SPARQLqueries

What is SPARQL?

SPARQL is a powerful query language for exploring semantic web data in RDF format. RDF data consists of statements in the form of triples: subject-predicate-object. SPARQL queries leverage these triple patterns to extract meaningful insights from vast knowledge graphs.

Consider three programming languages stored in a database with unique identifiers:

<https://example.com/C>
<https://example.com/C++>
<https://example.com/Python>

We use angle brackets to embed identifiers. With a relationship called IsA, we can express statements like "C is a Programming Language" that machines can understand and query.

<https://example.com/C> <https://example.com/IsA> <https://example.com/ProgrammingLanguage>
<https://example.com/C++> <https://example.com/IsA> <https://example.com/ProgrammingLanguage>
<https://example.com/Python> <https://example.com/IsA> <https://example.com/ProgrammingLanguage>

Your First SPARQL Query

Now let's query this data. What if we want to ask: "Give me all the programming languages"?

SELECT ?proglang {
  ?proglang <https://example.com/IsA> <https://example.com/ProgrammingLanguage>
}

The variable ?proglang will match all entities that satisfy this pattern. Using the PREFIX keyword, we can simplify our queries:

PREFIX example: <https://example.com/>

SELECT ?type {
  example:C++ example:IsA ?type
}

Real-World Data with Wikidata

To demonstrate SPARQL with real-life data, we use Wikidata — an open knowledge base containing information across countless domains. Wikidata provides a dedicated SPARQL endpoint where you can run queries and see live results.

PREFIX wdt: <http://www.wikidata.org/prop/direct/>
PREFIX wd: <http://www.wikidata.org/entity/>

SELECT ?proglang {
  ?proglang wdt:P31 wd:Q9143
}

Adding more triple patterns lets us retrieve additional properties. Here we get programming languages along with their inception dates:

SELECT ?proglang ?year {
  ?proglang wdt:P31 wd:Q9143;
            wdt:P571 ?year.
}

Quick Examples

Filtering Results

Use FILTER to narrow down results based on conditions:

SELECT ?proglang ?year {
  ?proglang wdt:P31 wd:Q9143;
            wdt:P571 ?year.
  FILTER (year(?year) > 2000)
}

Counting Results

Aggregate functions let you analyze your data:

SELECT (COUNT(?proglang) AS ?count) {
  ?proglang wdt:P31 wd:Q9143.
}

Asking Questions

Use ASK to verify if data exists:

ASK {
  ?proglang wdt:P31 wd:Q9143;
            wdt:P571 ?year.
}

Federated Queries

Combine data from multiple sources using SERVICE:

SELECT ?proglang ?resource ?homepage {
  ?proglang wdt:P31 wd:Q9143.

  SERVICE <http://dbpedia.org/sparql> {
    ?resource rdf:type wd:Q9143;
              owl:sameAs ?proglang;
              foaf:homepage ?homepage.
  }
}
LIMIT 10