<s>
The	O
IBM	B-Application
Information	I-Application
Management	I-Application
System	I-Application
(	O
IMS	O
)	O
is	O
a	O
joint	O
hierarchical	B-General_Concept
database	I-General_Concept
and	O
information	B-Application
management	I-Application
system	I-Application
that	O
supports	O
transaction	B-General_Concept
processing	I-General_Concept
.	O
</s>
<s>
In	O
the	O
interim	O
period	O
,	O
IMS	O
has	O
undergone	O
many	O
developments	O
as	O
IBM	B-Application
System/360	I-Application
technology	O
evolved	O
into	O
the	O
current	O
z/OS	B-Application
and	O
IBM	B-Device
zEnterprise	I-Device
System	O
technologies	O
.	O
</s>
<s>
For	O
example	O
,	O
IMS	O
now	O
supports	O
the	O
Java	B-Language
programming	I-Language
language	I-Language
,	O
JDBC	B-Language
,	O
XML	B-Protocol
,	O
and	O
,	O
since	O
late	O
2005	O
,	O
web	O
services	O
.	O
</s>
<s>
Vern	B-Application
Watts	I-Application
was	O
IMS	O
's	O
chief	O
architect	O
for	O
many	O
years	O
.	O
</s>
<s>
The	O
IMS	O
Database	O
component	O
stores	O
data	O
using	O
a	O
hierarchical	B-General_Concept
model	I-General_Concept
,	O
which	O
is	O
quite	O
different	O
from	O
IBM	O
's	O
later	O
released	O
relational	B-Application
database	I-Application
,	O
IBM	B-Application
Db2	I-Application
.	O
</s>
<s>
In	O
IMS	O
,	O
the	O
hierarchical	B-General_Concept
model	I-General_Concept
is	O
implemented	O
using	O
blocks	O
of	O
data	O
known	O
as	O
segments	O
.	O
</s>
<s>
In	O
practice	O
,	O
often	O
all	O
data	O
in	O
a	O
segment	O
may	O
map	O
to	O
a	O
COBOL	B-Application
copybook	O
.	O
</s>
<s>
Besides	O
DL/I	B-Language
query	O
usage	O
,	O
a	O
field	O
may	O
be	O
defined	O
in	O
IMS	O
so	O
that	O
the	O
data	O
can	O
be	O
hidden	O
from	O
certain	O
applications	O
for	O
security	O
reasons	O
.	O
</s>
<s>
The	O
database	O
component	O
of	O
IMS	O
can	O
be	O
purchased	O
standalone	O
,	O
without	O
the	O
transaction	B-General_Concept
manager	I-General_Concept
component	O
,	O
and	O
used	O
by	O
systems	O
such	O
as	O
CICS	B-Application
.	O
</s>
<s>
There	O
are	O
three	O
basic	O
forms	O
of	O
IMS	O
hierarchical	B-General_Concept
databases	I-General_Concept
:	O
</s>
<s>
Directly	O
descended	O
from	O
the	O
Data	B-Language
Language	I-Language
Interface	I-Language
(	O
DL/I	B-Language
)	O
databases	O
originally	O
developed	O
for	O
Apollo	O
,	O
full	O
function	O
databases	O
can	O
have	O
primary	O
and	O
secondary	O
indexes	O
,	O
accessed	O
using	O
DL/I	B-Language
calls	O
from	O
an	O
application	O
program	O
,	O
like	O
SQL	B-Language
calls	O
to	O
IBM	B-Application
Db2	I-Application
or	O
Oracle	B-General_Concept
.	O
</s>
<s>
Full	O
function	O
databases	O
store	O
data	O
using	O
VSAM	O
,	O
a	O
native	O
z/OS	B-Application
access	O
method	O
,	O
or	O
Overflow	O
Sequential	O
(	O
OSAM	O
)	O
,	O
an	O
IMS-specific	O
access	O
method	O
that	O
optimizes	O
the	O
I/O	O
channel	O
program	O
for	O
IMS	O
access	O
patterns	O
.	O
</s>
<s>
Starting	O
with	O
IMS	O
Version	O
11	O
,	O
DEDBs	O
can	O
use	O
z/OS	B-Application
64-bit	O
storage	O
for	O
database	O
buffers	O
.	O
</s>
<s>
DL/I	B-Language
databases	O
can	O
be	O
built	O
atop	O
either	O
VSAM	O
or	O
OSAM	O
,	O
with	O
some	O
restrictions	O
depending	O
on	O
database	O
organization	O
.	O
</s>
<s>
Although	O
the	O
maximum	O
size	O
of	O
a	O
z/OS	B-Application
VSAM	O
dataset	O
increased	O
to	O
128TB	O
a	O
few	O
years	O
ago	O
,	O
IMS	O
still	O
limits	O
a	O
VSAM	O
dataset	O
to	O
4GB	O
(	O
and	O
OSAM	O
to	O
8GB	O
)	O
.	O
</s>
<s>
IMS	O
,	O
with	O
assistance	O
from	O
z/OS	B-Application
hardware	O
the	O
Coupling	O
Facility	O
supports	O
N-way	O
inter-IMS	O
sharing	O
of	O
databases	O
.	O
</s>
<s>
Many	O
large	O
configurations	O
involve	O
