<s>
An	O
entity	B-Architecture
–	I-Architecture
relationship	I-Architecture
model	I-Architecture
(	O
or	O
ER	B-Architecture
model	I-Architecture
)	O
describes	O
interrelated	O
things	O
of	O
interest	O
in	O
a	O
specific	O
domain	O
of	O
knowledge	O
.	O
</s>
<s>
A	O
basic	O
ER	B-Architecture
model	I-Architecture
is	O
composed	O
of	O
entity	O
types	O
(	O
which	O
classify	O
the	O
things	O
of	O
interest	O
)	O
and	O
specifies	O
relationships	O
that	O
can	O
exist	O
between	O
entities	O
(	O
instances	O
of	O
those	O
entity	O
types	O
)	O
.	O
</s>
<s>
In	O
software	B-General_Concept
engineering	I-General_Concept
,	O
an	O
ER	B-Architecture
model	I-Architecture
is	O
commonly	O
formed	O
to	O
represent	O
things	O
a	O
business	O
needs	O
to	O
remember	O
in	O
order	O
to	O
perform	O
business	O
processes	O
.	O
</s>
<s>
Consequently	O
,	O
the	O
ER	B-Architecture
model	I-Architecture
becomes	O
an	O
abstract	O
data	B-Application
model	I-Application
,	O
that	O
defines	O
a	O
data	O
or	O
information	O
structure	O
which	O
can	O
be	O
implemented	O
in	O
a	O
database	O
,	O
typically	O
a	O
relational	B-Application
database	I-Application
.	O
</s>
<s>
Entity	O
–	O
relationship	O
modeling	O
was	O
developed	O
for	O
database	O
and	O
design	O
by	O
Peter	O
Chen	O
and	O
published	O
in	O
a	O
1976	O
paper	O
,	O
with	O
variants	O
of	O
the	O
idea	O
existing	O
previously	O
,	O
but	O
today	O
it	O
is	O
commonly	O
used	O
for	O
teaching	O
students	O
the	O
basics	O
of	O
data	B-Application
base	I-Application
structure	O
.	O
</s>
<s>
Some	O
ER	B-Architecture
models	I-Architecture
show	O
super	O
and	O
subtype	O
entities	O
connected	O
by	O
generalization-specialization	O
relationships	O
,	O
and	O
an	O
ER	B-Architecture
model	I-Architecture
can	O
be	O
used	O
also	O
in	O
the	O
specification	O
of	O
domain-specific	O
ontologies	O
.	O
</s>
<s>
It	O
is	O
usually	O
drawn	O
in	O
a	O
graphical	O
form	O
as	O
boxes	O
(	O
entities	O
)	O
that	O
are	O
connected	O
by	O
lines	O
(	O
relationships	O
)	O
which	O
express	B-Application
the	O
associations	O
and	O
dependencies	O
between	O
entities	O
.	O
</s>
<s>
Entities	O
may	O
be	O
characterized	O
not	O
only	O
by	O
relationships	O
,	O
but	O
also	O
by	O
additional	O
properties	O
(	O
attributes	O
)	O
,	O
which	O
include	O
identifiers	O
called	O
"	O
primary	B-Application
keys	I-Application
"	O
.	O
</s>
<s>
Diagrams	O
created	O
to	O
represent	O
attributes	O
as	O
well	O
as	O
entities	O
and	O
relationships	O
may	O
be	O
called	O
entity-attribute-relationship	O
diagrams	O
,	O
rather	O
than	O
entity	B-Architecture
–	I-Architecture
relationship	I-Architecture
models	I-Architecture
.	O
</s>
<s>
An	O
ER	B-Architecture
model	I-Architecture
is	O
typically	O
implemented	O
as	O
a	O
database	O
.	O
</s>
<s>
In	O
a	O
simple	O
relational	B-Application
database	I-Application
implementation	O
,	O
each	O
row	O
of	O
a	O
table	O
represents	O
one	O
instance	O
of	O
an	O
entity	O
type	O
,	O
and	O
each	O
field	O
in	O
a	O
table	O
represents	O
an	O
attribute	O
type	O
.	O
</s>
<s>
In	O
a	O
relational	B-Application
database	I-Application
a	O
relationship	O
between	O
