3.2 SPARQL basics | Semantic Web

YASGUI application¶

YASGUI is an application for easily using SPARQL endpoints, it can be accessed at http://yasgui.org/

Get acquainted with the tool and submit the example query to DBpedia. Yasgui is a useful tool for writing SPARQL queries. It is recommended that you try your queries first using Yasgui before submitting them.

SPARQL ASK¶

SPARQL ASK can be used to test if a certain query pattern exists or not.

WarSampo (Sotasampo in Finnish) contains large amounts of information about World War 2 in Finland. The data is published on a SPARQL endpoint at http://ldf.fi/warsa/sparql, and there is also a web portal that provides several web user interfaces to different WarSampo datasets.

A+ presents the exercise submission form here.

SPARQL DESCRIBE¶

Query the WarSampo endpoint for the description of the resource with the English label “Winter War” using SPARQL DESCRIBE. Expand the DESCRIBE query to also return descriptions of all resources to which there is a link from (any predicate connecting to) the Winter War resource.

In the following exercises, DESCRIBE queries can be useful to inspect how a resource is described.

Simple SPARQL SELECT¶

Using the WarSampo SPARQL endpoint, create a query that returns the URIs of 10 photographs (class http://ldf.fi/schema/warsa/Photograph), from which there is a direct relation to C.G.E. Mannerheim, the commander-in-chief of Finland’s armed forces (skos:prefLabel “Carl Gustaf Emil Mannerheim”).

The relation (property http://www.cidoc-crm.org/cidoc-crm/P138_represents) indicates that the person is automatically recognized as a named entity in the photograph’s metadata description. This usually means that the person is in the photograph, or somehow else involved in the photography event.

For instance, ?sub http://www.cidoc-crm.org/cidoc-crm/P138_represents ?obj inside a SPARQL WHERE clause to WarSampo endpoint would retrieve all triples that describe named entities being in a photograph’s description.

Remember to test your query in YASGUI before submitting your answer.

Also remember to limit your query to 10 results with SPARQL LIMIT clause. Besides helping you get the tests correct, it will make testing your queries in YASGUI much faster if the result set isn’t large.

Note: The tests don’t access all WarSampo data, thus you might get empty results from tests even though YASGUI returns some results or even the correct ones. This means there is something likely irrelevant in the query.

A+ presents the exercise submission form here.

BROKEN SPARQL¶

The following SPARQL queries have several errors. Fix the queries so that they work. For each query submit the result the fixed query provides.

You must also SUBMIT the fixed QUERIES. You can submit the queries as a single file after answering the query specific questions. If you don’t submit the queries, any points given by correct query results might be removed.

In this section we make use of aggregates. SPARQL aggregates work similary to SQL aggregates. Here are the available SPARQL Aggregates and a few examples: https://en.wikibooks.org/wiki/SPARQL/Aggregate_functions.

Hint: You might have noticed it already, but the editor in YASGUI tries to help you! If it detects a syntax error, the erroneus line lights up red and hovering your mouse over the exclamation mark on the left side on the row shows you feedback on the error.

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The following query tries to retrieve the MRR-number (Mannerheim-ristin ritarit, Mannerheim Cross) of C.G.E. Mannerheim.

PREFIX : <http://ldf.fi/schema/warsa/>
PREFIX skos: <http://www.w3.org/2004/02/skos/core#>

SELECT ?mrr
WHERE
  ?person <http://ldf.fi/schema/warsa/actors/knight> mrr ;
              skos:prefLabel ?label .
  FILTER (?label != "Carl Gustaf Emil Mannerheim")
}

This query tries to count how many events C.G.E. Mannerheim has participated in in the WarSampo dataset.

PREFIX crm: <http://www.cidoc-crm.org/cidoc-crm/>

SELECT (COUNT (DISTINCT ?event) as ?event_count)
WHERE {
  ?event crm:P11_had_participant ?person .
  ?person skos:prefLabel ?name_label .
  FILTER SELECT(?label = "Carl Gustaf Emil Mannerheim")
}

Now, submit the fixed queries.

A+ presents the exercise submission form here.

SPARQL Aggregates¶

Modify the query from the previous exercise to show who are represented (property http://www.cidoc-crm.org/cidoc-crm/P138_represents) in the same photographs as C.G.E. Mannerheim. Create a query that will return the names of the 10 people who are most often represented in the same photographs as Mannerheim, along with the number of photographs the person is represented in with Mannerheim.

Note: The automated tests might not work properly when using HAVING operator. FILTER works well as an alternative. Also, grouping by photo count breaks the tests. On the GROUP BY line avoid the syntax “GROUP BY(?variable)” as the automatic tests don’t work with that syntax. Use instead syntax without parentheses like this “GROUP BY ?variable”.

Grouping by aggregated variable (like photo count here) will break the tests in later assignments as well.

A+ presents the exercise submission form here.

Visualizing SPARQL results with YASGUI¶

Using YASGUI and the SPARQL endpoint of DBpedia (https://dbpedia.org/sparql), visualize how many people described in DBpedia have been born (dbo:birthPlace) in each Finnish city or town. Finnish cities and towns have a dct:subject relation to dbc:Cities_and_towns_in_Finland. Create a pie chart visualization, which can be found in YASGUI by clicking Chart → Configure → Charts → Pie → Select your preferred pie chart. Include only the 20 cities with the largest amount of known people born in them, and use the English labels for cities.

YASGUI should automatically define the prefixes dct and dbc when you write them, or you can manually define them with:

PREFIX dbc: <http://dbpedia.org/resource/Category:>
PREFIX dct: <http://purl.org/dc/terms/>

SPARQL basics¶

YASGUI application¶

SPARQL ASK¶

SPARQL DESCRIBE¶

Simple SPARQL SELECT¶

BROKEN SPARQL¶

SPARQL Aggregates¶

Visualizing SPARQL results with YASGUI¶