Semagrow is a federated SPARQL query processor that allows combining, cross-indexing and, in general, making the best out of all public data, regardless of their size, update rate, and schema.
Semagrow offers a single SPARQL endpoint that serves data from remote data sources and that hides from client applications heterogeneity in both form (federating non-SPARQL endpoints) and meaning (transparently mapping queries and query results between vocabularies).
The main difference between Semagrow and most existing distributed querying solutions is that Semagrow targets the federation of heterogeneous and independently provided data sources.
In other words, Semagrow aims to offer the most efficient distributed querying solution that can be achieved without controlling the way data is distributed between sources and, in general, without having the responsibility to centrally manage the data sources of the federation.
Building Semagrow from sources requires to have a system with JDK8 and Maven 3.1 or higher.
Optionally, you may need a PostgreSQL as a requirement for the query transformation
functionality.
To build Semagrow you should type:
$ mvn clean installin the top-level project directory. This will result in jar file
in the target directory of the respective module and in a war file in the target directory of
the webgui module that can be deployed to the Servlet server of your choice.
Moreover, Semagrow can be build pre-bundled with the Apache Tomcat servlet server. To achieve that you could issue
$ mvn clean package -P tomcat-bundlefrom the top-level directory of the project. This will result in a
compressed file in the target directory of the assembly module
containing a fully equipped Apache Tomcat with Semagrow pre-installed.
However, please note that external dependencies such as the
PostgresSQL database needs to be installed and run separately.
You can also test your build deployed in a docker image (Docker 18.09 or newer required for building). To do so run at the project root directory:
$ DOCKER_BUILDKIT=1 docker build -t semagrow .The produced image will be tagged as semagrow:latest and will contain Tomcat with Semagrow deployed.
By default, Semagrow look for its configuration files in /etc/default/semagrow
and expects to find at least a repository.ttl and a metadata.ttl file in
order to establish a federation of endpoints. The repository.ttl describes
the configuration of the Semagrow endpoint, while the metadata.ttl describes
the endpoints to be federated. The repository.ttl configuration file
also defines the location of the metadata.ttl that can be changed to the desired
path.
Samples of these configuration files can be found as
resources of the http module
In order to run the bundle of Apache Tomcat with SemaGrow you should
- uncompress the generated zip,
- copy the files from the
resourcesfolder to/etc/default/semagrowand - run the
startup.shscript located in thebinfolder.
SemaGrow can be accessed at http://localhost:8080/SemaGrow/.
Semagrow has an official docker repository and official docker images are available in Docker Hub.
To run semagrow using the latest official docker image you should execute
$ docker run -d semagrow/semagrowHoweover, you can also build your own docker image using the steps described in Section [Building](#### Building a Docker image from sources)
The produced image will be tagged as semagrow and will contain Tomcat with Semagrow deployed.
To run the newly produced image you should execute
$ docker run -d semagrowor if you want to test Semagrow with your configuration files (repository.ttl and metadata.ttl) issue
$ docker run -d -v /path/to/configuration:/etc/default/semagrow semagrowIn either case you can access Semagrow at http://<CONTAINER_IP>:8080/SemaGrow/
where <CONTAINER_IP> is the address assigned to the semagrow container and can
be retrieved using docker inspect
- SemaGrow uses UNION instead of VALUES to implement the BindJoin operator. This fails in 4store 1.1.5 and previous versions in the presence of FILTER clauses due to an unsafe optimization by 4store.
- When deploying in Glassfish 4 by coping the SemaGrow.war file in the autodeploy directory, Semagrow is accessible at
http://DOMAIN/SemaGrow/index.jspinstead ofhttp://DOMAIN/SemaGrow/
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