Unofficial extensions for jena - refactoring of https://github.com/SmartDataAnalytics/jena-sparql-api

Maven Dependencies

We recommend to import the jenax bom file in order to ensure consistent versions among the dependencies:

<dependency>
    <groupId>org.aksw.jenax</groupId>
    <artifactId>jenax-bom</artifactId>
    <version>${jenax.version}</version>
    <type>pom</type>
    <scope>import</scope>
</dependency>

Highlights

Some components that deserve particular recognition:

• FunctionBinder: Annotate Java functions and let the function binder do the work to enable their use in SPARQL.
• Reprogen (Resource Proxy Generator): Tired of writing code to brigde the Java object world with the RDF graph world? Let reprogen generate those bindings from annotated interfaces. Supports generation of mutable java.util.{Set, List, Map} views that read/write through to a Jena Model. Do you need an approach to generate IRIs for your classes in a controlled and deterministic way from only a subset of the RDF graph that backs your object graph? Then you may want to give Reprogen’s annotation-based skolemizer a try.
• SliceCache: Low-latency caching of slices of SPARQL result sets. Clients can read slices of data concurrently while they are being retrieved. A configurable amount of pages is kept in an LRU (least-recently-used) memory cache and after a configurable delay they are synced to disk.
• BinarySearcher: A hadoop-based implementation for performing binary search on seekable streams. Allows for looking up information by subject in (compressed) ntriples files. The DBpedia Databus is a data catalog system that forsaw this use case and already provides the appropriate metadata.

Qlever Integration

1. Install our jena fork. Our JenaX code relies on fixes and improvements of the jena-serviceenhancer module. These improvements need yet to be played back to the official Jena.

git clone https://github.com/Aklakan/jena.git jena-se
cd jena-se
git switch se-fixes-2023-11-29
mvn -Dmaven.test.skip clean install

1. Build the JenaX plugins bundle, which includes the Qlever assembler. Note that FUSEKI_EXTRA_JARS_FOLDER is the folder for extra jars of your Fuseki setup.

# Run these commands from <jenax-project-root> to build the plugins bundle:

cd jenax-bom
mvn -T1C -Dmaven.test.skip -Pext -pl :jenax-arq-plugins-bundle -am clean package
cd ..
cp ./jenax-arq-parent/jenax-arq-plugins-parent/jenax-arq-plugins-bundle/target/jenax-arq-plugins-bundle-5.5.0-1-SNAPSHOT.jar \
  FUSEKI_EXTRA_JARS_FOLDER

1. Create an assembler configuration such as <fuseki-root>/run/configuration/qlever_ds.ttl:

PREFIX fuseki:    <http://jena.apache.org/fuseki#>
PREFIX rdf:       <http://www.w3.org/1999/02/22-rdf-syntax-ns#>
PREFIX ja:        <http://jena.hpl.hp.com/2005/11/Assembler#>
PREFIX qlever:    <http://jena.apache.org/qlever#>

<#service> rdf:type fuseki:Service ;
    fuseki:name "qlever" ;
    fuseki:endpoint [
      fuseki:operation fuseki:query ;
    ] ;
    fuseki:dataset  <#baseDS>
   .

<#baseDS> rdf:type qlever:Dataset ;
  qlever:location "/run/databases/qlever/mydb/" ;
  qlever:indexName "myindex" ;
  qlever:accessToken "abcde" ;
  qlever:memoryMaxSize "4G" ;
  qlever:defaultQueryTimeout "600s" ;
  .

Docker-outside-of-Docker (DooD) Setup.

If Fuseki runs in a docker container then it can start qlever as a secondary container based on the assembler config. However, this requires additional configuration which may differ between environments. The following describes a typical setup on Ubuntu 24.04.

docker-compose.yml:

In this setup:

• Fuseki under the current user’s UID and GID (-> APP_UID, APP_GID)
• Mounts the docker socket into the container (/var/run/docker.sock)
• Adds the container’s user to the docker group (-> group_add of DOCKER_GID)
• Caveat: A firewall may prevent the Fuseki docker container from communicating with the ryuk container from the TestContainers framework.

name: semantic-stack

services:
  fuseki:
    image: aksw/fuseki-geoplus:5.5.0-1
    init: true
    user: "${APP_UID}:${APP_GID}"
    environment:
      - JAVA_OPTIONS=-Xmx8G -XX:ReplayDataFile=/run/log/fuseki_replay_pid%p.log -XX:ErrorFile=/run/log/fuseki_hs_err_pid%p.log -Dderby.stream.error.file=/run/log/fuseki_derby.log
      - FUSEKI_BASE=/run
    group_add:
      - "${DOCKER_GID}"
    volumes:
      - ./run:/run
      - /var/run/docker.sock:/var/run/docker.sock
    ports:
      - 3030:3030
      - 5005:5005
    restart: unless-stopped
    networks:
      - semantic-stack-net

networks:
  semantic-stack-net:

Invocation (feel free to use a .env file for the env variables):

APP_UID=`id -u` \
APP_GID=`id -g` \
DOCKER_GID=`getent group docker | cut -d: -f3` \
docker compose -f docker-compose.yml up