<s>
An	O
enterprise	B-Application
service	I-Application
bus	I-Application
(	O
ESB	O
)	O
implements	O
a	O
communication	O
system	O
between	O
mutually	O
interacting	O
software	O
applications	O
in	O
a	O
service-oriented	O
architecture	O
(	O
SOA	O
)	O
.	O
</s>
<s>
It	O
represents	O
a	O
software	B-Architecture
architecture	I-Architecture
for	O
distributed	B-Architecture
computing	I-Architecture
,	O
and	O
is	O
a	O
special	O
variant	O
of	O
the	O
more	O
general	O
client-server	B-Operating_System
model	I-Operating_System
,	O
wherein	O
any	O
application	O
may	O
behave	O
as	O
server	O
or	O
client	O
.	O
</s>
<s>
Its	O
primary	O
use	O
is	O
in	O
enterprise	B-Architecture
application	I-Architecture
integration	I-Architecture
(	O
EAI	B-Architecture
)	O
of	O
heterogeneous	O
and	O
complex	O
service	O
landscapes	O
.	O
</s>
<s>
The	O
concept	O
of	O
the	O
enterprise	B-Application
service	I-Application
bus	I-Application
is	O
analogous	O
to	O
the	O
bus	B-General_Concept
concept	O
found	O
in	O
computer	B-General_Concept
hardware	I-General_Concept
architecture	I-General_Concept
combined	O
with	O
the	O
modular	O
and	O
concurrent	O
design	O
of	O
high-performance	O
computer	B-General_Concept
operating	I-General_Concept
systems	I-General_Concept
.	O
</s>
<s>
No	O
global	O
standards	O
exist	O
for	O
enterprise	B-Application
service	I-Application
bus	I-Application
concepts	O
or	O
implementations	O
.	O
</s>
<s>
Most	O
providers	O
of	O
message-oriented	B-Application
middleware	I-Application
have	O
adopted	O
the	O
enterprise	B-Application
service	I-Application
bus	I-Application
concept	O
as	O
de	O
facto	O
standard	O
for	O
a	O
service-oriented	O
architecture	O
.	O
</s>
<s>
The	O
implementations	O
of	O
ESB	O
use	O
event-driven	B-Application
and	O
standards-based	O
message-oriented	B-Application
middleware	I-Application
in	O
combination	O
with	O
message	B-Operating_System
queues	I-Operating_System
as	O
technology	O
frameworks	O
.	O
</s>
<s>
However	O
,	O
some	O
software	O
manufacturers	O
relabel	O
existing	O
middleware	O
and	O
communication	O
solutions	O
as	O
ESB	O
without	O
adopting	O
the	O
crucial	O
aspect	O
of	O
a	O
bus	B-General_Concept
concept	O
.	O
</s>
<s>
An	O
ESB	O
applies	O
the	O
design	O
concept	O
of	O
modern	O
operating	B-General_Concept
systems	I-General_Concept
to	O
independent	O
services	O
running	O
within	O
networks	O
of	O
disparate	O
and	O
independent	O
computers	O
.	O
</s>
<s>
Like	O
concurrent	O
operating	B-General_Concept
systems	I-General_Concept
,	O
an	O
ESB	O
provides	O
commodity	O
services	O
in	O
addition	O
to	O
adoption	O
,	O
translation	O
and	O
routing	O
of	O
client	O
requests	O
to	O
appropriate	O
answering	O
services	O
.	O
</s>
<s>
Provide	O
commodity	O
services	O
like	O
event	O
handling	O
,	O
data	O
transformation	O
and	O
mapping	O
,	O
message	O
and	O
event	O
queuing	O
and	O
sequencing	O
,	O
security	O
or	O
exception	B-General_Concept
handling	I-General_Concept
,	O
protocol	O
conversion	O
and	O
enforcing	O
proper	O
quality	O
of	O
communication	O
service	O
.	O
</s>
<s>
The	O
first	O
published	O
usage	O
of	O
the	O
term	O
"	O
enterprise	B-Application
service	I-Application
bus	I-Application
"	O
is	O
attributed	O
to	O
Roy	O
W	O
.	O
Schulte	O
from	O
the	O
Gartner	O
Group	O
2002	O
and	O
the	O
book	O
The	O
Enterprise	B-Application
Service	I-Application
Bus	I-Application
by	O
David	O
Chappell	O
.	O
</s>
<s>
Ideally	O
,	O
the	O
ESB	O
should	O
be	O
able	O
to	O
replace	O
all	O
direct	O
contact	O
with	O
the	O
applications	O
on	O
the	O
bus	B-General_Concept
,	O
so	O
that	O
all	O
communication	O
takes	O
place	O
via	O
the	O
ESB	O
.	O
</s>
<s>
To	O
achieve	O
this	O
objective	O
,	O
the	O
ESB	O
must	O