entities	O
is	O
implemented	O
by	O
storing	O
the	O
primary	B-Application
key	I-Application
of	O
one	O
entity	O
as	O
a	O
pointer	O
or	O
"	O
foreign	B-Application
key	I-Application
"	O
in	O
the	O
table	O
of	O
another	O
entity	O
.	O
</s>
<s>
Note	O
that	O
the	O
conceptual-logical-physical	O
hierarchy	O
below	O
is	O
used	O
in	O
other	O
kinds	O
of	O
specification	O
,	O
and	O
is	O
different	O
from	O
the	O
three	B-Application
schema	I-Application
approach	I-Application
to	O
software	B-General_Concept
engineering	I-General_Concept
.	O
</s>
<s>
This	O
is	O
the	O
highest	O
level	O
ER	B-Architecture
model	I-Architecture
in	O
that	O
it	O
contains	O
the	O
least	O
granular	O
detail	O
but	O
establishes	O
the	O
overall	O
scope	O
of	O
what	O
is	O
to	O
be	O
included	O
within	O
the	O
model	O
set	O
.	O
</s>
<s>
The	O
conceptual	O
ER	B-Architecture
model	I-Architecture
normally	O
defines	O
master	O
reference	O
data	O
entities	O
that	O
are	O
commonly	O
used	O
by	O
the	O
organization	O
.	O
</s>
<s>
Developing	O
an	O
enterprise-wide	O
conceptual	O
ER	B-Architecture
model	I-Architecture
is	O
useful	O
to	O
support	O
documenting	O
the	O
data	B-General_Concept
architecture	I-General_Concept
for	O
an	O
organization	O
.	O
</s>
<s>
A	O
conceptual	O
ER	B-Architecture
model	I-Architecture
may	O
be	O
used	O
as	O
the	O
foundation	O
for	O
one	O
or	O
more	O
logical	B-Application
data	I-Application
models	I-Application
(	O
see	O
below	O
)	O
.	O
</s>
<s>
The	O
purpose	O
of	O
the	O
conceptual	O
ER	B-Architecture
model	I-Architecture
is	O
then	O
to	O
establish	O
structural	O
metadata	O
commonality	O
for	O
the	O
master	B-General_Concept
data	I-General_Concept
entities	O
between	O
the	O
set	O
of	O
logical	O
ER	B-Architecture
models	I-Architecture
.	O
</s>
<s>
The	O
conceptual	B-Application
data	I-Application
model	I-Application
may	O
be	O
used	O
to	O
form	O
commonality	O
relationships	O
between	O
ER	B-Architecture
models	I-Architecture
as	O
a	O
basis	O
for	O
data	B-Application
model	I-Application
integration	O
.	O
</s>
<s>
A	O
logical	O
ER	B-Architecture
model	I-Architecture
does	O
not	O
require	O
a	O
conceptual	O
ER	B-Architecture
model	I-Architecture
,	O
especially	O
if	O
the	O
scope	O
of	O
the	O
logical	O
ER	B-Architecture
model	I-Architecture
includes	O
only	O
the	O
development	O
of	O
a	O
distinct	O
information	O
system	O
.	O
</s>
<s>
The	O
logical	O
ER	B-Architecture
model	I-Architecture
contains	O
more	O
detail	O
than	O
the	O
conceptual	O
ER	B-Architecture
model	I-Architecture
.	O
</s>
<s>
In	O
addition	O
to	O
master	B-General_Concept
data	I-General_Concept
entities	O
,	O
operational	O
and	O
transactional	O
data	O
entities	O
are	O
now	O
defined	O
.	O
</s>
<s>
The	O
logical	O
ER	B-Architecture
model	I-Architecture
is	O
however	O
developed	O
independently	O
of	O
the	O
specific	O
database	B-Application
management	I-Application
system	I-Application
into	O
which	O
it	O
can	O
be	O
implemented	O
.	O
</s>
<s>
One	O
or	O
more	O
physical	O
ER	B-Architecture
models	I-Architecture
may	O
be	O
developed	O
from	O
each	O
logical	O
ER	B-Architecture
model	I-Architecture
