public void setDistanceMetric(String value) {
        verifyThat(distanceMetric == null, "already has distance-metric", distanceMetric);
        this.distanceMetric = value;
    }
This class holds the extracted information after parsing a
"attribute" block, using simple data structures as far as
possible.  Do not put advanced logic here!
@author arnej27959
config-model/src/main/java/com/yahoo/schema/parser/ParsedAttribute.java