Introduction to TRANSFER Delivery System

The TRANSFER Delivery System GUARDIAN 90 and EXPAND—Distributed
Processing
Introduction to TRANSFER Delivery System—109426 1-11
GUARDIAN 90 software provides both a file structure and a file-access definition. An
access method is an I/O process that controls a device. TRANSFER applications use
two kinds of access methods:
■ Disk access methods
This software gives programmers flexibility in determining the layout of files and
gives applications access to the files. The files that make up a database, or even a
single file, can be distributed throughout a network.
■ Data communications access methods
These processes give applications control over many kinds of terminals and data
communications lines. An application does not need to know the protocols for data
communications; the application uses strings of characters and lets the access
method handle the protocol.
Figure 1-4. Interprocess Communication
Issue Request
Request Outstanding—
Do This Update
Return Data
Process A gathers data in the form
of a request from the terminal and
delivers the request to Process B.
Process A is the requester. Process
B receives the request and, acting as
the server, examines the contents
and decides to request calls for an
update to the database.
Process B issues a request to
Process C, the GUARDIAN 90 disk
process; now Process B is the
requester.
Process C updates the database
and then replies to Process B.
Process B replies to Process A.
A
(Server)
A
(Requester)
C
ABC
Return Data
AB
S8123-004
B
B