Introduction to Data Management

Developing Applications With PATHWAY
6-4 15873 Tandem Computers Incorporated
Automatic Fault Tolerance
Working with the GUARDIAN 90 operating system, PATHWAY automatically
ensures that applications remain continually available to their end users—you need
not write the code that supports this availability. For example, PATHWAY allows
both TCPs and server processes to run as NonStop process pairs. In such pairs, a
primary process runs in one CPU and a backup process in another CPU. The
operating system automatically manages the sending of checkpoint messages from the
primary to the backup process so that the backup process can continue running the
application if the primary process fails. In addition, the entire database can be
protected by TMF.
Application Development Tools
With PATHWAY, you receive three valuable application development tools: the
SCREEN COBOL compiler, the PATHAID interactive screen builder, and the SCREEN
COBOL Utility Program (SCUP). These tools, and other tools and features that will be
explained later, are illustrated in Figure 6-2.
The SCREEN COBOL compiler processes the procedural language used to
develop your screen programs. This language is similar to standard COBOL, but
contains additional features for displaying and manipulating data on user
terminals and other devices. SCREEN COBOL allows you to write statements that
display forms containing transaction data to the end user, accept data from the end
user, send data and processing instructions to a server, and call other screen
programs. Because one screen program can call another, you can use SCREEN
COBOL to develop a hierarchy of simple programs to perform different
application functions. For example, a set of programs for an order-entry
application might include a logon screen, a menu screen, several order screens,
and help screens.
PATHAID is a screen builder program that simplifies the job of designing the
forms that your screen program displays on the end user’s terminal. With
PATHAID, you can paint screens directly on your own terminal, specify formats
for the screen fields, and assign display attributes to those fields. Then, you can
generate SCREEN COBOL source code for screen descriptions, based on those
screen picture layouts and attributes. You can edit the screen descriptions, copy
them directly into your screen programs, or store them in screen library files.