Pathmaker Programming Guide

Designing a Pathmaker Application
Preparing for Pathmaker Application Development
067868 Tandem Computers Incorporated 2–5
Designing Custom Services A service is a unit of work to be performed by a server. A service corresponds to the
work performed by a function key action. The Pathmaker product offers three types of
services:
Standard services
Registered services
Custom services
Standard services, the services provided by the Pathmaker product, include reading
the next record or inserting a new record. Standard services can be invoked only by
DB requesters. You do not design standard services.
Application developers create registered services as part of registering a server not
created with the Pathmaker product. You do not design registered services. Refer to
Section 4 for more information about registered services and servers.
Custom services, the services application developers write, can be designed to perform
more complex operations like inserting an airline flight reservation record or
transferring money from one bank account record to another. Custom service code is
written in either COBOL85 or C. Custom services are invoked by transaction (TRNS)
requesters. Each custom service must be designed and written as a context-free
process. (For further information about context-free services, consult the Introduction
to Pathmaker manual.)
A single custom service can access both NonStop SQL databases and Enscribe files. If
a custom service accesses a NonStop SQL table, the application developer includes
embedded NonStop SQL code in the service. Application developers can use the
Pathmaker product to produce some NonStop SQL data manipulation statements for
custom services written in COBOL85. (See “Deciding Whether to Modify Files Used
for Code Generation” later in this section.)
If your application design requires the database to be audited using the Transaction
Monitoring Facility (TMF), application developers must indicate that TMF is to be
used for every custom service they create for the application. The service itself is not
audited.
Before you can design custom services for a Pathmaker application, you must be
familiar with the structure of a Pathmaker custom service and must know which
portions of custom services and servers the Pathmaker product provides and which
portions are created by applications developers. Refer to Section 4 of this manual for
information about these topics.
Designing Custom Servers
and Server Classes
A server is an application module that receives processing requests from a requester.
A server manages the database by receiving requests from the requester and invoking
services to add, modify, or delete data and perform calculations. Pathmaker servers
open and close files and communicate with requesters. Services are logical modules
within the server that do database I/O and computation.
Each server process handles one request completely before going on to the next. The
Pathmaker product offers three types of servers: