Query wikipedia links

Question

I'm using the following query to receive label and description of all Wikidata-entries with geo-location in a geo-bounding box:

SELECT DISTINCT ?place ?placeLabel ?placeDescription ?location WHERE
{
  SERVICE wikibase:box
  {
    ?place wdt:P625 ?location.
    bd:serviceParam wikibase:cornerWest 'Point({0} {1})'^^geo:wktLiteral.
    bd:serviceParam wikibase:cornerEast 'Point({2} {3})'^^ geo:wktLiteral.
  }
  SERVICE wikibase:label { bd:serviceParam wikibase:language '{4},en,fr,es'. }
  ?place(wdt:P31/wdt:P279*) wd:Q618123.
}

This works fine, but now I would like to also have the link to the wikipedia article included in the result. I tried to modify the query to:

SELECT DISTINCT ?place ?placeLabel ?placeDescription ?location ?article WHERE

but it doesn't work, articles are not returned. Any idea, how this works?

Edit: after all the useful hints from you guys, here is the version, which works fine now:

SELECT DISTINCT ?place ?placeLabel ?placeDescription ?location ?article WHERE
{
  SERVICE wikibase:box
  {
     ?place wdt:P625 ?location.
     bd:serviceParam wikibase:cornerWest 'Point({0} {1})'^^geo:wktLiteral.
     bd:serviceParam wikibase:cornerEast 'Point({2} {3})'^^ geo:wktLiteral.
  }
  SERVICE wikibase:label
  { 
      bd:serviceParam wikibase:language '[AUTO_LANGUAGE],en,fr,es,{4}'. 
      ?place schema:description ?placeDescription ; rdfs:label ?placeLabel. 
  }
  # all places with a location
  ?place(wdt:P31/wdt:P279*) wd:Q618123.

  # include wikipedia links
  ?article schema:about ?place.
  FILTER REGEX(STR(?article), '.wikipedia.org/wiki/').

  # optional, only places containing string in label
  FILTER CONTAINS(lcase(?placeLabel), '{5}').
}

Answer 1

The query service does not know that your variable ?article means that you want a Wikipedia article. You have to also ask for it in the actual query. One way to do that is to add these lines in the query:

?article schema:about ?place.
FILTER REGEX(STR(?article), ".wikipedia.org/wiki/") .

The first line queries for all the the sitelinks that the item have. The second one filters out those that go to other projects than Wikipedia, for instance Wikimedia Commons. So here is an example that might work for you:

SELECT DISTINCT ?place ?placeLabel ?placeDescription ?location WHERE
{
  SERVICE wikibase:box
  {
    ?place wdt:P625 ?location.
    bd:serviceParam wikibase:cornerWest 'Point({0} {1})'^^geo:wktLiteral.
    bd:serviceParam wikibase:cornerEast 'Point({2} {3})'^^ geo:wktLiteral.
  }
  SERVICE wikibase:label { bd:serviceParam wikibase:language '{4},en,fr,es'. }
  ?place(wdt:P31/wdt:P279*) wd:Q618123.
  ?article schema:about ?place.
  FILTER REGEX(STR(?article), ".wikipedia.org/wiki/") .
}