multiple	O
IMS	B-Application
systems	I-Application
managing	O
common	O
databases	O
,	O
a	O
technique	O
providing	O
for	O
scalable	O
growth	O
and	O
system	O
redundancy	O
in	O
the	O
event	O
of	O
hardware	O
or	O
software	O
failures	O
.	O
</s>
<s>
IMS	O
is	O
also	O
a	O
robust	O
transaction	B-General_Concept
manager	I-General_Concept
(	O
IMS	O
TM	O
,	O
also	O
known	O
as	O
IMS	O
DC	O
)	O
one	O
of	O
the	O
"	O
big	O
three	O
"	O
classic	O
transaction	B-General_Concept
managers	I-General_Concept
along	O
with	O
CICS	B-Application
and	O
BEA	O
(	O
now	O
Oracle	B-General_Concept
)	O
Tuxedo	B-Application
.	O
</s>
<s>
A	O
transaction	B-General_Concept
manager	I-General_Concept
interacts	O
with	O
an	O
end	O
user	O
(	O
connected	O
through	O
VTAM	B-Application
or	O
TCP/IP	B-Protocol
,	O
including	O
3270	B-Operating_System
and	O
Web	O
user	O
interfaces	O
)	O
or	O
another	O
application	O
,	O
processes	O
a	O
business	O
function	O
(	O
such	O
as	O
a	O
banking	O
account	O
withdrawal	O
)	O
,	O
and	O
maintains	O
state	O
throughout	O
the	O
process	O
,	O
making	O
sure	O
that	O
the	O
system	O
records	O
the	O
business	O
function	O
correctly	O
to	O
a	O
data	O
store	O
.	O
</s>
<s>
Thus	O
IMS	O
TM	O
is	O
quite	O
like	O
a	O
Web	O
application	O
,	O
operating	O
through	O
a	O
CGI	B-Language
program	I-Language
(	O
for	O
example	O
)	O
,	O
to	O
provide	O
an	O
interface	O
to	O
query	O
or	O
update	O
a	O
database	O
.	O
</s>
<s>
IMS	O
TM	O
typically	O
uses	O
either	O
IMS	O
DB	O
or	O
Db2	B-Application
as	O
its	O
backend	O
database	O
.	O
</s>
<s>
When	O
used	O
alone	O
with	O
Db2	B-Application
the	O
IMS	O
TM	O
component	O
can	O
be	O
purchased	O
without	O
the	O
IMS	O
DB	O
component	O
.	O
</s>
<s>
An	O
IMS	O
control	O
program	O
receives	O
a	O
transaction	O
entered	O
from	O
a	O
terminal	O
(	O
or	O
Web	O
browser	O
or	O
other	O
application	O
)	O
and	O
then	O
stores	O
the	O
transaction	O
on	O
a	O
message	B-Operating_System
queue	I-Operating_System
(	O
in	O
memory	O
or	O
in	O
a	O
dataset	O
)	O
.	O
</s>
<s>
The	O
message	O
processing	O
region	O
retrieves	O
the	O
transaction	O
from	O
the	O
IMS	O
message	B-Operating_System
queue	I-Operating_System
and	O
processes	O
it	O
,	O
reading	O
and	O
updating	O
IMS	O
and/or	O
Db2	B-Application
databases	I-Application
,	O
assuring	O
proper	O
recording	O
of	O
the	O
transaction	O
.	O
</s>
<s>
Then	O
,	O
if	O
required	O
,	O
IMS	O
enqueues	O
a	O
response	O
message	O
back	O
onto	O
the	O
IMS	O
message	B-Operating_System
queue	I-Operating_System
.	O
</s>
<s>
In	O
2013	O
IBM	O
completed	O
a	O
benchmark	O
on	O
IMS	O
Version	O
13	O
demonstrating	O
the	O
ability	O
to	O
process	O
100,000	O
transactions	O
per	O
second	O
on	O
a	O
single	O
IMS	B-Application
system	I-Application
.	O
</s>
<s>
Prior	O
to	O
IMS	O
,	O
businesses	O
and	O
governments	O
had	O
to	O
write	O
their	O
own	O
transaction	B-General_Concept
processing	I-General_Concept
environments	O
.	O
</s>
<s>
Today	O
IMS	O
complements	O
IBM	B-Application
Db2	I-Application
,	O
IBM	O
's	O
relational	B-Application
database	I-Application
system	O
,	O
introduced	O
in	O
1982	O
.	O
</s>
<s>
In	O
general	O
,	O
IMS	O
performs	O
faster	O
than	O
Db2	B-Application
for	O
the	O
common	O
tasks	O
but	O
may	O
require	O
more	O
programming	O
effort	O
to	O
design	O
and	O
maintain	O
for	O
non-primary	O
duties	O
.	O
</s>
<s>
Relational	B-Application
databases	I-Application
have	O
generally	O
proven	O
superior	O
in	O
cases	O
where	O
the	O
requirements	O
,	O
especially	O
reporting	O
requirements	O
,	O
change	O
frequently	O
or	O
require	O
a	O
variety	O
of	O
viewpoint	O
"	O
angles	O
"	O
outside	O
the	O
primary	O
or	O
original	O
function	O
.	O
</s>
