pyRML

pyRML is a Python based engine for processing RML files. The RDF Mapping Language (RML) is a mapping language defined to express customized mapping rules from heterogeneous data structures and serializations to the RDF data model. RML is defined as a superset of the W3C-standardized mapping language R2RML, aiming to extend its applicability and broaden its scope, adding support for data in other structured formats.

Installation

pyRML requires Python 3. Once the source code has been downloaded it is possible to install the Python package by means of pip. For example:

pip install .

Alternatively, it is possible to install the pyRML package directly from GitHub in the following way:

pip install git+https://github.com/anuzzolese/pyrml

Usage

It is possible to use pyRML either by means of its API or the command line tool that is provided along with the source package.

API

The RMLConverter is the key class of pyRML. It accepts the path to an RML file as input and returns an RDF graph as output. The output graph is an instance of the class Graph provided by RDFLib.

from pyrml import RMLConverter
import os

# Create an instance of the class RMLConverter.
rml_converter = RMLConverter()

'''
Invoke the method convert on the instance of class RMLConverter by:
 - using the file examples/artist/artist-map.ttl (see the examples in this repo);
 - obtaining an RDF graph as output.
'''
rml_file_path = os.path.join('examples', 'artists', 'artist-map.ttl')
rdf_graph = rml_converter.convert(rml_file_path)

# Print the triples contained into the RDF graph.
for s,p,o in rdf_graph:
    print(s, p, o)

Command line tool

The command line tool is implemented by the script converter.py. Such a script can be used in the following way:

python converter.py [-o RDF out file] [-f RDF out file] [-m] input

where:

• the positional argument input is the input RML mapping file for enabling the RDF conversion;
• the optional argument -o filename is the file to store the resulting RDF graph. If no choice is provided then standard output is assumed as default.
• the optional argument -f rdf-syntax can be used to specify the syntax to serialize the RDF graph. Possible values are n3, nquads, nt, pretty-xml, trig, trix, turtle, and xml. If no choice is provided then NTRIPLES is assumed as default.
• the optional flag -m enables the conversion based on multiprocessing for speeding up the transformation process.

The following is an example about how to use the command line tool for processing the RML file available in examples/artists/artist-map.ttl, thus converting the CSV files examples/artists/Artist.csv and examples/artists/Place.csv into an RDF graph serialized as TURTLE and stored into the file named artists_places.ttl.

python converter.py -o artists_places.ttl -f turtle examples/artists/artist-map.ttl