Using Externally Described Disk Files

Using Externally Described Disk Files

Externally described DISK files are identified by an E in position 22 description specifications. The E indicates that the compiler is to re external description of the file from the system when the program is Therefore, you must create the file before the program is compiled.

The external description for a DISK file includes:

¹The record-format specifications that contain a description of the record

¹Access path specifications that describe how the records are to

These specifications result from the DDS for the file and the OS/400 command that is used for the file.

Record Format Specifications

The record-format specifications allow you to describe the fields in location of the fields in a record. The fields are located in the specified in the DDS. The field description generally includes the fi field type, and the field length (including the number of decimal pos numeric field). Instead of specifying the field attributes in the re physical or logical file, you can define them in a field-reference f

In

addition,

the DDS keywords

can

be

used

to:

 

 

 

 

 

¹

Specify

that

duplicate key

values are

not

allowed for the file (U

¹

Specify

a

text

description

for

a

record

format

or

a

field

(TEXT).

For

a complete

list

of

the

DDS

keywords

that

are

valid

for

a

databa

DB2 UDB for AS/400 Database Programming.

 

 

 

 

 

 

 

 

Figure 139

on

page 283

shows

an

example

of the DDS

for

a

database f

Figure 140

on

page 284

for a field-reference

file that defines the a

fields used in the databaseDDS fileR .ferSenceforthe

more information

on

a

field-reference

file.

 

 

 

 

 

 

 

 

 

 

 

 

Access Path

The description of an externally described file contains the access p describes how records are to be retrieved from the file. Records based on an arrival sequence (non-keyed) access path or on a keyed-se access path.

The arrival sequence access path is based on the order in which the stored in the file. Records are added to the file one after anoth

For

the

keyed-sequence access path, the sequence of records

in the

on

the

contents

of

the

key

field that is defined in the DDS

for

th

in

the

DDS shown

in

Figure 139 on

page 283, CUST is defined as

the

key

The

keyed-sequence

access

path

is updated whenever records are

add

or

when

the contents of

a

key

field change.

 

 

For a complete description of the access paths for an externally des base file, seeDB2 theUDB for AS/400 Database Programmingmanual.

282 ILE RPG for AS/400 Programmer's Guide

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IBM AS/400 manual Using Externally Described Disk Files, Record Format Specifications, Access Path
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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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