QLever

From OpenStreetMap Wiki
Jump to navigation Jump to search
QLever
Authors: ad-freiburg GitHub (Hannah Bast, Johannes Kalmbach, Patrick Brosi + many others)
Platforms: Linux, macOS, and others
Website: https://qlever.cs.uni-freiburg.de/osm-planet
Source code: ad-freiburg/qlever GitHub and ad-freiburg/osm2rdf GitHub

An efficient SPARQL engine for very large datasets, including the complete OpenStreetMap data. Provides context-sensitive autocompletion, efficient support for geometric "contains" and "intersects" queries, and an interactive display of a large number of geometric objects on a map.

QLever is an open-source general-purpose SPARQL engine with partial support for OGC GeoSPARQL 1.1. The public website provides access to SPARQL endpoints for a variety of large datasets, including RDF versions of the complete OpenStreetMap and OpenHistoricalMap datasets. Alternatively, you can set up a QLever instance locally yourself, as described below.

Notable features of QLever that are relevant for the OpenStreetMap data are:

  • QLever can handle very large datasets efficiently. The OpenStreetMap data, when converted to RDF, has around 40 billion triples, see https://github.com/ad-freiburg/osm2rdf.
  • SPARQL is a fully standardized query language. In particular, it allows easy federated search over mutiple datasets, for example, the OpenStreetMap data and Wikidata. Here is an example query: the power network of the EU .
  • QLever provides context-sensitive autocompletion for writing SPARQL queries. That way, one can write queries without being an expert in SPARQL and without being familiar with the schema of the data.
  • QLever provides efficient support for the GeoSPARQL predicates ogc:sfContains and ogc:sfIntersects. For example: all streets in in the Alps.
  • QLever can show large numbers of geometric objects on map interactively. For example, the query from the previous item returns around 4 million objects; to display them, click on the MapView button on the top right of the result list.

How to query OSM

  • Choose the OSM Planet or OHM Planet dataset
  • Choose an entry from the menu Examples at the bottom right or type your own query using the autocompletion
  • For query results with geometric information in the last column, a Map Viewbutton appears
  • Via the Download button, you can download the query results in various formats
  • Via the Sharebutton, you can copy&paste a variety of API calls corresponding to the current query

Data status

QLever's OpenStreetMap coverage is based on the latest weekly planet file that has been processed into an osm2rdf dataset. Therefore, the data can be up to two weeks behind the OSM database. Expand the Index Information panel of the OSM Planet query tool to see the timestamp. QLever's OpenHistoricalMap coverage is based on OHM's daily planet, so it can be up to one day old.

Prefixes

Prefix URL Description
osmnode: https://www.openstreetmap.org/node/ Node IDs
osmway: https://www.openstreetmap.org/way/ Way IDs
osmrel: https://www.openstreetmap.org/relation/ Relation IDs, plus relation metakeys such as osmrel:member
osmkey: https://www.openstreetmap.org/wiki/Key: Keys
osmmeta: https://www.openstreetmap.org/meta/ Element metakeys such as osmmeta:timestamp
osm2rdf: https://osm2rdf.cs.uni-freiburg.de/rdf# Metakeys added by osm2rdf such as osm2rdf:facts, osm2rdf:length, and osm2rdf:area
osm2rdfkey: https://osm2rdf.cs.uni-freiburg.de/rdf/key# Keys reinterpreted as RDF types by osm2rdf, such as osm2rdfkey:wikidata (as wd:)
osm2rdfmember: https://osm2rdf.cs.uni-freiburg.de/rdf/member# Relation member metakeys such as osm2rdfmember:role and osm2rdfmember:id

Some of these prefixes are shared with OpenHistoricalMap.

Examples

Self-hosting

QLever is open source and easy to use. To set up your own QLever instance, go to https://github.com/ad-freiburg/qlever-control and follow the instructions there. To setup a QLever instance for the OpenStreetMap data, do the following

  • Install the qlever script by following the instructions on https://github.com/ad-freiburg/qlever-control
  • Do qlever setup-config osm-planet to get a prefilled config file (called Qleverfile) for the OpenStreepMap data
  • Edit Qleverfile in case you want to download only the data for a particular country (e.g., for testing)
  • Do qlever get-data to download the data from https://osm2rdf.cs.uni-freiburg.de/
  • Do qlever index to build a QLever index for that data (indexing speed up to 5 billion triples per hour on modern hardware)
  • Do qlever start to start the server
  • Do qlever test-query to launch a test query and check whether everythings works
  • Do qlever ui to launch a version of the QLever UI like the one on https://qlever.cs.uni-freiburg.de/osm-planet
  • Do qlever autocompletion-warmup to speed up the autocompletion in the UI

External links

Retrieved from "https://wiki.openstreetmap.org/w/index.php?title=QLever&oldid=2765790"