RMLMapper

The RMLMapper execute RML rules to generate Linked Data. It is a Java library, which is available via the command line. The RMLMapper loads all data in memory, so be aware when working with big datasets.

Features

Supported

local data sources:
CSV files
JSON files (JSONPath)
XML files (XPath)
remote data sources:
relational databases (MySQL, PostgreSQL, and SQLServer)
SPARQL endpoints
files via HTTP urls (via GET)
CSV files
JSON files (JSONPath)
XML files (XPath)
functions (most cases)
configuration file
metadata generation
output formats: turtle, trig, trix, jsonld, nquads
join conditions

Future

functions (all cases)
conditions (all cases)
data sources:
- NoSQL databases
- web APIs
- TPF servers

Build

The RMLMapper is build using Maven: mvn install. A standalone jar can be found in /target.

Usage

CLI

The following options are most common.

-m, --mapping <arg>: path to mapping document
-o, --output <arg>: path to output file
-s,--serialization <arg>: serialization format (nquads (default), trig, trix, jsonld, hdt)

All options can be found when executing java -jar rmlmapper.jar --help, that output is found below.

usage: java -jar mapper.jar <options>
options:
 -c,--configfile <arg>            path to configuration file
 -d,--duplicates                  remove duplicates in the output
 -e,--metadatafile <arg>          path to metadata-test-cases file
 -f,--functionfile <arg>          path to functions.ttl file (dynamic functions are found relative to functions.ttl)
 -h,--help                        show help info
 -l,--metadataDetailLevel <arg>   generate metadata-test-cases on given detail level (dataset - triple - term)
 -m,--mappingfile <arg>           path to mapping document
 -o,--outputfile <arg>            path to output file (default: stdout)
 -s,--serialization <arg>         serialization format (nquads (default), trig, trix, jsonld, hdt)
 -t,--triplesmaps <arg>           IRIs of the triplesmaps that should be executed in order, split by ',' (default is all triplesmaps)
 -v,--verbose                     show more details in debugging output

Library

An example of how you can use the RMLMapper as an external library can be found below.

import org.eclipse.rdf4j.model.Model;
import org.eclipse.rdf4j.rio.RDFFormat;
import org.eclipse.rdf4j.rio.Rio;

import be.ugent.rml.DataFetcher;
import be.ugent.rml.Executor;
import be.ugent.rml.records.RecordsFactory;
import be.ugent.rml.store.RDF4JStore;
import be.ugent.rml.store.QuadStore;

import java.io.FileInputStream;
import java.io.InputStream;


class Main {

    public static void main(String[] args) {

        String cwd = "/home/rml"; //path to default directory for local files
        String mappingFile = "/home/rml/mapping.rml.ttl"; //path to the mapping file that needs to be executed
        
        try {
            InputStream mappingStream = new FileInputStream(mappingFile);
            Model model = Rio.parse(mappingStream, "", RDFFormat.TURTLE);
            RDF4JStore rmlStore = new RDF4JStore(model);

            Executor executor = new Executor(rmlStore, new RecordsFactory(new DataFetcher(cwd, rmlStore)));
            QuadStore result = executor.execute(null);
        } catch (Exception e) {
            System.out.println(e.getMessage());
        }
    } 
}

Including functions

There are two ways to include (new) functions within the RML Mapper

dynamic loading: you add links to java files or jar files, and those files are loaded dynamically at runtime
preloading: you register functionality via code, and you need to rebuild the mapper to use that functionality

Registration of functions is done using a Turtle file, which you can find in src/main/resources/functions.ttl

The snippet below for example links an fno:function to a library, provided by a jar-file (GrelFunctions.jar).

grel:toUpperCase a fno:Function ;
  fno:name "to Uppercase" ;
  rdfs:label "to Uppercase" ;
  dcterms:description "Returns the input with all letters in upper case." ;
  fno:expects ( grel:valueParam ) ;
  fno:returns ( grel:stringOut ) ;
  lib:providedBy [
    lib:localLibrary "GrelFunctions.jar";
    lib:class "GrelFunctions";
    lib:method "toUppercase"
  ].

