Linked Data Content Negotiation for Rack Applications

This is Rack middleware that provides Linked Data content negotiation for Rack applications. You can use Rack::RDF with any Ruby web framework based on Rack, including with Ruby on Rails 3.0 and with Sinatra.

This version is based on [rack-linkeddata][] without the hard dependency on the [linkeddata][] gem, to allow applications to better manage their dependencies

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  • Implements HTTP content negotiation for RDF content types.
  • Supports all RDF.rb compatible serialization formats.
  • Compatible with any Rack application and any Rack-based framework.


Adding RDF content negotiation to a Rails 3.x application

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

class Application < Rails::Application
  config.middleware.use Rack::RDF::ContentNegotiation

Adding RDF content negotiation to a Sinatra application

#!/usr/bin/env ruby -rubygems
require 'sinatra'
require 'rack/linkeddata'

use Rack::LinkedData::ContentNegotiation

get '/hello' do do |graph|
    graph << [, RDF::DC.title, "Hello, world!"]

Adding RDF content negotiation to a Rackup application

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

rdf = do |graph|
  graph << [, RDF::DC.title, "Hello, world!"]

use Rack::RDF::ContentNegotiation
run lambda { |env| [200, {}, rdf] }

Defining a default RDF content type

use Rack::RDF::ContentNegotiation, default: "text/turtle"

Options are also passed to the writer, which can allow options to be shared among the application and different components.

shared_options = {:default => "text/turtle", :standard_prefixes => true, }
use Rack::RDF::ContentNegotiation, shared_options
run MyApplication, shared_options

Testing RDF content negotiation using rackup and curl

$ rackup doc/examples/

$ curl -iH "Accept: text/plain" http://localhost:9292/hello
$ curl -iH "Accept: text/turtle" http://localhost:9292/hello
$ curl -iH "Accept: */*" http://localhost:9292/hello


Rack::RDF implements content negotiation for any Rack response object that implements the RDF::Enumerable mixin. You would typically return an instance of RDF::Graph or RDF::Repository from your Rack application, and let the Rack::RDF::ContentNegotiation middleware take care of serializing your response into whatever RDF format the HTTP client requested and understands.

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.)



  • Rack ('>= 2.2', '< 4')
  • RDF (~> 3.3)


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

% [sudo] gem install rack-rdf


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

% git clone git://

Alternatively, download the latest development version as a tarball as follows:

% wget


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.




This is free and unencumbered public domain software. For more information, see or the accompanying UNLICENSE file.