FTAM/9000 Programmer's Guide

446 Chapter 11
Document Types and Constraint Sets
Constraint Sets
Additional constraints on the Sequential Flat constraint set are as
follows:
End of File No node selected. FT_PREVIOUS gives last node in
sequence; FT_CURRENT and FT_NEXT give an error
Read Whole File Read in access context FA or UA with FADU identity of
FT_BEGIN
Write Whole File Transfer the series of leaf FADUs which would be generated
by reading the whole file in access context FA; perform the
transfer with a FADU identity of FT_END and an
FT_FA_INSERT file access action
Structural Constraints The root node does not have an associated data unit. All
children of the root node are leaf nodes and have an associated
data unit. All arcs from the root node are of length one.
Action Constraints You can use FT_FA_INSERT only at the end of a file, with
FADU identity set to FT_END. The location following an
FT_FA_INSERT action is FT_END. You can erase only at the
root node to empty the file, with FADU identity set to
FT_BEGIN. The result is a solitary root node without an
associated data unit.
Identity Constraints The FADU identity associated with the file action is FT_BEGIN,
FT_END, FT_FIRST, or FT_NEXT. The allowable actions are as
follows.
FT_FA_LOCATE Actions are valid for each FADU identity
on the whole file and on all leaf nodes.
FT_FA_READ Actions are valid for the whole file at
FT_BEGIN. Actions are valid for leaf
nodes at FT_FIRST and FT_NEXT.
Actions are not valid at FT_END.
FT_FA_INSERT Actions are valid on the leaf node with the
FT_END FADU identity.
FT_FA_ERASE Actions are valid on the whole file only
with the FT_BEGIN FADU identity.