.	O
</s>
<s>
The	O
physical	O
ER	B-Architecture
model	I-Architecture
is	O
normally	O
developed	O
to	O
be	O
instantiated	O
as	O
a	O
database	O
.	O
</s>
<s>
Therefore	O
,	O
each	O
physical	O
ER	B-Architecture
model	I-Architecture
must	O
contain	O
enough	O
detail	O
to	O
produce	O
a	O
database	O
and	O
each	O
physical	O
ER	B-Architecture
model	I-Architecture
is	O
technology	O
dependent	O
since	O
each	O
database	B-Application
management	I-Application
system	I-Application
is	O
somewhat	O
different	O
.	O
</s>
<s>
The	O
physical	O
model	O
is	O
normally	O
instantiated	O
in	O
the	O
structural	O
metadata	O
of	O
a	O
database	B-Application
management	I-Application
system	I-Application
as	O
relational	B-Application
database	I-Application
objects	O
such	O
as	O
database	B-Application
tables	I-Application
,	O
database	B-Data_Structure
indexes	I-Data_Structure
such	O
as	O
unique	B-Application
key	I-Application
indexes	O
,	O
and	O
database	O
constraints	O
such	O
as	O
a	O
foreign	B-Application
key	I-Application
constraint	I-Application
or	O
a	O
commonality	O
constraint	O
.	O
</s>
<s>
The	O
ER	B-Architecture
model	I-Architecture
is	O
also	O
normally	O
used	O
to	O
design	O
modifications	O
to	O
the	O
relational	B-Application
database	I-Application
objects	O
and	O
to	O
maintain	O
the	O
structural	O
metadata	O
of	O
the	O
database	O
.	O
</s>
<s>
The	O
data	B-Application
modeling	I-Application
technique	O
can	O
be	O
used	O
to	O
describe	O
any	O
ontology	O
(	O
i.e.	O
</s>
<s>
an	O
overview	O
and	O
classifications	O
of	O
used	O
terms	O
and	O
their	O
relationships	O
)	O
for	O
a	O
certain	O
area	B-Algorithm
of	I-Algorithm
interest	I-Algorithm
.	O
</s>
<s>
In	O
the	O
case	B-Application
of	O
the	O
design	O
of	O
an	O
information	O
system	O
that	O
is	O
based	O
on	O
a	O
database	O
,	O
the	O
conceptual	B-Application
data	I-Application
model	I-Application
is	O
,	O
at	O
a	O
later	O
stage	O
(	O
usually	O
called	O
logical	O
design	O
)	O
,	O
mapped	O
to	O
a	O
logical	B-Application
data	I-Application
model	I-Application
,	O
such	O
as	O
the	O
relational	B-Architecture
model	I-Architecture
;	O
this	O
in	O
turn	O
is	O
mapped	O
to	O
a	O
physical	O
model	O
during	O
physical	O
design	O
.	O
</s>
<s>
The	O
model	O
's	O
linguistic	O
aspect	O
described	O
above	O
is	O
utilized	O
in	O
the	O
declarative	B-Language
database	B-Language
query	I-Language
language	I-Language
ERROL	O
,	O
which	O
mimics	O
natural	O
language	O
constructs	O
.	O
</s>
<s>
ERROL	O
's	O
semantics	B-Application
and	O
implementation	O
are	O
based	O
on	O
reshaped	O
relational	B-Algorithm
algebra	I-Algorithm
(	O
RRA	O
)	O
,	O
a	O
relational	B-Algorithm
algebra	I-Algorithm
that	O
is	O
adapted	O
to	O
the	O
entity	B-Architecture
–	I-Architecture
relationship	I-Architecture
model	I-Architecture
and	O
captures	O
its	O
linguistic	O
aspect	O
.	O
</s>
<s>
All	O
entities	O
except	O
weak	B-Application
entities	I-Application
must	O
have	O
a	O
minimal	O
set	O
of	O
uniquely	O
identifying	O
attributes	O
which	O
may	O
be	O
used	O
as	O
a	O
unique/primary	O
key	O
.	O
</s>
<s>
Entity-relationship	B-Architecture
