public static Ranker getRankerByParameter(RankerType rankerType, Index indexer) {
			switch(rankerType){
			case COSINE:
				return new RankerCosine(indexer);
			case QL:
				return new RankerQL(indexer);
			case PHRASE:
				return new RankerPhrase(indexer);
			case LINEAR:
				return new RankerLinear(indexer);
			case NUMVIEWS:
				return new RankerNumviews(indexer);
			case NONE:
				return new RankerSimple(indexer);
			default:
				// Do nothing.
			}
			return null;
		}