encapsulate	B-Application
the	O
functionality	O
offered	O
by	O
its	O
component	O
applications	O
in	O
a	O
meaningful	O
way	O
.	O
</s>
<s>
This	O
typically	O
occurs	O
through	O
the	O
use	O
of	O
an	O
enterprise	B-Application
message	I-Application
model	I-Application
.	O
</s>
<s>
A	O
software	O
adapter	B-Device
fulfills	O
the	O
task	O
of	O
effecting	O
these	O
transformations	O
,	O
analogously	O
to	O
a	O
physical	O
adapter	B-Device
.	O
</s>
<s>
ESBs	O
rely	O
on	O
accurately	O
constructing	O
the	O
enterprise	B-Application
message	I-Application
model	I-Application
and	O
properly	O
designing	O
the	O
functionality	O
offered	O
by	O
applications	O
.	O
</s>
<s>
If	O
the	O
message	O
model	O
does	O
not	O
completely	O
encapsulate	B-Application
the	O
application	O
functionality	O
,	O
then	O
other	O
applications	O
that	O
desire	O
that	O
functionality	O
may	O
have	O
to	O
bypass	O
the	O
bus	B-General_Concept
,	O
and	O
invoke	O
the	O
mismatched	O
applications	O
directly	O
.	O
</s>
<s>
The	O
beauty	O
of	O
the	O
ESB	O
lies	O
in	O
its	O
platform-agnostic	O
nature	O
and	O
the	O
ability	O
to	O
integrate	O
with	O
anything	O
at	O
any	O
condition	O
.	O
</s>
<s>
It	O
is	O
important	O
that	O
Application	O
Lifecycle	O
Management	B-Application
vendors	O
truly	O
apply	O
all	O
the	O
ESB	O
capabilities	O
in	O
their	O
integration	O
products	O
while	O
adopting	O
SOA	O
.	O
</s>
<s>
Therefore	O
,	O
the	O
challenges	O
and	O
opportunities	O
for	O
EAI	B-Architecture
vendors	O
are	O
to	O
provide	O
an	O
integration	O
solution	O
that	O
is	O
low-cost	O
,	O
easily	O
configurable	O
,	O
intuitive	O
,	O
user-friendly	O
,	O
and	O
open	O
to	O
any	O
tools	O
customers	O
choose	O
.	O
</s>
<s>
Category	O
Functions	O
Invocation	O
support	O
for	O
synchronous	O
and	O
asynchronous	O
transport	O
protocols	O
,	O
service	O
mapping	O
(	O
locating	O
and	O
binding	O
)	O
Routing	O
addressability	O
,	O
static/deterministic	O
routing	O
,	O
content-based	O
routing	O
,	O
rules-based	O
routing	O
,	O
policy-based	O
routing	O
Mediation	O
adapters	B-Device
,	O
protocol	O
transformation	O
,	O
service	O
mapping	O
Messaging	O
message-processing	O
,	O
message	O
transformation	O
and	O
message	O
enhancement	O
Process	O
choreography¹	O
implementation	O
of	O
complex	O
business	O
processes	O
Service	O
orchestration²	O
coordination	O
of	O
multiple	O
implementation	O
services	O
exposed	O
as	O
a	O
single	O
,	O
aggregate	O
service	O
Complex	B-Operating_System
event	I-Operating_System
processing	I-Operating_System
event-interpretation	O
,	O
correlation	O
,	O
pattern-matching	O
Other	O
quality	O
of	O
service	O
security	O
(	O
encryption	O
and	O
signing	O
)	O
,	O
reliable	O
delivery	O
,	O
transaction	O
management	B-Application
Management	B-Application
monitoring	O
,	O
audit	O
,	O
logging	O
,	O
metering	O
,	O
admin	O
console	O
,	O
BAM	B-Application
(	O
BAM	B-Application
is	O
not	O
a	O
management	B-Application
capability	O
in	O
other	O
words	O
the	O
ESB	O
does	O
n't	O
react	O
to	O
a	O
specific	O
threshold	O
.	O
</s>
<s>
These	O
solutions	O
often	O
focus	O
on	O
low-level	O
ESB	O
functions	O
,	O
such	O
as	O
connectivity	O
,	O
routing	O
and	O
transformation	O
,	O
and	O
require	O
coding	O
or	O
scripting	O
to	O
implement	O
orchestration	B-Application
.	O
</s>
<s>
Developers	O
operating	O
at	O
a	O
project	O
or	O
tactical	O
level	O
,	O
e.g.	O
,	O
just	O
trying	O
to	O
fix	O
a	O
problem	O
,	O
often	O
gravitate	O
toward	O
lightweight	O
service	O
bus	B-General_Concept
technologies	O
,	O
but	O
there	O
is	O
often	O
ongoing	O
tension	O
between	O
these	O
initiatives	O
and	O
an	O
enterprise	O
architecture	O
whose	O
goal	O
it	O
is	O
to	O
optimize	O
infrastructure	O
across	O
multiple	O
projects	O
.	O
</s>
