Question

Glad if someone can clarify.

I always read that SQL and SPARQL are very similar.
However, a lot of times i have seen sparql query without the FROM keyword.
You would assume that you have to query the datasource ‘FROM’ somewhere in the database
like how SQL behaves.

Example

PREFIX foaf:  <http://xmlns.com/foaf/0.1/>
SELECT ?name
WHERE 
{
    ?person foaf:name ?name .
}

How does it know where to look for? Like in SQL, look in Database1 – table1

Cheers

Answer 1

SPARQL queries are execute against an RDF dataset, which has two parts:

• A single default graph: a set of triples with no name attached to them
• Zero or more named graphs: a set of triples identified by a name

You can specify the graph to query using the optional FROM or FROM NAMED clauses. Have a look at Specifying RDF Datasets. If you omit those clauses, then the query is executed on the default graph.

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Graphs and RDF dataset storage is implementation dependent. For example, using Jena ARQ you use a QueryExecutionFactory and you can initialize it in two ways:

• passing a Model, which becomes the default graph on which queries are executed
• passing a Dataset, which can contain a single default graph and several named graphs

Code Examples for Jena ARQ are available here. Other implementation may be different.