Types of File Descriptions

¹Less maintenance activity when the file’s record format is changed. often update programs by changing the file’s record format and the piling the programs that use the files without changing any coding i program.

¹Improved documentation because programs using the same files use co

record-format and field names.

¹ Improved reliability.

If

level checking is specified, the RPG progr

the

user

if there

are

changes in the external description. See “L

on

page 270

for further

information.

If an externally described file (identified by an E in position 22 specification) is specified for the devices SEQ or SPECIAL, the RPG pro the field descriptions for the file, but the interface to the oper though the file were a program-described file. Externally described f specify device-dependent functions such as forms control for PRINTER fil because this information is already defined in the external descripti

Using Files with

External-Description

as

Program-Described

 

 

 

A

file created

from

external descriptions can

be

used

as a program-d

the program. To use

an externally described

file

as a

program-describ

1.Specify the file as program-described (F in position 22) in the f specification of the program.

2. Describe the fields in the records on the input or/and output sp the program.

At compile time, the compiler uses the field descriptions in the input specifications. It does not retrieve the external descriptions.

Example of Some Typical Relationships between

OS/400

Field-Level

Description of

a File

Programs and

OS/400

Record-Level

Description of

a File

Files

OS/400

Field-Level

Description of

a File

1RPG

Externally Described File (E in position 22)

2RPG

Program-Described File (F in position

22)- The compiler does not copy in field-level description

3RPG

Program-Described File (F in position 22)

4RPG

Externally Described File (E in position 22)

Figure 129. Typical Relationships between an RPG Program and Files on the AS/400 System

 

.1/

The program uses

the field-level description

of a file that is

 

the operating system. An externally described file is identifi

 

position 22 of the file description specifications. At compilat

 

compiler copies in

the external field-level

description.

264 ILE RPG for AS/400 Programmer's Guide

Page 287 Page 289
Page 288
Image 288
IBM AS/400 manual Using Files with, Program-Described, Example of Some Typical Relationships between, Programs
Page 287 Page 289

AS/400 specifications

The IBM AS/400, now known as the IBM iSeries, is a midrange computer system that has been a cornerstone of enterprise computing since its introduction in 1988. Designed to provide a robust platform for business applications, the AS/400 is celebrated for its reliability, scalability, and integrated database capabilities.

One of the key features of the AS/400 is its Integrated Operating Environment, which blends hardware and software resources seamlessly. This integration allows businesses to execute diverse workloads, ranging from traditional applications to modern web-based services, all on a single platform. The operating system, OS/400 (now IBM i), offers a rich set of APIs and tools for developers, simplifying application development and management.

Another standout characteristic of the AS/400 is its built-in database, DB2 for i. This powerful relational database management system allows for efficient data handling and provides advanced features such as support for SQL, XML, and JSON, making it easier for businesses to manage their data and integrate it with other systems. The database's tight integration with the operating system enables high performance and security.

In terms of scalability, the AS/400 can accommodate small businesses as well as large enterprises, with the ability to support hundreds of users simultaneously. Its architecture allows for easy upgrades in hardware, meaning that organizations can scale their systems without replacing the entire infrastructure.

Security is another critical attribute of the AS/400. With a sophisticated security model, it offers built-in user authentication, access control, encryption, and auditing capabilities to protect data and applications from unauthorized access.

The AS/400 also supports multiple programming languages, including RPG, COBOL, Java, and PHP, giving organizations the flexibility to choose the development tools that best fit their needs. This diversity helps maintain legacy applications while also developing new ones that leverage modern technologies.

Moreover, the platform supports both traditional green-screen interfaces and modern graphical user interfaces, allowing organizations to transition smoothly into contemporary user experience paradigms.

Overall, the IBM AS/400 stands out as a resilient, flexible, and secure computing platform that enables organizations to effectively manage their business operations, streamline processes, and adapt to changing market demands. Its unique combination of integrated features and capabilities ensures that it remains relevant in today's fast-paced technology landscape.
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