Hynotized by Fuseki

No, this is indeed not a song title (at least, that's what Mr. Google said!). Basically, what I am trying to do is to build (reuse, to be exact) a federated query server for my project. And thanks God, I've found Fuseki!

But, wait a minute, what's exactly federated query mean? Well, literally, federated query means you send queries over a couple of remote endpoints and then aggregate the query results. I know of two ways to do this by using Named Graphs; and SERVICE keyword, in which I am gonna explore now.

And then? So, assume that I own three companies; Company A, Company B, and Company C. Each of these companies already supports Semantic Web technologies (because they're my companies!), therefore each of them has a SPARQL endpoint for querying datasets. But the problem is, I want to do a query for them all at once, for example, I wanna get a list of employees from my companies, along with their job position. Well, easy peasy then, here's the query:

	prefix ex: <http://example.com/ex/0.1/>
	prefix foaf: <http://xmlns.com/foaf/0.1/>
	SELECT ?name ?role ?companyname
	{
	?ds ex:endpoint ?ep .
	SERVICE ?ep {
	?person foaf:name ?name .
	?person ex:role ?role .
	?person ex:company ?company .
	?company foaf:name ?companyname
	}
	} ORDER BY ASC(?companyname)

view raw federated-query-service.sparql hosted with ❤ by GitHub

But, wait, did you notice that I just utilized a variable for substituting the SERVICE URIs? Yes I did! In order to run that query, I must specify what SERVICE URIs to be queried federately. It means I should write an RDF file containing data about SPARQL endpoints for all my companies, and then load it into my SPARQL server. So, check out the following RDF file then!

	<rdf:RDF
	xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
	xmlns:rdfs="http://www.w3.org/2000/01/rdf-schema#"
	xmlns:ex="http://example.com/ex/0.1/">
	<ex:Dataset rdf:about="http://a.com/foaf.rdf#dataset">
	<ex:endpoint rdf:resource="http://localhost:4040/lab/query"/>
	</ex:Dataset>
	<ex:Dataset rdf:about="http://b.com/foaf.rdf#dataset">
	<ex:endpoint rdf:resource="http://localhost:5050/lab/query"/>
	</ex:Dataset>
	<ex:Dataset rdf:about="http://c.com/foaf.rdf#dataset">
	<ex:endpoint rdf:resource="http://localhost:6060/lab/query"/>
	</ex:Dataset>
	</rdf:RDF>

view raw companies-endpoints.rdf hosted with ❤ by GitHub

OK then, now I could execute my sacred, holy, and precious federated query! After that, I got the following result:

If you're curious what's inside the datasets from each company, check this stuff out then (actually, I concat them all on the code below).

	//Company A
	<rdf:RDF
	xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
	xmlns:rdfs="http://www.w3.org/2000/01/rdf-schema#"
	xmlns:foaf="http://xmlns.com/foaf/0.1/"
	xmlns:ex="http://example.com/ex/0.1/">
	<foaf:Person rdf:about="http://a.com/foaf.rdf#fariz-darari">
	<foaf:name>Fariz Darari</foaf:name>
	<foaf:title>Mr</foaf:title>
	<ex:company rdf:resource="http://a.com/foaf.rdf#company" />
	<ex:role>CEO</ex:role>
	</foaf:Person>
	<foaf:Person rdf:about="http://a.com/foaf.rdf#syahrini">
	<foaf:name>Syahrini</foaf:name>
	<foaf:title>Ms</foaf:title>
	<ex:company rdf:resource="http://a.com/foaf.rdf#company" />
	<ex:role>Secretary</ex:role>
	</foaf:Person>
	<ex:Company rdf:about="http://a.com/foaf.rdf#company">
	<foaf:name>Company A</foaf:name>
	</ex:Company>
	</rdf:RDF>
	//Company B
	<rdf:RDF
	xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
	xmlns:rdfs="http://www.w3.org/2000/01/rdf-schema#"
	xmlns:foaf="http://xmlns.com/foaf/0.1/"
	xmlns:ex="http://example.com/ex/0.1/">
	<foaf:Person rdf:about="http://b.com/foaf.rdf#budi-susilo">
	<foaf:name>Budi Susilo</foaf:name>
	<foaf:title>Mr</foaf:title>
	<ex:company rdf:resource="http://b.com/foaf.rdf#company" />
	<ex:role>Janitor</ex:role>
	</foaf:Person>
	<foaf:Person rdf:about="http://b.com/foaf.rdf#gayus">
	<foaf:name>Gayus</foaf:name>
	<foaf:title>Mr</foaf:title>
	<ex:company rdf:resource="http://b.com/foaf.rdf#company" />
	<ex:role>Debt Collector</ex:role>
	</foaf:Person>
	<ex:Company rdf:about="http://b.com/foaf.rdf#company">
	<foaf:name>Company B</foaf:name>
	</ex:Company>
	</rdf:RDF>
	//Company C
	<rdf:RDF
	xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
	xmlns:rdfs="http://www.w3.org/2000/01/rdf-schema#"
	xmlns:foaf="http://xmlns.com/foaf/0.1/"
	xmlns:ex="http://example.com/ex/0.1/">
	<foaf:Person rdf:about="http://c.com/foaf.rdf#ani">
	<foaf:name>Ani</foaf:name>
	<foaf:title>Mrs</foaf:title>
	<ex:company rdf:resource="http://c.com/foaf.rdf#company" />
	<ex:role>CEO</ex:role>
	</foaf:Person>
	<foaf:Person rdf:about="http://c.com/foaf.rdf#bambang">
	<foaf:name>Bambang</foaf:name>
	<foaf:title>Mr</foaf:title>
	<ex:company rdf:resource="http://c.com/foaf.rdf#company" />
	<ex:role>CTO</ex:role>
	</foaf:Person>
	<ex:Company rdf:about="http://c.com/foaf.rdf#company">
	<foaf:name>Company C</foaf:name>
	</ex:Company>
	</rdf:RDF>

view raw company-dataset.rdf hosted with ❤ by GitHub