diagrams	I-Architecture
(	O
ERDs	O
)	O
do	O
n't	O
show	O
single	O
entities	O
or	O
single	O
instances	O
of	O
relations	O
.	O
</s>
<s>
In	O
other	O
words	O
,	O
a	O
relationship	O
set	O
corresponds	O
to	O
a	O
relation	B-Algorithm
in	I-Algorithm
mathematics	I-Algorithm
,	O
while	O
a	O
relationship	O
corresponds	O
to	O
a	O
member	O
of	O
the	O
relation	O
.	O
</s>
<s>
Certain	O
cardinality	B-Application
constraints	O
on	O
relationship	O
sets	O
may	O
be	O
indicated	O
as	O
well	O
.	O
</s>
<s>
Chen	O
proposed	O
the	O
following	O
guiding	O
rules	O
for	O
mapping	O
natural	O
language	O
descriptions	O
into	O
ER	B-Architecture
diagrams	I-Architecture
:	O
by	O
Peter	O
Chen	O
.	O
</s>
<s>
The	O
lines	O
,	O
arrows	O
and	O
crow's-feet	O
of	O
some	O
diagrams	O
owes	O
more	O
to	O
the	O
earlier	O
Bachman	B-Application
diagrams	I-Application
than	O
to	O
Chen	O
's	O
relationship	O
diagrams	O
.	O
</s>
<s>
Correct	O
nouns	O
in	O
this	O
case	B-Application
are	O
owner	O
and	O
possession	O
.	O
</s>
<s>
Chen	O
described	O
look-across	O
cardinalities	B-Application
.	O
</s>
<s>
As	O
an	O
aside	O
,	O
the	O
Barker	B-Application
–	I-Application
Ellis	I-Application
notation	O
,	O
used	O
in	O
Oracle	B-Application
Designer	O
,	O
uses	O
same-side	O
for	O
minimum	O
cardinality	B-Application
(	O
analogous	O
to	O
optionality	O
)	O
and	O
role	O
,	O
but	O
look-across	O
for	O
maximum	O
cardinality	B-Application
(	O
the	O
crows	O
foot	O
)	O
.	O
</s>
<s>
In	O
Merise	B-General_Concept
,	O
Elmasri	O
&	O
Navathe	O
and	O
others	O
there	O
is	O
a	O
preference	O
for	O
same-side	O
for	O
roles	O
and	O
both	O
minimum	O
and	O
maximum	O
cardinalities	B-Application
.	O
</s>
<s>
one	O
reads	O
"	O
A	O
'	O
look	O
across	O
 '	O
notation	O
such	O
as	O
used	O
in	O
the	O
UML	B-Language
does	O
not	O
effectively	O
represent	O
the	O
semantics	B-Application
of	O
participation	O
constraints	O
imposed	O
on	O
relationships	O
where	O
the	O
degree	O
is	O
higher	O
than	O
binary.	O
"	O
</s>
<s>
In	O
Feinerer	O
it	O
says	O
"	O
Problems	O
arise	O
if	O
we	O
operate	O
under	O
the	O
look-across	O
semantics	B-Application
as	O
used	O
for	O
UML	B-Language
associations	O
.	O
</s>
<s>
Chen	B-Architecture
's	I-Architecture
notation	I-Architecture
for	O
entity	O
–	O
relationship	O
modeling	O
uses	O
rectangles	O
to	O
represent	O
entity	O
sets	O
,	O
and	O
diamonds	O
to	O
represent	O
relationships	O
appropriate	O
for	O
first-class	O
objects	O
:	O
they	O
can	O
have	O
attributes	O
and	O
relationships	O
of	O
their	O
own	O
.	O
</s>
<s>
Cardinality	B-Application
constraints	O
are	O
expressed	O
as	O
follows	O
:	O
</s>
<s>
a	O
double	O
line	O
indicates	O
a	O
participation	O
constraint	O
,	O
totality	O
or	O
surjectivity	B-Algorithm
:	O
all	O
entities	O
in	O
the	O
entity	O
set	O
must	O
participate	O
in	O
at	O
least	O
one	O
relationship	O
in	O
the	O
relationship	O
set	O
;	O
</s>
<s>
an	O
arrow	O
from	O
entity	O
set	O
to	O
relationship	O
set	O
indicates	O
a	O
key	B-Application
constraint	I-Application
,	O
i.e.	O
</s>
<s>
bijectivity	B-Algorithm
:	O
each	O
entity	O
in	O
the	O
entity	O
set	O
is	O
involved	O
in	O