Dynamic loading

Just put the java or jar-file in the resources folder, at the root folder of the jar-location, or the parent folder of the jar-location, it will be found dynamically.

Note: the java or jar-files are found relative to the loaded functions.ttl. You can change the functions.ttl path using a commandline-option (-f).

Preloading

This overrides the dynamic loading. See the snippet below for an example of how to do it.

package be.ugent.rml;

import be.ugent.rml.functions.FunctionLoader;
import be.ugent.rml.functions.lib.GrelProcessor;
import be.ugent.rml.records.RecordsFactory;
import be.ugent.rml.store.QuadStore;
import com.google.common.io.Resources;

import java.io.File;
import java.net.URL;
import java.util.HashMap;
import java.util.Map;


class Main {

    public static void main(String[] args) {
        String mapPath = "path/to/mapping/file";
        String functionPath = "path/to/functions.ttl/file";

        URL url = Resources.getResource(functionPath);
        
        Map<String, Class> libraryMap = new HashMap<>();
        libraryMap.put("GrelFunctions.jar", GrelProcessor.class);
        try {
            File functionsFile = new File(url.toURI());
            FunctionLoader functionLoader = new FunctionLoader(functionsFile, null, libraryMap);
            ClassLoader classLoader = Main.class.getClassLoader();
            // execute mapping file
            File mappingFile = new File(classLoader.getResource(mapPath).getFile());
            QuadStore rmlStore = Utils.readTurtle(mappingFile);
            
            Executor executor = new Executor(rmlStore, new RecordsFactory(new DataFetcher(mappingFile.getParent(), rmlStore)),
                functionLoader);
            QuadStore result = executor.execute(null);
        } catch (Exception e) {
            System.out.println(e.getMessage());
        }
    }
}

Testing

RDBs

Make sure you have Docker running.

Problems

A problem with Docker (can't start the container) causes the SQLServer tests to fail locally. These tests will always succeed locally.
A problem with Docker (can't start the container) causes the PostgreSQL tests to fail locally on Windows 7 machines.

Dependencies

Dependency	License
com.spotify docker client	Apache License 2.0
com.h2database h2	Eclipse Public License 1.0 & Mozilla Public License 2.0
com.googlecode.zohhak	GNU Lesser General Public License v3.0
com.microsoft.sqlserver mssql-jdbc	MIT
ch.vorbuger.mariaDB4j	Apache License 2.0
mysql-connector-java	GNU General Public License v2.0
com.google.guava	Apache License 2.0
javax.xml.parsers jaxp-api	Apache License 2.0
com.jayway.jsonpath	Apache License 2.0
junit	Eclipse Public License 1.0
org.eclipse.rdf4j rdf4j-runtime	Eclipse Public License 1.0
commons-cli	Apache License 2.0
com.opencsv opencsv	Apache License 2.0
commons-lang	Apache License 2.0
ch.qos.logback	Eclipse Public License 1.0 & GNU Lesser General Public License 2.1
org.rdfhdt.hdt-jena	GNU Lesser General Public License v3.0

Remarks

XML file parsing performance

The RMLMapper's XML parsing implementation (javax.xml.parsers) has been chosen to support full XPath. This implementation causes a large memory consumption (up to ten times larger than the original XML file size). However, the RMLMapper can be easily adapted to use a different XML parsing implementation that might be better suited for a specific use case.

UML Diagrams

How to generate with IntelliJ IDEA

(Requires Ultimate edition)

Right click on package: "be.ugent.rml"
Diagrams > Show Diagram > Java Class Diagrams
Choose what properties of the classes you want to show in the upper left corner
Export to file > .png | Save diagram > .uml

ecow/rmlmapper-java