MongoDB and Knowledge Graphs

How to model a knowledge graph in MongoDB, incl. ontologies and an example based on public data from OpenStreetMap

Prerequisites

Latest stable Python 3 with the following (TODO: pyld, requests, rdflib, rdflib-jsonld, esy, esy-osm-pbf) modules installed
Java JDK
pbf2json download from https://github.com/pelias/pbf2json
owl2jsonld download from https://github.com/stain/owl2jsonld
Latest stable MongoDB installed locally or accessible. Connection is currently configured to use local instance without authentication
OSM data in PBF format at choice.

Import raw data of keys and values of OSM data: python3 import_osm_metadata.py
Derive ontology python3 derive_ontology.py

After running derive_ontology.py the files osmpower.jsonld and osmpower.ttl are created.

Import OSM data (can be a whole country, or just some parts): https://www.geofabrik.de/data/download.html e.g. bayern-latest.osm.pbf. Change INPUT_OSM_FILE in import_osm_data.py accordingly.
To import raw data of .osm.pbf file to MongoDB import_osm_data.py the file pbf2json.darwin-x64 (for your OS of choice) is needed. Change command in import_osm_data.py accordingly. Then run with python3 import_osm_data.py. When running, the script seems to hang, but it does finish (needs to be documented or changed, as the Java process is called from the Python script. Bit hacky, but works more or less fine). You can stop with Control-C, as soon as no new objects are inserted into raw_objects_germany (should be just raw_objects <- final polishing).
Next step is to run python3 derive_instances.py to get the instance data as TTL file and in the collection "instance". The file owl2jsonld is needed. Change OWL_TO_JSON_JAR_ABSOLUTE_PATH in derive_instances.py accordingly. Please double-check if the collection name in derive_instances.py is correct, must be "raw_objects_germany" (those imported earlier).

When running script reports progress creating assets:

Processed 296000 Assets
Processed 297000 Assets
Create partOf and hasPart relationships

After running derive_instances.py the file osmpower_bavaria.ttl is created (NOTE: file name is hardcoded in script).