Availability Guide for Change Management

Making Application Subsystem Changes Online
Availability Guide for Change Management–125506
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Client/Server Computing and the Tandem
Application Environment
Users typically request information from server programs through an easy-to-use
graphical user interface (GUI) provided by the client program. The client/server
architecture is usually linked together by a local area network (LAN).
You can design client/server implementations of Tandem’s application environment
using products provided by Tandem. The Tandem client/server products, and how they
can be used with NonStop TS/MP, NonStop SQL/MP, and NonStop TM/MP, are
described later in this section.
Requester or Client Programs
Requester, or client, programs in a transaction-processing environment perform specific
tasks such as:
•
Handling input devices (for example, displaying a data entry screen, accepting input
data, and checking for input errors)
•
Sending input data in a special message format to the appropriate server
•
Processing the reply message returned by the server
Requesters are developed by application programmers as SCREEN COBOL programs,
Guardian programs, or—in the client/server environment—PC, Macintosh, or
workstation applications. (SCREEN COBOL is a programming language developed by
Tandem.)
Server Programs
Requester or client programs communicate with server programs. Servers perform the
following tasks:
•
Receive request messages from requesters
•
Perform the selected operations, such as database inquiries or updates
•
Return reply messages to requesters
A collection of replicated server processes is called a server class. A server class is a
group of server processes that perform a specific type of work. All server processes
within a server class run copies of the same server program. The replication of server
functions allows you to distribute the transaction workload across multiple processors.