code: public String getStringAttribute(boolean runtime, String attributeName, Address address) throws Exception {
          return getAttribute(runtime, attributeName, address).asString();
      }
docs: Convienence method that allows you to obtain a single attribute's string value from
  a resource.
  
  @param runtime if <code>true</code>, the attribute to be retrieved is a runtime attribute
  @param attributeName the attribute whose value is to be returned
  @param address identifies the resource
  @return the attribute value
  
  @throws Exception if failed to obtain the attribute value