white-gecko / adhs

Ad-hoc light weight SPARQL endpoint from a file, using Python Flask and RDFlib

adhs

Ad-hoc light weight SPARQL endpoint from a file, using Python Flask and RDFLib

Details

Sometimes one needs to set up a quick SPARQL endpoint for a local Turtle file without installing a triplestore. This is a quick demo how to use the Python 3 microframework Flask and RDFLib to provide an Ad-Hoc SPARQL endpoint based on a Turtle or RDF/XML file.

Installation

adhs requires python > 3. You can install dependencies with pip:

pip install -r requirements.txt

Usage

Example:

./adhs.py file.ttl -i turtle -p 5000

The -i parameter is optional but should be used to specify the format of the file. If it's missing, rdflib.util.guess_format() will be used.

The parameter --host is optional too, and defines the interfaces where the hosts is listening (127.0.0.1 for local only, 0.0.0.0 for all interfaces).

The -p parameter is optional as well. If not provided, flask will be accessible on default port 5000. Navigate to

http://localhost:5000/sparql

to get a very basic form to enter and submit your queries (the form is just some icing on the cake).

Additionally, the SPARQL endpoint accepts GET and POST requests.

Example of a GET request via URL:

http://localhost:5000/sparql?query=select distinct ?s where { ?s a ?c }&format=<CONTENT-TYPE>

The format has to be specified via the accept type (see below) but in future there might be more fine-grained options.

Note: Instead of format, the parameter output can be used as well.

Example with cURL:

curl -d "query=select distinct ?c where {?s a ?c}" \
     -H "Accept: text/html" \
     localhost:5000/sparql

The content type has to be application/x-www-form-urlencoded, whereas the accept type can be one of the following:

• text/html
• application/sparql-results+json
• application/sparql-results+xml

Additionally, the accept type can also be set with the format (or alternatively) output parameter.

If no accept type is specified, the default type is text/html unless it's overridden with format or output. When an accept type is set via content negotiation and as well with the format or output parameter, the parameter takes precedence over the content negotiation.

Docker Image

adhs is also available as an automatic image build at hub.docker.com, so you can serve a local file with the following docker command:

docker run -i -t --rm -p 80:80 -v $PWD:/data -e ADHS_FILE=/data/ontology.ttl eccenca/adhs:latest

adhs docker understands the following environment variables:

• ADHS_FILE corresponds to the file parameter of adhs
• ADHS_INPUT corresponds to the optional input parameter -i.

In dockerized adhs, the port is set to 80 and the host to 0.0.0.0 (all interfaces). Volume is set to /data so you can mount your data directory into it. In addition to that /opt/adhs/templates is also a volume if you want to overwrite the templates.

Use case

One use case behind the adhs was to provide a quick possibility to set up different ontologies to test them with the Visual SPARQL Builder (VSB) without having to load them into a triplestore like Virtuoso. Additionally, since the VSB needs SPARQL 1.1, it is a convenient alternative on systems don't have high enough version of Virtuoso installed.

Fun facts

ADHS is actually the German abbreviation for ADHD.

Future Work

moved to TODO.md