FTAM/9000 Programmer's Guide

Chapter 3 125
HP FTAM/9000 Data Structures
Ft_data_unit
Rules for Ft_data_unit Linked Lists (FTAM-2
Only)
The following rules apply to Ft_data_unit linked lists for FTAM-2
document types only.
• If you have an empty file, you must begin the linked list with a node
descriptor (not a data element).
• If a file already contains data, you may or may not have a node
descriptor, depending on whether you are starting a new FADU.
• Do not immediately follow a node descriptor with another node
descriptor.
You may, however, follow a data element with another data element
(i.e., node descriptors may have multiple data elements).
• You may submit an ft_sdata() request containing only a node
descriptor, though you must follow it with an ft_sdata() request that
starts with a data element.
• Do not use more than one node descriptor per ft_sdata() request.
• You must set node.arc_length to 1.
• You must set data_exists to TRUE since FADUs must contain data.