OSI/FTAM Programming Guide

ISO FTAM Concepts
HP NonStop OSI/FTAM Programming Guide—528612-001
2-23
Access Context
The model defines the access structure of a file. You can access the nodes of the tree
in order, starting from the root node and proceeding through the subtree under each
child node from left to right. You can access the nodes in each subtree in the same
order: the root node of the subtree, followed by the subtrees under each child node
from left to right. This order is called the preorder traversal sequence. Depending on
the constraint set defined for a file, you might also be able to access nodes in reverse
or random order.
Access Context
The actual data that your application can transfer depends on the access context. The
data transferred falls into two categories: structuring data elements, which delineate
the structure of the file, and file-contents data elements, which provide the contents of
the file. When you transfer a structured file without transferring the structuring data
elements (the node descriptors), the result is equivalent to an unstructured file.
A parameter called access-context, controls which structuring and file-contents
data elements are to be transferred. Actual access-context values for the document
types NonStop FTAM supports are addressed in Document Types on page 2-28 later in
this section.
Figure 2-5. Hierarchical File-Access Structure
VST0205.vsd
Root
NAME
DU
A
NAME
E
DU
Level 0
Level 1
B
DU
C
DU
D
F
DU
Level 2
Preorder traversal sequence: Root, A, B, C, D, E, F