A member of the BaseRecordLayout substitution group intended for use when the data items are stored in an external proprietary format. In addition to the link to the PhysicalStructure provided by BaseRecordLayout, the record layout is this namespace (m4) identifies the character set and array base for the external data, identifies the software of the proprietary system, provides a description of how the data item is addressed within the system, provides default values for numeric data types, text data types, dateTime data types, whether coded data should be treated as numeric or text, a default variable scheme, proprietary information, and a full description of each data item including its link to the variable description and system address.