code: @Override
  	public DataSet get(ResourceSnapshot resource) throws UnknownResourceException {
  		DataSet dataSet = this.resources.get(resource.name());
  		if(dataSet==null) {
  			throw new UnknownResourceException("Unknown resource '"+resource.name()+"'");
  		}
  		return dataSet;
  	}
docs: {@inheritDoc}
  @throws UnknownResourceException if the resource is not known.