5.2 Querying aligned corpora

This section explains how alignment information can be used as a filter in CQP queries.

• As a first example, let us consider the word nuclear power, which can be translated into German as Kernkraft, Kernenergie, Atomkraft or Atomenergie.

  > Nuke = "nuclear"%c "power"%c;

• Instead of manually perusing the translations of all 1417 hits, we can directly search for hits that contain one of the relevant words in the German translation.

  > "nuclear"%c "power"%c :EUROPARL-DE [lemma = "Kernkraft"];
> "nuclear"%c "power"%c :EUROPARL-DE [lemma = "Kernenergie "];
  etc.

  An alignment constraint consists of the marker :TARGET-CORPUS followed by an arbitrary query expression. CQP will scan the region aligned to each match of the main query and keep only those for which a match to the alignment constraint is found.

• The alignment constraint must be specified after the main query (including the within clause), but before a cut statement (which applies to the filtered query results). Multiple alignment constraints can be chained, in which case, they must all be satisfied.

• Alignment constraints can be negated by placing ! immediately after the marker. In this case, only those matches are kept for which the alignment constraint is not satisfied.

  > Other = "nuclear"%c "power"%c :EUROPARL-DE ! "(Kern|Atom).*";

  Can you figure out how nuclear power is translated in these examples?

• By chaining negated constraints, we can identify cases where the French translation is also different from the expected nucléaire:

  > "nuclear"%c "power"%c :EUROPARL-DE! "(Kern|Atom).*" :EUROPARL-FR! "nucleaire.*" %cd;

• An alignment constraint can never be satisfied for a match that has no translation in the target corpus, regardless of whether it is negated or not. Therefore,

  > "cats" :EUROPARL-FR ! [];

  returns no results at all. If you need to find unaligned instances of cats, you can only do so in a two-step process. Using the NQR AllCats and GoodCats (with translation) from above:

  > BadCats = diff AllCats GoodCats;
> size BadCats;

• Alignment constraints can only be added to regular CQP queries, not to MU queries (see Sec. 8.4).