Pathway/iTS TCP and Terminal Programming Guide

Introduction to TCP and Terminal Application
Programming
Compaq NonStop™ Pathway/iTS TCP and Terminal Programming Guide—426751-001
1-7
Pathway Applications
Pathway Applications
Pathway applications consist of two types of programs: requester programs and server
programs. This design allows application logic to be distributed near the resources it
manages. For example, presentation services are located near terminal devices or
workstations; database logic resides in server programs near that database. Requesters
and servers communicate by using the Guardian file system or the message system that
is part of the NonStop™ Kernel.
Users interact with your application by using devices and processes controlled by your
requester programs. Often these devices are terminals through which the users enter and
retrieve transaction data. They might also, however, be intelligent devices such as
personal computers, workstations, point-of-sale devices, or automatic teller machines
(ATMs). Or, they might be Guardian processes that provide transaction input from a
file or other batch medium.
Server processes receive requests from requester processes to access a database to add,
retrieve, or modify information. Server processes process request messages and send
reply messages with the results of the work on the database.
Servers and Server Classes
You can write Pathway server programs in C, C++, COBOL85, pTAL, TAL,
FORTRAN, or Pascal in the Guardian environment. Alternatively, you can write
Pathway server programs in C or COBOL85 in the Compaq NonStop™ Kernel Open
System Services (OSS) environment; you must program such servers to read the
Guardian $RECEIVE file as described in the Open System Services Programmer’s
Guide. In both cases, you configure and manage the servers using the PATHCOM
interactive interface or the Pathway management programming interface (based on the
Subsystem Programmatic Interface, or SPI) in the Guardian environment.
The same server programs, whether developed in the Guardian environment or in the
OSS environment, can be used with several different requester and client interfaces.
These interfaces include SCREEN COBOL, the Pathsend procedures, and the RSC/MP
interface.
The Pathway environment provides the feature of server classes. A server class is a
collection of replicated Pathway server processes. All server processes in a server class
provide the same set of functions; that is, they execute the same program.
Server Processes
Server processes provide the following benefits:
•
Server processes help ensure transaction integrity and, therefore, the integrity of the
database.
•
Server code can be reused by many requester programs, and you can separate
presentation services from database functions.
•
You can control which transactions can be performed on your node. You can
control the logic of the servers, database names, disk names, and so on.