Introduction to TRANSFER Delivery System

The TRANSFER Delivery System PATHWAY—Online Transaction Processing
Introduction to TRANSFER Delivery System—109426 1-13
PATHWAY—Online Transaction Processing
PATHWAY is both an operating environment and a development tool for online
transaction processing applications. In the PATHWAY environment, applications are
divided into requesters and servers. PATHWAY establishes the framework for creating
requesters and servers and then manages them. PATHWAY ensures that servers and
requesters are both fault-tolerant and expandable, and it enables applications to be
distributed.
Requesters are the parts of an application that deal with the terminal, doing such tasks as
displaying screens (requester code implements your menus and screens), accepting data,
and requesting the appropriate function from the server.
Servers are the parts of an application that deal with the database itself, handling all
tasks related to the application computations and database access. Servers are processes
written in COBOL, FORTRAN, Pascal, C, or TAL, the Tandem Transaction
Application Language.
When a server examines or modifies a database in response to a request, the protocol is
as follows:
■ A SEND statement in a SCREEN COBOL program unit results in a request to a
server on behalf of the terminal controlled by that program unit. The requester and
server can run in different processors or on different nodes in the network. Usually,
the requester runs on the node where the terminal is defined, and the server is on the
node where the data resides.
■ The server receives the request, processes it, and returns a response as an
acknowledgment. Because the database access or update must be completed by the
time the server replies, the transaction occurs online.
Figure 1-6 illustrates the requester-server model. At the center of the figure is the
application; it contains three requesters and three servers. On the left, you see a
representation of the requester code, and on the right, a representation of the server code.