IBM AS/400 Accessing, Database Files, Physical Files and Logical Files, Data Files and Source

Database Files

Chapter 16. Accessing

Database

Files

You

can

access

a

database

file

from

your program by associating t

with

the

device

DISK

in

the appropriate

file

specification.

DISK

files

of

an

ILE

RPG program

also

associate

with distributed

da

(DDM)

files,

which

allow

you

to access

files on

remote

systems as

d

Database Files

Database

files

are objects

of

type

*FILE

on

the

AS/400. They can be e

ical or logical files and either externally described

or program-des

access database

files

by

associating

the file name with the devic

36 through

42

of

the

file

description

specifications.

Database files can be created by OS/400 Create File commands. For m mation on describing and creating database DB2files,UDBreferfo toAS/400the Database Programming manual and theDDS Reference.

Physical Files and Logical Files

Physical files contain the actual data that is stored on the system, a description of how data is to be presented to or received from a contain only one record format, and one or more members. Records in files can be externally or program-described.

A physical file can have a keyed sequence access path. This means presented to a program in a sequence based on one or more key fi

Logical

files

do not contain data. They

contain a

description

of

record

one

or

more

physical

files. A

logical

file

is

a

view or

representat

physical

files.

Logical

files

that

contain

more

than

one

format

are

r

multi-format

logical files.

If your program processes a

logical

file

which

contains

more

than

on

format,

you

can

use

a

read

by

record format

to

set

the format

y

Data Files and Source

Files

A data

file

contains

actual

data,

or a view of the

data.

Records

in

grouped

into

members.

All

the

records

in

a

file

can be

in

one

membe

be grouped into different members. Most database commands and opera

default

assume that database

files

which onlycontainone memberdata.haveThis

means that when your program accesses

database

files

containing

data

need

to specify

the

member

name for

the file

unless

your

file

con

one

member.

If

your

file contains

more

than

one

member

and

a partic

is not

specified, the

first

member

is

used.

Usually, database files that contain source programs are made up of member. Organizing source programs into members within database files

you to better manage your programssource member. The contains source state- ments that the system uses to create program objects.

 Copyright IBM Corp. 1994, 1999 281