ch04

Chapter 4 - grlc: API automation by query sharing

• Examples
• Exercises

Examples

1. Querying list of band, album and genre from DBpedia - SPARQL

PREFIX rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#>
PREFIX dbo: <http://dbpedia.org/ontology/>
PREFIX schema: <http://schema.org/>

SELECT ?band ?album ?genre WHERE {
  ?band rdf:type dbo:Band .
  ?album rdf:type schema:MusicAlbum .
  ?band dbo:genre ?genre .
  ?album dbo:artist ?band .
} LIMIT 100

2. Querying list of rock bands and albums from DBpedia - SPARQL

PREFIX rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#>
PREFIX dbo: <http://dbpedia.org/ontology/>
PREFIX schema: <http://schema.org/>

SELECT ?band ?album WHERE {
  ?band rdf:type dbo:Band .
  ?album rdf:type schema:MusicAlbum .
  ?band dbo:genre <http://dbpedia.org/resource/Rock_music> .
  ?album dbo:artist ?band .
} LIMIT 100

3. Querying list of alternative bands and albums from DBpedia - SPARQL

PREFIX rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#>
PREFIX dbo: <http://dbpedia.org/ontology/>
PREFIX schema: <http://schema.org/>

SELECT ?band ?album WHERE {
  ?band rdf:type dbo:Band .
  ?album rdf:type schema:MusicAlbum .
  ?band dbo:genre
            <http://dbpedia.org/resource/Alternative_rock> .
  ?album dbo:artist ?band .
} LIMIT 100

4. Querying list of bands and albums from DBpedia from a specified genre - SPARQL

PREFIX rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#>
PREFIX dbo: <http://dbpedia.org/ontology/>
PREFIX schema: <http://schema.org/>

SELECT ?band ?album WHERE {
  ?band rdf:type dbo:Band .
  ?album rdf:type schema:MusicAlbum .
  ?band dbo:genre ?_genre_iri .
  ?album dbo:artist ?band .
} LIMIT 100

Exercises

1. Create an API that retrieves all bands from DBpedia. Solution: SPARQL

#+ summary: Lists all DBpedia dbo:Band
#+ endpoint: http://dbpedia.org/sparql
#+ method: GET

PREFIX dbo: <http://dbpedia.org/ontology/>

SELECT DISTINCT ?s
WHERE {
  ?s a dbo:Band
}

2. Create an API that lists bands that play either Rock or Jazz, and that have either Liverpool or Los Angeles as hometown. Solution: SPARQL

• Tip 1: Use the DBpedia ontology types dbo:genre and dbo:hometown.
• Tip 2: Use the grlc enumerate decorator.

#+ summary: Bands by city and genre
#+ endpoint: http://dbpedia.org/sparql
#+ tags:
#+   - dbpedia
#+ method: GET
#+ enumerate:
#+   - genre:
#+      - http://dbpedia.org/resource/Rock_music
#+      - http://dbpedia.org/resource/Jazz
#+   - hometown:
#+      - http://dbpedia.org/resource/Liverpool
#+      - http://dbpedia.org/resource/Los_Angeles

PREFIX dbo: <http://dbpedia.org/ontology/>
SELECT DISTINCT ?s
WHERE {
  ?s a dbo:Band;
  dbo:genre ?_genre_iri;
  dbo:hometown ?_hometown_iri
}

3. Expand the API from the previous exercise by adding documentation and making sure your query can only be run on DBpedia SPARQL endpoint. Solution: SPARQL

• Tip: Use the summary, description, endpoint and endpoint_in_url decorators.

#+ summary: Bands by city and genre
#+ description:
#+   This API endpoint lists bands from DBPedia that play either
#+   Rock or Jazz, and that have either Liverpool or Los Angeles as hometown.
#+ endpoint: http://dbpedia.org/sparql
#+ endpoint_in_url: false
#+ tags:
#+   - dbpedia
#+ method: GET
#+ enumerate:
#+   - genre:
#+      - http://dbpedia.org/resource/Rock_music
#+      - http://dbpedia.org/resource/Jazz
#+   - hometown:
#+      - http://dbpedia.org/resource/Liverpool
#+      - http://dbpedia.org/resource/Los_Angeles

PREFIX dbo: <http://dbpedia.org/ontology/>
SELECT DISTINCT ?s
WHERE {
  ?s a dbo:Band;
  dbo:genre ?_genre_iri;
  dbo:hometown ?_hometown_iri
}

4. Create an API that lists the name, genre and hometown of bands whose name matches a given string. Solution: SPARQL

• Tip 1: Use the DBpedia property type dbp:name.
• Tip 2: Because DBpedia uses Virtuoso, you can use the built in function bif:contains.

#+ summary: Bands by city and genre
#+ description:
#+   This API endpoint lists bands from DBPedia that play either
#+   Rock or Jazz, and that have either Liverpool or Los Angeles as hometown.
#+ endpoint: http://dbpedia.org/sparql
#+ endpoint_in_url: false
#+ tags:
#+   - dbpedia
#+ method: GET

PREFIX dbo: <http://dbpedia.org/ontology/>
PREFIX dbp: <http://dbpedia.org/property/>
PREFIX bif: <bif:>

SELECT DISTINCT ?name ?genre ?hometown
WHERE {
?s a dbo:Band;
  dbp:name ?name;
  dbo:genre ?genre;
  dbo:hometown ?hometown .
  ?name bif:contains ?_bandname
} LIMIT 100