A list of definitions that indicate what type of data you can
    store in the field and how Oracle Rdb uses that data. The field
    attributes include the data type and the following optional
    clauses:

    o  VALID IF

    o  MISSING_VALUE

    o  DATATRIEVE support clauses

 Do not use multiple, conflicting clauses in a field definition.

    For a complete description of field attributes, ask for HELP on
    Field_attr.