation Notes

This version uses a hand-written parser using the Lexer from the EBNF gem instead of a general EBNF LL(1) parser for faster performance.

Dependencies

Installation

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

% [sudo] gem install rdf-turtle

Mailing List

Author

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 https://unlicense.org/ or the accompanying UNLICENSE file.

A copy of the Turtle 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.