TS/MP 2.5 Pathsend and Server Programming Manual

possibly accessing different resource managers (HP NonStop SQL/MP and Enscribe) is known as
distributed transaction processing (DTP).
Pathway Applications
Pathway applications consist of two types of programs: requestor 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. Requestors 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 requestor
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 requestor 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, Pascal, TAL, pTAL, FORTRAN, or
Extended BASIC in the Guardian environment. Alternatively, you can write Pathway server programs
in C or COBOL85 in the 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 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 requestor and client interfaces. These interfaces
include SCREEN COBOL, the Pathsend procedures, the RSC/MP interface, and the POET.
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 requestor 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.
• In distributed environments, server processes provide high performance by allowing you to
use remote servers instead of performing multiple remote I/O operations, placing transaction
processing close to system resources.
server-classes
server-classes provide the following benefits:
• You can minimize use of system resources—for example, processes and file opens—because
server-classes are shared and highly utilized.
• You can maximize performance because server-classes allow multiple copies of server processes
to run concurrently in multiple processors.
20 Introduction to Pathway Application Programming