code: public void setRelativePath(QPath relPath) {
          if (relPath != null && relPath.isAbsolute()) {
              throw new IllegalArgumentException("relPath must be relative");
          }
          this.relPath = relPath;
      }
docs: Sets the relative path to the property in this relation.
  
  @param relPath the relative path to a property.
  @throws IllegalArgumentException if <code>relPath</code> is absolute.