<s>
The	O
Unisys	O
Data	O
Management	O
System	O
II	O
(	O
DMSII	O
)	O
is	O
a	O
database	B-Application
system	I-Application
originally	O
created	O
by	O
the	O
Burroughs	O
Corporation	O
in	O
1972	O
.	O
</s>
<s>
The	O
later	O
,	O
A	O
Series	O
,	O
Clearpath	O
,	O
Libra	O
product	O
lines	O
support	O
it	O
and	O
in	O
recent	O
releases	O
of	O
Unisys	B-Device
Clearpath	I-Device
software	O
it	O
has	O
been	O
renamed	O
as	O
the	O
Enterprise	O
Database	O
Server	O
for	O
ClearPath	O
MCP	O
.	O
</s>
<s>
It	O
originally	O
competed	O
with	O
IBM	O
's	O
IMS	B-Application
and	O
CICS	B-Application
products	O
and	O
predated	O
the	O
popularity	O
of	O
relational	O
databases	B-Application
.	O
</s>
<s>
DMSII	O
provided	O
an	O
ISAM	B-Application
(	O
indexed	B-Application
sequential	I-Application
access	I-Application
method	I-Application
)	O
model	O
for	O
data	O
access	O
,	O
transaction	O
isolation	O
and	O
database-recovery	O
capabilities	O
.	O
</s>
<s>
The	O
database	B-Application
schema	I-Application
was	O
written	O
in	O
the	O
proprietary	O
Data	O
and	O
Structure	O
Definition	O
Language	O
(	O
DASDL	O
)	O
.	O
</s>
<s>
Proprietary	O
language	O
compilers	O
(	O
such	O
as	O
COBOL	B-Application
and	O
ALGOL	B-Language
)	O
would	O
use	O
the	O
database	O
description	O
file	O
to	O
create	O
database-related	O
elements	O
in	O
the	O
object	O
code	O
of	O
the	O
compiled	O
program	O
.	O
</s>
<s>
The	O
source	O
for	O
the	O
data	O
structures	O
was	O
maintained	O
in	O
an	O
ordinary	O
CANDE	B-Operating_System
source	O
file	O
.	O
</s>
<s>
The	O
application	O
programmer	O
merely	O
needed	O
to	O
re-compile	O
his	O
application	O
source	O
(	O
typically	O
COBOL	B-Application
)	O
against	O
the	O
new	O
description	O
file	O
and	O
the	O
programmer	O
could	O
take	O
advantage	O
of	O
new	O
data	O
elements	O
in	O
the	O
structures	O
.	O
</s>
<s>
Index	O
sets	O
included	O
ISAM	B-Application
styles	O
(	O
which	O
used	O
field	O
keys	O
to	O
reference	O
records	O
)	O
and	O
bit-vectored	O
sets	O
(	O
which	O
used	O
Boolean	O
representation	O
of	O
set	O
membership	O
if	O
the	O
data	O
set	O
record	O
met	O
conditions	O
defined	O
in	O
the	O
set	O
)	O
.	O
</s>
<s>
Like	O
ISAM	B-Application
,	O
it	O
used	O
sets	O
(	O
indexes	O
where	O
all	O
records	O
were	O
referenced	O
,	O
such	O
as	O
the	O
index	O
in	O
Microsoft	B-Application
Access	I-Application
)	O
,	O
subsets	O
(	O
a	O
partial	O
list	O
of	O
records	O
dependent	O
upon	O
a	O
definable	O
condition	O
,	O
e.g.	O
</s>
<s>
There	O
is	O
a	O
substantial	O
difference	O
between	O
DMSII	O
and	O
relational	O
databases	B-Application
:	O
in	O
DMSII	O
,	O
a	O
record	O
can	O
only	O
be	O
retrieved	O
via	O
an	O
index	O
if	O
the	O
index	O
was	O
designed	O
initially	O
(	O
or	O
after	O
a	O
reorganization	O
which	O
generates	O
a	O
new	O
subset	O
from	O
all	O
the	O
data	O
in	O
the	O
set	O
)	O
.	O
</s>
<s>
That	O
layer	O
was	O
programmed	O
in	O
Pascal	B-Application
and	O
followed	O
the	O
runtime-selection	O
approach	O
,	O
as	O
the	O
relational	O
model	O
does	O
.	O
</s>
