<s>
Event	B-Algorithm
partitioning	I-Algorithm
is	O
an	O
easy-to-apply	O
systems	O
analysis	O
technique	O
that	O
helps	O
the	O
analyst	O
organize	O
requirements	O
for	O
large	O
systems	O
into	O
a	O
collection	O
of	O
smaller	O
,	O
simpler	O
,	O
minimally-connected	O
,	O
easier-to-understand	O
"	O
mini	O
systems	O
"	O
/	O
use	B-Architecture
cases	I-Architecture
.	O
</s>
<s>
A	O
brief	O
version	O
of	O
the	O
approach	O
is	O
described	O
in	O
the	O
article	O
on	O
Data	B-Application
Flow	I-Application
Diagrams	I-Application
(	O
DFDs	O
)	O
.	O
</s>
<s>
The	O
description	O
focuses	O
on	O
using	O
the	O
technique	O
to	O
create	O
data	B-Application
flow	I-Application
diagrams	I-Application
,	O
but	O
it	O
can	O
be	O
used	O
to	O
identify	O
use	B-Architecture
cases	I-Architecture
as	O
well	O
.	O
</s>
<s>
The	O
premise	O
of	O
event	B-Algorithm
partitioning	I-Algorithm
is	O
that	O
systems	O
exist	O
to	O
respond	O
to	O
external	B-Application
events	I-Application
:	O
identify	O
what	O
happens	O
in	O
the	O
business	O
environment	O
that	O
requires	O
planned	O
responses	O
,	O
then	O
define	O
and	O
build	O
systems	O
to	O
respond	O
according	O
to	O
the	O
rules	O
of	O
the	O
business	O
.	O
</s>
<s>
A	O
customer	O
,	O
in	O
the	O
jargon	O
of	O
the	O
Unified	B-Language
Modeling	I-Language
Language	I-Language
(	O
UML	B-Language
)	O
,	O
is	O
an	O
"	O
actor	B-Language
"	O
.	O
</s>
<s>
Identify	O
the	O
external	O
systems	O
by	O
brainstorming	O
a	O
list	O
of	O
the	O
"	O
actors	O
"	O
(	O
external	O
systems	O
)	O
,	O
which	O
are	O
the	O
sources	O
of	O
external	B-Application
events	I-Application
.	O
</s>
<s>
If	O
you	O
find	O
a	O
graphic	O
to	O
be	O
helpful	O
,	O
create	O
a	O
context	B-Application
diagram	I-Application
showing	O
the	O
actors	O
outside	O
of	O
the	O
system	O
under	O
study	O
and	O
the	O
flows/signals	O
between	O
them	O
.	O
</s>
<s>
Putting	O
oneself	O
in	B-Language
the	I-Language
shoes	I-Language
of	O
an	O
"	O
actor	B-Language
"	O
(	O
or	O
working	O
with	O
actor	B-Language
representatives	O
)	O
,	O
brainstorm	O
a	O
list	O
of	O
the	O
"	O
external	B-Application
events	I-Application
"	O
/	O
"	O
triggers	O
"	O
that	O
they	O
want	O
the	O
system	O
to	O
have	O
a	O
planned	O
response	O
to	O
.	O
</s>
<s>
(	O
Note	O
that	O
the	O
system	O
cannot	O
originate	O
external	B-Application
events	I-Application
;	O
only	O
an	O
actor	B-Language
can	O
.	O
)	O
</s>
<s>
Identify	O
what	O
will	O
enable	O
the	O
system	O
to	O
detect	O
the	O
external	B-Application
events	I-Application
:	O
</s>
<s>
*	O
...	O
*	O
Anything	O
between	O
single	O
asterisks	B-Language
is	O
regarded	O
as	O
a	O
comment	O
.	O
</s>
<s>
Actor	B-Language
2	O
.	O
</s>
<s>
This	O
approach	O
helps	O
the	O
analyst	O
to	O
decompose	B-Algorithm
the	O
system	O
into	O
"	O
mentally	O
bite-sized	O
"	O
mini-systems	O
using	O
events	O
that	O
require	O
a	O
planned	O
response	O
.	O
</s>
<s>
The	O
level	O
of	O
detail	O
of	O
each	O
response	O
is	O
at	O
the	O
