# Ontop with Dremio

In this tutorial we present step-by-step the way of connecting Dremio to Ontop. We show how to integrate uni1 data saved in the PostgreSQL database and uni2 data saved in plain JSON files into one Dremio data space.

Before you proceed, we recommend you to see the following tutorials provided by Dremio:

  1. Getting oriented with Dremio (opens new window)
  2. Working with your first dataset (opens new window)

As a first step, by following the instructions in Working with your first dataset (opens new window), we create a space named integrated_university_data as shown below.

Add new data space:

Save the new data space:

It will be our data space in which we integrate data from various sources.

The uni1 data is contained in a PostgreSQL database named university-session1. Either you can download the SQL script that generates the database from here and load it to your local PostgreSQL server, or you can run the docker container that we provide by executing the following script:

docker ps -q --filter ancestor=$IMAGENAME | xargs docker stop
docker build -t $IMAGENAME .
docker run -p 5435:5432 $IMAGENAME

The database university-session1 becomes accesable with the following JDBC URL:


Now we are ready to add our database as a new datasource into Dremio:

Select PostgreSQL:

Enter the required JDBC information:

Now we see the tables in university-session1:

We add the table course-registration as dataset into integrated_university_data. We rename it to uni1-registration.

Save the other datasets in similar manner.

Now we add the uni2 data as a JSON data source:

The uni2 JSON data can be seen as follows:

JSON files usually contain nested data. However, Ontop can not directly query nested data. For this reason, in order to make our JSON data queryable by Ontop, first we need to extract relevant group of elements, and save these groups as datasets.

With the following SQL query we create an uni2-registration dataset and save it into integrated data space integrated_university_data:

SELECT T.cid, T.enrollers.pid AS pid 
   SELECT cid, flatten(enrollers) AS enrollers 
   FROM uni2
) T

The following SQL expression flattens the array of enrollers:

flatten(enrollers) AS enrollers

Save As the data set with the name uni2-registration.

Create a dataset named uni2-course in a similar manner:

SELECT course, cid FROM uni2

Create a uni2-person dataset with a bit more involved SQL that unions both students and lecturers:

    SELECT uni2.lecturer."pid" AS pid, uni2.lecturer."fname" AS fname, uni2.lecturer."lname" AS lname 
    FROM uni2
    SELECT T.enrollers."pid" AS pid,T.enrollers."fname" AS fname, T.enrollers."lname" AS lnmae 
        SELECT flatten(enrollers) AS enrollers
        FROM uni2
    ) T
) F

Create uni2-teaching dataset with the following SQL:

SELECT cid, uni2.lecturer.pid AS pid
FROM uni2

Now we can list all the datasets we saved in the integrated_university_data space:

Finally we are ready to connect Dremio to Ontop. Dremio can be connected to Ontop through its JDBC interface. By following the instructions provided in here (opens new window), we provide to Ontop the following JDBC connection information in a ".properties file" for a Dremio instance running on the localhost:


Dremio JDBC driver can be downloaded from here (opens new window).

Over an OBDA setting containing the following mapping assertions:

:		http://example.org/voc#
ex:		http://example.org/
owl:		http://www.w3.org/2002/07/owl#
rdf:		http://www.w3.org/1999/02/22-rdf-syntax-ns#
xml:		http://www.w3.org/XML/1998/namespace
xsd:		http://www.w3.org/2001/XMLSchema#
foaf:		http://xmlns.com/foaf/0.1/
obda:		https://w3id.org/obda/vocabulary#
rdfs:		http://www.w3.org/2000/01/rdf-schema#
[MappingDeclaration] @collection [[
mappingId	uni1-student
target		:uni1/student/{s_id} a :Student ; foaf:firstName {first_name}^^xsd:string ; foaf:lastName {last_name}^^xsd:string . 
source		SELECT * FROM "uni1-student"
mappingId	uni1-attends
target		:uni1/student/{s_id} :attends :uni1/course/{c_id}/{title} .
source		SELECT "uni1-registration".s_id, "uni1-course".c_id, "uni1-course".title FROM "uni1-registration", "uni1-course" WHERE "uni1-registration".c_id = "uni1-course".c_id
mappingId	uni2-student
target		:uni2/student/{pid} a :Student ; foaf:firstName {fname}^^xsd:string ; foaf:lastName {lname}^^xsd:string . 
source		SELECT DISTINCT "uni2-person".pid, "uni2-person".fname, "uni2-person".lname FROM "uni2-person", "uni2-registration" WHERE "uni2-person".pid = "uni2-registration".pid
mappingId	uni2-attends
target		:uni2/student/{pid} :attends :uni2/course/{cid}/{course} .
source		SELECT "uni2-registration".pid, "uni2-course".cid, "uni2-course".course FROM "uni2-registration", "uni2-course" WHERE "uni2-registration".cid = "uni2-course".cid

Now we can execute the following SPARQL query on Ontop:

PREFIX : <http://example.org/voc#>
PREFIX foaf: <http://xmlns.com/foaf/0.1/>
SELECT DISTINCT ?course ?firstName ?lastName {
  ?student :attends ?course .
  ?student foaf:firstName ?firstName .
  ?student foaf:lastName ?lastName .

The results: