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

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