level	O
of	O
"	O
primary	O
use	B-Architecture
cases	I-Architecture
"	O
.	O
</s>
<s>
Each	O
planned	O
response	O
may	O
be	O
modelled	O
using	O
DFD	O
notation	O
or	O
as	O
a	O
single	O
use	B-Architecture
case	I-Architecture
using	O
use	B-Language
case	I-Language
diagram	I-Language
notation	O
.	O
</s>
<s>
The	O
basic	O
flow	O
within	O
a	O
process	O
or	O
use	B-Architecture
case	I-Architecture
can	O
usually	O
be	O
described	O
in	O
a	O
relatively	O
small	O
number	O
of	O
steps	O
,	O
often	O
fewer	O
than	O
twenty	O
or	O
thirty	O
,	O
possibly	O
using	O
something	O
like	O
"	O
structured	B-Language
English	I-Language
"	O
.	O
</s>
<s>
Alternatively	O
,	O
using	O
the	O
notations	O
of	O
structured	O
techniques	O
,	O
an	O
analyst	O
could	O
create	O
a	O
"	O
Nassi	B-Application
–	I-Application
Shneiderman	I-Application
diagram	I-Application
"	O
.	O
</s>
<s>
In	O
the	O
UML	B-Language
,	O
the	O
use	B-Architecture
case	I-Architecture
could	O
be	O
modelled	O
using	O
an	O
activity	O
diagram	O
,	O
a	O
sequence	O
diagram	O
,	O
or	O
a	O
communication	O
diagram	O
.	O
</s>
<s>
This	O
could	O
be	O
problematic	O
if	O
there	O
are	O
many	O
complex	O
scenarios	O
of	O
the	O
use	B-Architecture
case	I-Architecture
;	O
the	O
analyst	O
may	O
wish	O
to	O
model	O
all	O
or	O
most	O
of	O
the	O
scenarios	O
.	O
</s>
<s>
If	O
the	O
response	O
is	O
lengthy	O
or	O
complex	O
(	O
i.e.	O
,	O
more	O
than	O
a	O
page	O
of	O
text	O
)	O
,	O
an	O
analyst	O
may	O
decompose	B-Algorithm
(	O
"	O
factor	O
out	O
"	O
or	O
deduplicate	O
)	O
into	O
smaller	O
"	O
secondary	O
use	B-Architecture
cases	I-Architecture
"	O
to	O
keep	O
the	O
"	O
parent	O
"	O
primary	O
use	B-Architecture
case	I-Architecture
smaller	O
and	O
simpler	O
.	O
</s>
<s>
These	O
secondary	O
use	B-Architecture
cases	I-Architecture
may	O
prove	O
to	O
be	O
reusable	O
as	O
well	O
.	O
</s>
<s>
(	O
In	O
a	O
UML	B-Language
use	B-Language
case	I-Language
diagram	I-Language
,	O
they	O
would	O
be	O
drawn	O
as	O
extended	O
or	O
included	O
use	B-Architecture
cases	I-Architecture
,	O
which	O
are	O
related	O
to	O
one	O
or	O
more	O
primary	O
use	B-Architecture
cases	I-Architecture
.	O
)	O
</s>
<s>
While	O
describing	O
a	O
use	B-Architecture
case	I-Architecture
,	O
an	O
analyst	O
may	O
also	O
uncover	O
"	O
business	O
rules	O
"	O
.	O
</s>
<s>
Some	O
analysts	O
suggest	O
capturing	O
business	O
rules	O
in	O
a	O
separate	O
document	O
using	O
the	O
Object	B-Language
Constraint	I-Language
Language	I-Language
or	O
some	O
other	O
formal	O
notation	O
.	O
</s>
<s>
Then	O
when	O
a	O
business	O
rule	O
must	O
be	O
obeyed	O
in	O
a	O
use	B-Architecture
case	I-Architecture
,	O
the	O
analyst	O
makes	O
reference	O
to	O
it	O
.	O
</s>
<s>
In	O
addition	O
to	O
functional	O
requirements	O
captured	O
in	O
a	O
use	B-Architecture
case	I-Architecture
description	O
,	O
an	O
analyst	O
may	O
include	O
such	O
non-functional	O
requirements	O
as	O
response	O
time	O
,	O
learnability	O
,	O
etc	O
.	O
</s>
