public boolean isRequired() {
    return required;
  }
Abstract class to capture the three supported argument types for a table function: - Table
arguments - Descriptor arguments - SQL scalar arguments

<p>Each argument is named, and either passed positionally or in a `arg_name => value` convention.

<p>Default values are allowed for all arguments except Table arguments.
iotdb-api/udf-api/src/main/java/org/apache/iotdb/udf/api/relational/table/specification/ParameterSpecification.java