The query language header is made of select-where and namespace definition.
The select statement applies to resources and properties, it is optionnal. By default, the matching of all the variables occurring in a query are returned from the retrieved annotations. A select operator allows to select the only variables whose matching are desired in the answers.
For instance, in the following example, we select only the title of the document and its authors.
select ?t c:author where ?x rdf:type c:Document ?x c:title ?t ?x c:author ?a