RDF For Haskell

rdf4h is a library for working with RDF in Haskell. At present it includes parsers and serializers for RDF in the N-Triples and Turtle formats, and parsing support for RDF/XML. It provides abilities such as querying for triples containing a particular subject, predicate, or object, or selecting triples that satisfy an arbitrary predicate function.

Installation

Once the Haskell platform has been installed, simply:

$ cabal update
$ cabal install rdf4h

Usage

The rdf4h library is split in to two parts.

• Data.RDF defines the RDF, RdfSerializer and RdfParser type classes. It also provides an API for RDF graph inspection.
• Text.RDF.RDF4H.* provides the parsers and serializers for supported RDF formats.

Example

{-# LANGUAGE OverloadedStrings #-}

import Data.RDF
import Data.RDF.TriplesGraph
import Text.RDF.RDF4H.NTriplesParser

rdfGraph1 :: IO TriplesGraph
rdfGraph1 = fmap fromEither (parseFile NTriplesParser "test1.nt")

rdfGraph2 :: IO TriplesGraph
rdfGraph2 = fmap fromEither (parseFile NTriplesParser "test2.nt")

example :: IO ()
example = do
  g1 <- rdfGraph1
  g2 <- rdfGraph2
  let node1 = lnode $ PlainL "foo"
  putStrLn $ "Subjects of g1: " ++ show (map subjectOf (triplesOf g1))
  putStrLn $ "RDF contains literal 'foo': " ++ show (rdfContainsNode g1 node1)
  putStrLn $ "Isomorphism test: " ++ show (isIsomorphic g1 g2)
  putStrLn $ "Unsorted triples: " ++ show (triplesOf g2)
  putStrLn $ "Sorted triples: "   ++ show ((sort . triplesOf) g2)
  putStrLn $ "Query: " ++ show (query g1 Nothing Nothing (Just node1))

Development

Contributions are welcome. A rewrite of the RDF type class API will happen in the future. Additions to Data.RDF.Types and Data.RDF.Query, fixes to the three parsers, and an RDF/XML serialiser would be great. Writing tests is highly encouraged.

Issues

Please use the GitHub issue tracker to report any bugs you might find. New contributors are most welcome! See the TODO.org file for some ideas on how to contribute.

Related Haskell Packages

• hsparql is a DSL for programmatic creation and execution of SPARQL queries. It makes use of the RDF type class in rdf4h, allowing the two packages to be combined easily.
• swish is a toolkit for RDF inference and for implementing RDF file processors. It explores Haskell as "a scripting language for the semantic web".