Using prefixe foaf when creating Ontop mappings.

[Vidar Norstein Klungre]

Hello.

I have a setup where I have imported the foaf ontology in Protege, and I want to use concepts from foaf when creating mappings between my MySQL database and the foaf:Person concept. I'm pretty sure foaf is imported correctly, and I have defined the foaf prefix, but I'm not able to use it when creating mappings manually.

The mapping I try to make looks like this, but it is not accepted by Ontop.

<Person-{p_id}> a foaf:Person .

In particular, it does not recognize foaf:Person.

I have also tried the following mapping templates with no luck:

@prefix foaf: <http://xmlns.com/foaf/0.1/> .
<Person-{p_id}> a foaf:Person .

and 

<Person-{p_id}> a <http://xmlns.com/foaf/0.1/Person> .

However Ontop accepted my custom made class called Myperson, so the problem is indeed with the foaf Person class:

<Person-{p_id}> a :Myperson .

So is it something wrong with the mapping templates I have tried, or have I not been able to import the foaf ontology correctly? For more details, I have added screenshots, and more details below.

Best regards, Vidar Klungre

Detailed workflow:

0. Set up a MySQL database.

1. After importing the ontology into Protege (using Ontology imports), I got an error: "URI Scheme not file". This is obviously not good, but after pressing ok, everything looked fine. I also added an ontology prefix in the Active ontology tab. 

Prefix: foaf

Value http://xmlns.com/foaf/0.1/

2. Checking the Class tab, and yes, all the foaf concepts are there, including the Person concept I want to use.

3. Go to the ontop mappings tab, and set up a data source.

4. ontop mappings tab -> mapping manager -> create new mapping. Setting SQL query to "select * from ex1", which returns my data. Good. I try to the following mapping templates:

<Person-{p_id}> a foaf:Person .

Result: Not accepted

Error message: "ERROR: The below list of predicates is unknown to the ontoogy: - nullPerson"

Comment: I expected this to work, given the fact that I have defined the foaf prefix in Protege.

@prefix foaf: <http://xmlns.com/foaf/0.1/> .
<Person-{p_id}> a foaf:Person .

Result: Not accepted

Error message: "ERROR: The below list of predicates is unknown to the ontoogy: - http://xmlns.com/foaf/0.1/Person"

Comment: Testing if I added the prefix also inside the mapping template.

<Person-{p_id}> a <http://xmlns.com/foaf/0.1/Person> .

Result: Not accepted

Error message: "ERROR: The below list of predicates is unknown to the ontoogy: - http://xmlns.com/foaf/0.1/Person"

Comment: Testing if it worked when writing the full path.

<Person-{p_id}> a :Myperson .

Result: Accepted.

Comment: This was to confirm that the object is the problem.

[Benjamin Cogrel]

Hello Vidar,

xmlns.com is currently down so I cannot import the ontology from Protege.

However, I added manually the foaf:Person class (by giving its URL), added the prefix foaf as you did in the "Ontology prefixes" tab and I was able to write mappings like you did:

<Person-{p_id}> a foaf:Person .

While this mapping is not rejected, I suggest you to use a CURIE instead of a relative IRI:
:Person-{p_id} a foaf:Person .

Best regards,
Benjamin

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