FTAM/9000 Programmer's Guide

Chapter 1 31
HP FTAM/9000 Overview
Overview of FTAM Concepts
Overview of FTAM Concepts
This section takes a high-level approach to explaining concepts you
should know before writing FTAM applications. This section also refers
to specific FTAM functions. For detailed information regarding these
concepts and functions, refer to the Table of Contents for specific
chapters and sections.
The Virtual Filestore (VFS)
A real filestore uses a variety of mechanisms to structure, store, and
retrieve real files. For example, files on HP-UX systems are stored and
accessed as a stream of bytes; on other systems files might be stored and
accessed as fixed- or variable-length records, or in other ways.
To conceal these storage and access differences, the FTAM specification
defines a Virtual Filestore, or VFS. The VFS provides a uniform
interface to all real file systems. It uses a system-independent model for
describing files and their attributes. Though it represents real files, it
masks the system- dependent differences in style and structure. (Refer to
Figure 1-1.)
FTAM implementations map the VFS onto a real filestore. The mapping
function (from the open system to the real system) absorbs the style and
specification differences. You do not need to know the vendor, operating
system, or file system with which you want to communicate. You need
only know a file's complete name and where it is located. (However, you
may need to read the other vendor's PIC statement.)