hectorcorrea/fuseki_demo

Notes on playing with Apache Jena Fuseki

Apache Jena or Apache Jena Fuseki

Apache Jena is a Java API for semantic web applications. It is a set packages that you can reference from within Java applications. https://jena.apache.org/tutorials/rdf_api.html#ch-Jena%20RDF%20Packages

Apache Jena Fuseki on the other hand is an SPARQL Server that runs on top of Jena and makes Jena functionality available to applications via HTTP.

Download

Download Apache Jena Fuseki from https://jena.apache.org/download/index.cgi upzip it and run the server

cd Downloads/apache-jena-fuseki-2.3.1
./fuseki-server

Browse to http://localhost:3030 and you can play with the user interface.

A first example

With the Fuseki Server running, add a few triples to it

curl -X POST -d @the_raven.n3 localhost:3030/datasetone/update

...and then query them

curl -X POST -d "query=select ?s where { ?s ?p ?o . }" localhost:3030/datasetone/query

... you can also query the triples from the web page at http://localhost:3030/dataset.html?tab=query&ds=/datasetone

select ?s ?p ?o
where { ?s ?p ?o . }

Adding more data

Add the data in the data.n3 file

curl -X POST -d @data.n3 localhost:3030/datasetone/update

we will use this data in the rest of the examples.

Querying with SPARQL

Browse to http://localhost:3030/dataset.html?tab=query&ds=/datasetone and enter the following query:

select ?s ?p ?o
where { ?s ?p ?o }

This will return all the predicates and their values for all the subjects.

To fetch only the data for a single subject:

select ?s ?p ?o
where { <http://demo/zoia> ?p ?o }

To all the predicates for the the subjects:

select ?p
where { ?s ?p ?o }

Use the distinct clause if you want unique values

select distinct ?p
where { ?s ?p ?o }

Let's all go to the movies

The movie data as well as the queries used in these examples were based on Chapter 4 of the Semantic Web for the Working Ontologist.

Find all movies where James Dean played a role.

select ?movie
where { <http://demo/jamesDean> <http://test/predicates/playedIn> ?movie }

Find all James Dean's movies and their directors (notice that there is no comma in between variables in the select!)

select ?movie ?director
where {
  <http://demo/jamesDean> <http://test/predicates/playedIn> ?movie .
  ?movie <http://test/predicates/directedBy> ?director .
}

Find all actresses that played with James Dean

select ?actress ?movie
where {
  <http://demo/jamesDean> <http://test/predicates/playedIn> ?movie .
  ?actress <http://test/predicates/playedIn> ?movie .
  ?actress <http://test/predicates/type> <http://demo/woman> .
}

Inferencing

Find all animals, the ones marked directly as animals and the ones that marked as something that is a subclass of an animal.

prefix rdfs: <http://www.w3.org/2000/01/rdf-schema#>

select ?something
where {?class rdfs:subClassOf* <http://demo/animal> .
  ?something a ?class .
}

Gotchas

If you add a value with a type, for example if the value of "Zoia Horn" was entered as

"Zoia Horn"^^<http://www.w3.org/2001/XMLSchema#string>

you must use the value with the type when you search for it.

select ?s
where { ?s ?p "Zoia Horn"^^<http://www.w3.org/2001/XMLSchema#string> }

More SPARQL queries

Query with OPTIONAL

# all triples of type person and their age
# only returns people with an age
select ?s ?age
where {
  ?s a <http://demo/person> .
  ?s <http://test/predicates/age> ?age .
}


# all triples of type person and their age
# returns all people (and the age for those that have one)
# similar to an OUTER JOIN in SQL
select ?s ?age
where {
  ?s a <http://demo/person> .
  OPTIONAL { ?s <http://test/predicates/age> ?age . }
}

Query with GROUP, COUNT, and HAVING

select ?blogger
where {
  ?blogger a <http://demo/blogger> .
  ?blog <http://test/predicates/author> ?blogger .
  ?blog <http://test/predicates/title> ?title .
}
group by ?blogger
having (count(?blog) > 2)

Note: UNSAID is not supported.

Using CONSTRUCT to generate graphs (instead of lists)

construct {
  ?blogger <http://demo/published> ?title .
}
where {
  ?blogger a <http://demo/blogger> .
  ?blog <http://test/predicates/author> ?blogger .
  ?blog <http://test/predicates/title> ?title .
}

hectorcorrea / fuseki_demo