Pathway/iTS SCREEN COBOL Reference Manual (G06.24+, H06.03+, Pathway/iTS 1.0+)

Introduction to SCREEN COBOL
Compaq NonStop™ Pathway/iTS SCREEN COBOL Reference Manual—426750-001
1-6
Pathway System Components
A server is configured to be a member of a particular server class. The server class itself
has specific characteristics that are defined within the PATHMON configuration.
Individual servers within a server class use copies of the same server program code and
separate data areas; the PATHMON process creates new servers from a single server
program according to the configuration instructions.
A SCREEN COBOL program and its associated servers require corresponding message
descriptions. To ensure message description correspondence, both programs can use
common code for the description obtained from a source code library.
Figure 1-3
illustrates the message description correspondence between a SCREEN
COBOL requester and a COBOL server.
Transaction Management Facility (TMF)
TMF maintains the consistency of a database and provides the tools for database
recovery. TMF requires that monitored data files be flagged for auditing. TMF audits a
file by maintaining before and after images of changes to the files. These images
provide the basis for transaction backout, which cancels the effects of a partially
completed transaction, and database rollforward, which restores a database to a
consistent state after a catastrophic failure.
SCREEN COBOL programs communicate with TMF by executing particular
statements. The BEGIN-TRANSACTION statement marks the beginning of a
transaction, when the terminal enters transaction mode. The terminal remains in
transaction mode until execution of the SCREEN COBOL END-TRANSACTION (or
ABORT-TRANSACTION) statement. These statements begin and end a sequence of
operations that are treated as a single transaction by TMF.
An executing SCREEN COBOL program is called a terminal-program unit in
Pathway/iTS. To communicate with TMF, the terminal-program unit must be
configured for TMF by issuing commands to PATHCOM.
Figure 1-3. Message Description Correspondence
003CDT .CDD
Data Descriptions
COBLIB
MESSAGE-IN
IDENTIFICATION DIVISION.
.
.
.
DATA DIVISION.
WORKING-STORAGE SECTION.
COPY MESSAGE-IN OF COBLIB
.
.
.
IDENTIFICATION DIVISION.
.
.
.
DATA DIVISION.
FILE SECTION.
FD F-MESSAGE-IN
LABEL RECORDS ARE OMITTED.
COPY MESSAGE-IN OF COBLIB.
.
.
.
SCREEN COBOL Source Code COBOL Server Source Code
CDT 003.CDD