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Turtle reader/writer for Ruby

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README.markdown

RDF::Turtle reader/writer

Turtle reader/writer for RDF.rb .

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 1.8.7+, Ruby 1.9.x, and JRuby 1.4/1.5.

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

Documentation

Full documentation available on Rubydoc.info

Principle Classes

  • {RDF::Turtle::Format}
    • {RDF::Turtle::TTL} Asserts :ttl format, text/turtle mime-type and .ttl file extension.
  • {RDF::Turtle::Reader}
  • {RDF::Turtle::Writer}

Variations from the spec

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

  • In section 2.1, the spec indicates that "Literals , prefixed names and IRIs may also contain escapes to encode surrounding syntax ...", however the description in 5.2 indicates that only IRI_REF and the various STRING_LITERAL terms are subject to unescaping. This means that an IRI which might otherwise be representable using a PNAME cannot if the IRI contains any characters that might need escaping. This implementation currently abides by this restriction. Presumably, this would affect both PNAME_NS and PNAME_LN terminals. (This is being tracked as issues 67).
  • The EBNF definition of IRI_REF seems malformed, and has no provision for ^, as discussed elsewhere in the spec. We presume that [#0000- ] is intended to be [#0000-#0020].
  • The list example in section 6 uses a list on it's own, without a predicate or object, which is not allowed by the grammar (neither is a blankNodeProperyList). Either the EBNF should be updated to allow for these forms, or the examples should be changed such that ( ... ) and [ ... ] are used only in the context of being a subject or object. This implementation will generate triples, however an error will be generated if the parser is run in validation mode.
  • For the time being, plain literals are generated without an xsd:string datatype, but literals with an xsd:string datatype are saved as non-datatyped triples in the graph. This will be updated in the future when the rest of the library suite is brought up to date.

Implementation Notes

The reader uses a generic LL1 parser {RDF::LL1::Parser} and lexer {RDF::LL1::Lexer}. The parser takes branch and follow tables generated from the original Turtle EBNF Grammar described in the specification. Branch and Follow tables are specified in {RDF::Turtle::Meta}, which is in turn generated using etc/gramLL1.

The branch rules indicate productions to be taken based on a current production. Terminals are denoted through a set of regular expressions used to match each type of terminal, described in {RDF::Turtle::Terminals}.

etc/turtle.bnf is used to to generate a Notation3 representation of the grammar, a transformed LL1 representation and ultimately {RDF::Turtle::Meta}.

Using SWAP utilities, this is done as follows:

python http://www.w3.org/2000/10/swap/grammar/ebnf2turtle.py \
  etc/turtle.bnf \
  ttl language \
  'http://www.w3.org/ns/formats/Turtle#' > |
sed -e 's/^  ".*"$/  g:seq (&)/'  > etc/turtle.n3

python http://www.w3.org/2000/10/swap/cwm.py etc/turtle.n3 \
  http://www.w3.org/2000/10/swap/grammar/ebnf2bnf.n3 \
  http://www.w3.org/2000/10/swap/grammar/first_follow.n3 \
  --think --data > etc/turtle-bnf.n3

script/gramLL1 \
  --grammar etc/turtle-ll1.n3 \
  --lang 'http://www.w3.org/ns/formats/Turtle#language' \
  --output lib/rdf/turtle/meta.rb

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

  • 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.

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