Defining Externally Described Files

.2/

An externally described file (that is, a file with field-lev

 

description) is used as a program-described file

in

the

pro

 

program-described file is identified by an F in position 22

 

description specifications. This entry tells the compiler not

 

external field-level descriptions. This file

does

not

have

to

 

lation

time.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

.3/

A file is described only at the record

level

to

the

opera

 

fields

in

the

record

are

described

within

the program;

the

 

22

of

the

file description

specifications

must

contain

an F.

 

not

have

to

exist

at

compilation

time.

 

 

 

 

 

 

 

 

.4/

A file

name

can be specified at compilation

time

(that

is,

 

RPG

source

member),

and

a

different

file

name

can

be

speci

 

time. The

E

in

position

22

of

the

file

description

specifica

 

that

the

external

description

of

the

file

is

to

be

copied

 

time. At run time, a file override command

can

be

used

so

 

ferent

file

is accessed by the program.

To

override

a

fil

 

must

make

sure

that

record

names

in

both

files

are

the

same

 

program

uses

the record-format name on the

input/output

operat

 

such as a READ operation where it specifies what record t

 

expected. See “Overriding and Redirecting

File

Input

and

Out

 

page 273

for

more

information.

 

 

 

 

 

 

 

 

 

 

 

 

Defining Externally Described

Files

You

can

use DDS to describe files to the OS/400 system. Each recor

file

is

identified by a unique record-format name.

An E entry in position 22 of the file description specifications i externally described file. The E entry indicates to the compiler th the external description of the file from the system when the prog

The information in this external description includes:

¹ File

information, such

as file

type,

and file attributes, such as

(by

key or relative

record

number)

 

¹Record-format description, which includes the record format name a descriptions (names, locations, and attributes).

The

information

the

compiler

retrieves from

the external description i

the compiler listing as long

as OPTION(*EXPDDS)

is

specified on either

CRTRPGMOD or CRTBNDRPG

command

when compiling the source member.

(The

default

for

both of

these commands

is

OPTION(*EXPDDS).)

The following section describes how to use a file description speci rename or ignore record formats and how to use input and output spe modify external descriptions. Remember that input and output specific externally described files are optional.

Chapter 14. Defining Files265

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IBM AS/400 manual Defining Externally Described Files, Option*Expdds
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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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