<s>
An	O
indexed	B-Language
file	I-Language
is	O
a	O
computer	B-Operating_System
file	I-Operating_System
with	O
an	O
index	B-Data_Structure
that	O
allows	O
easy	O
random	B-General_Concept
access	I-General_Concept
to	O
any	O
record	B-General_Concept
given	O
its	O
file	O
key	B-Application
.	O
</s>
<s>
The	O
key	B-Application
must	O
be	O
such	O
that	O
it	O
uniquely	O
identifies	O
a	O
record	B-General_Concept
.	O
</s>
<s>
If	O
more	O
than	O
one	O
index	B-Data_Structure
is	O
present	O
the	O
other	O
ones	O
are	O
called	O
alternate	O
indexes	O
.	O
</s>
<s>
IBM	O
supports	O
indexed	B-Language
files	I-Language
with	O
the	O
Indexed	B-Application
Sequential	I-Application
Access	I-Application
Method	I-Application
(	O
ISAM	B-Application
)	O
on	O
OS/360	B-Application
and	I-Application
successors	I-Application
.	O
</s>
<s>
IBM	O
virtual	B-Application
storage	I-Application
operating	I-Application
systems	I-Application
added	O
VSAM	O
,	O
which	O
supports	O
indexed	B-Language
files	I-Language
as	O
Key	B-Application
Sequenced	I-Application
Data	I-Application
Sets	I-Application
(	O
KSDS	O
)	O
,	O
with	O
more	O
options	O
.	O
</s>
<s>
Support	O
for	O
indexed	B-Language
files	I-Language
is	O
built	O
into	O
COBOL	B-Application
and	O
PL/I	B-Language
.	O
</s>
<s>
Other	O
languages	O
with	O
more	O
limited	O
I/O	O
facilities	O
such	O
as	O
C	B-Language
support	O
indexed	B-Language
files	I-Language
through	O
add-on	O
packages	O
in	O
a	O
runtime	O
library	O
such	O
as	O
C-ISAM	O
.	O
</s>
<s>
Some	O
of	O
Digital	O
's	O
operating	O
systems	O
,	O
such	O
as	O
OpenVMS	B-Operating_System
,	O
support	O
indexed	B-Language
file	I-Language
I/O	O
using	O
the	O
Record	B-Application
Management	I-Application
Services	I-Application
.	O
</s>
<s>
In	O
recent	O
systems	O
,	O
relational	B-Application
databases	I-Application
are	O
often	O
used	O
in	O
place	O
of	O
indexed	B-Language
files	I-Language
.	O
</s>
<s>
IBM	O
PL/I	B-Language
uses	O
the	O
file	O
attribute	O
ENVIRONMENT(INDEXED )	O
or	O
ENVIRONMENT(VSAM )	O
to	O
declare	O
an	O
indexed	B-Language
file	I-Language
.	O
</s>
