<s>
An	O
enterprise	B-Application
messaging	I-Application
system	I-Application
(	O
EMS	O
)	O
or	O
messaging	O
system	O
in	O
brief	O
is	O
a	O
set	O
of	O
published	O
enterprise-wide	O
standards	O
that	O
allows	O
organizations	O
to	O
send	O
semantically	O
precise	O
messages	O
between	O
computer	O
systems	O
.	O
</s>
<s>
EMS	O
systems	O
promote	O
loosely	B-Application
coupled	I-Application
architectures	O
that	O
allow	O
changes	O
in	O
the	O
formats	O
of	O
messages	O
to	O
have	O
minimum	O
impact	O
on	O
message	O
subscribers	O
.	O
</s>
<s>
EMS	O
systems	O
are	O
facilitated	O
by	O
the	O
use	O
of	O
structured	O
messages	O
(	O
such	O
as	O
using	O
XML	B-Protocol
or	O
JSON	B-General_Concept
)	O
,	O
and	O
appropriate	O
protocols	O
,	O
such	O
as	O
DDS	B-Application
,	O
MSMQ	B-Application
,	O
AMQP	B-Operating_System
or	O
SOAP	B-Protocol
with	O
web	O
services	O
.	O
</s>
<s>
Policy	O
:	O
Enterprise	B-Application
messaging	I-Application
systems	I-Application
should	O
provide	O
some	O
consideration	O
for	O
a	O
centralized	O
policy	O
of	O
messages	O
such	O
as	O
what	O
classes	O
or	O
roles	O
of	O
users	O
can	O
access	O
different	O
fields	O
of	O
any	O
message	O
.	O
</s>
<s>
Message	O
body	O
semantics	B-Application
Message	O
body	O
semantics	B-Application
include	O
the	O
precise	O
definition	O
of	O
all	O
of	O
the	O
data	O
elements	O
in	O
the	O
body	O
of	O
the	O
message	O
.	O
</s>
<s>
Message	O
semantics	B-Application
can	O
be	O
aided	O
by	O
the	O
use	O
of	O
a	O
precise	O
data	O
dictionary	O
that	O
documents	O
metadata	O
.	O
</s>
<s>
The	O
commonalities	O
between	O
messaging	O
systems	O
(	O
in	O
terms	O
of	O
capabilities	O
and	O
architecture	O
)	O
have	O
been	O
captured	O
in	O
a	O
platform-independent	O
fashion	O
as	O
enterprise	B-Application
integration	I-Application
patterns	I-Application
(	O
a.k.a.	O
</s>
<s>
Although	O
similar	O
in	O
concept	O
to	O
an	O
enterprise	B-Application
service	I-Application
bus	I-Application
(	O
ESB	O
)	O
,	O
an	O
EMS	O
places	O
emphasis	O
on	O
design	O
of	O
messaging	O
protocols	O
(	O
for	O
instance	O
,	O
using	O
DDS	B-Application
,	O
MSMQ	B-Application
or	O
AMQP	B-Operating_System
)	O
,	O
not	O
the	O
implementation	O
of	O
the	O
services	O
using	O
a	O
specific	O
technology	O
such	O
as	O
web	O
services	O
,	O
DDS	B-Application
APIs	B-Application
for	O
C/C	O
++	O
and	O
Java	O
,	O
.NET	B-Application
or	O
Java	B-Language
Message	I-Language
Service	I-Language
(	O
JMS	O
)	O
.	O
</s>
<s>
Note	O
that	O
an	O
Enterprise	B-Application
Messaging	I-Application
System	I-Application
should	O
not	O
be	O
confused	O
with	O
an	O
electronic	O
mail	O
system	O
used	O
for	O
delivering	O
human	O
readable	O
text	O
messages	O
to	O
individual	O
people	O
.	O
</s>
<s>
An	O
example	O
of	O
a	O
specific	O
application	B-Application
programming	I-Application
interface	I-Application
(	O
API	B-Application
)	O
that	O
implements	O
an	O
enterprise	B-Application
messaging	I-Application
system	I-Application
is	O
the	O
Java	B-Language
Message	I-Language
Service	I-Language
.	O
</s>
<s>
Although	O
this	O
is	O
an	O
API	B-Application
it	O
embodies	O
many	O
of	O
the	O
same	O
issues	O
involved	O
in	O
setting	O
up	O
a	O
full	O
EMS	O
.	O
</s>
<s>
These	O
policy	O
statements	O
can	O
be	O
expressed	O
in	O
the	O
XML	B-Protocol
Access	O
Control	O
Markup	O
Language	O
(	O
XACML	O
)	O
.	O
</s>
