title: UNION a subquery with sparql
body: <p>I am looking for an easy way to get the relations from all relations of a concept. For example:
  You search for a concept with the name "Abc". It has some relation to other objects, such as "D", "Ef", "Ghi". The result looks like:</p>
  
  <pre>-------------------------------------------------------------------------------
  | concept | relation      | value   |
  =====================================
  | uri:Abc | skos:narrower | uri:D   |
  | uri:Abc | skos:narrower | uri:Ef  |
  | uri:Abc | skos:broader  | uri:Ghi |
  -------------------------------------</pre>
  
  <p>So now you know the relations of "Abc". If you want to know the relations from the relations of "Abc" you can use a subselect. Such as the query below. But what I want is both of the results. I will know the relations of "Abc", but also from "D", "Ef", "Ghi".</p>
  
  <pre><code>SELECT (?v1 as ?concept) ?relation ?value WHERE
  {
      ?v1 ?relation ?value .
      {
          SELECT ?c1 ?r1 ?v1 WHERE 
          {
              ?c1 rdf:label "Abc" .
              ?c1 ?r1 ?v1 .
          }
      }
  }
  </code></pre>
  
  <p>This is my current query. In production I'm use a filter in it, but for this example it is not necessary.</p>