OSI/FTAM Programming Guide

ISO FTAM Concepts
HP NonStop OSI/FTAM Programming Guide—528612-001
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FTAM-3 Documents
between nodes, for example—is lost if the whole file is transferred in UA access
context. (The result is equivalent to an unstructured file.) Only the data contents of the
file are transferred in this case.
In the FA access context, structuring data elements in the form of node-descriptor data
elements are transferred, along with file-contents data elements. The file is transferred
as a sequence of node-descriptor data elements and file-contents data elements,
starting with node-descriptor data elements. The node-descriptor data elements mark
the beginning of data for each node in the structure. In this way, the structural
semantics of the file are preserved.
An FTAM-2 file is equivalent to an Enscribe relative file or SQL table, Type R, on the
NonStop system.
FTAM-3 Documents
FTAM-3 documents are unstructured binary files. They consist of a root node with a
data unit (which can be empty), but no node name. The data unit is composed of zero,
one, or more octet (byte) strings and has no size or length limitations.
Because an FTAM-3 document contains only one data unit, your application program
can access only the entire file. Therefore, you perform file-access operations on an
FTAM-3 document as a whole.
FTAM-3 files are limited to these actions: read, replace, extend, and erase. The locate
action is not possible. The only FADU identity used is first, which identifies the FADU
corresponding to the root node.
Only one access context, unstructured all-data units (UA), can be used with FTAM-3
files. In the UA access context, only file-contents data elements are transferred. (The
concept of structuring data elements does not apply to an unstructured file.) This
means that only the data contents of the file are transferred for FTAM-3 files.
An FTAM-3 file is equivalent to an entry-sequenced or unstructured binary file on the
NonStop system, depending on the string-significance defined for the file. The concept
of string-significance is described below.
Describing Document Contents
ISO specifies parameters that further define an FTAM document type, as follows:
•
universal-class determines what character string types are allowed. ISO 8824
defines these character string types. (These character string types are described in
greater detail in the OSI/FTAM Programming Reference Manual.)
•
maximum-string-length defines the maximum length of a character string that
can be transferred as a data element of a file.
•
string-significance determines whether strings contribute to the file semantics, or
whether the division of the file into strings is arbitrary and need not be preserved
during a transfer. The string-significance parameter can take on the values