exactly	O
one	O
relationship	O
.	O
</s>
<s>
an	O
underlined	O
name	O
of	O
an	O
attribute	O
indicates	O
that	O
it	O
is	O
a	O
key	B-Application
:	O
two	O
different	O
entities	O
or	O
relationships	O
with	O
this	O
attribute	O
always	O
have	O
different	O
values	O
for	O
this	O
attribute	O
.	O
</s>
<s>
Crow	O
's	O
foot	O
notation	O
,	O
the	O
beginning	O
of	O
which	O
dates	O
back	O
to	O
an	O
article	O
by	O
Gordon	O
Everest	O
(	O
1976	O
)	O
,	O
is	O
used	O
in	O
Barker	B-Application
's	I-Application
notation	I-Application
,	O
Structured	O
Systems	O
Analysis	O
and	O
Design	O
Method	O
(	O
SSADM	O
)	O
and	O
information	B-Application
technology	I-Application
engineering	I-Application
.	O
</s>
<s>
Different	O
shapes	O
at	O
the	O
ends	O
of	O
these	O
lines	O
represent	O
the	O
relative	O
cardinality	B-Application
of	O
the	O
relationship	O
.	O
</s>
<s>
Many	O
of	O
the	O
consultants	O
at	O
CACI	O
(	O
including	O
Richard	O
Barker	O
)	O
subsequently	O
moved	O
to	O
Oracle	B-Application
UK	O
,	O
where	O
they	O
developed	O
the	O
early	O
versions	O
of	O
Oracle	B-Application
's	O
CASE	B-Application
tools	O
,	O
introducing	O
the	O
notation	O
to	O
a	O
wider	O
audience	O
.	O
</s>
<s>
Three	O
symbols	O
are	O
used	O
to	O
represent	O
cardinality	B-Application
:	O
</s>
<s>
These	O
symbols	O
are	O
used	O
in	O
pairs	O
to	O
represent	O
the	O
four	O
types	O
of	O
cardinality	B-Application
that	O
an	O
entity	O
may	O
have	O
in	O
a	O
relationship	O
.	O
</s>
<s>
The	O
issue	O
derives	O
its	O
name	O
from	O
the	O
way	O
the	O
model	O
looks	O
when	O
it	O
's	O
drawn	O
in	O
an	O
entity	B-Architecture
–	I-Architecture
relationship	I-Architecture
diagram	I-Architecture
:	O
the	O
linked	O
tables	O
'	O
fan	O
out	O
 '	O
from	O
the	O
master	O
table	O
.	O
</s>
<s>
This	O
type	O
of	O
model	O
looks	O
similar	O
to	O
a	O
star	B-Application
schema	I-Application
,	O
a	O
type	O
of	O
model	O
used	O
in	O
data	O
warehouses	O
.	O
</s>
<s>
This	O
issue	O
occurs	O
mostly	O
in	O
databases	B-Application
for	O
decision	O
support	O
systems	O
,	O
and	O
software	O
that	O
queries	O
such	O
systems	O
sometimes	O
includes	O
specific	O
methods	O
for	O
handling	O
this	O
issue	O
.	O
</s>
<s>
The	O
UML	B-Language
specification	O
explicitly	O
states	O
that	O
associations	O
in	O
class	O
models	O
are	O
extensional	O
and	O
this	O
is	O
in	O
fact	O
self-evident	O
by	O
considering	O
the	O
extensive	O
array	O
of	O
additional	O
"	O
adornments	O
"	O
provided	O
by	O
the	O
specification	O
over	O
and	O
above	O
those	O
provided	O
by	O
any	O
of	O
the	O
prior	O
candidate	O
"	O
semantic	O
modelling	O
languages	O
"	O
.	O
</s>
<s>
"	O
The	O
entity-relationship	B-Architecture
model	I-Architecture
adopts	O
the	O
more	O
natural	O
view	O
that	O
the	O
real	O
world	O
consists	O
of	O
entities	O
and	O
relationships	O
.	O
</s>
<s>
In	O
his	O
original	O
1976	O
article	O
Chen	O
explicitly	O
contrasts	O
entity	B-Architecture
–	I-Architecture
relationship	I-Architecture
diagrams	I-Architecture
with	O
record	O
modelling	O
techniques	O
:	O
</s>
<s>
"	O
The	O
data	B-Application
structure	I-Application
diagram	I-Application
is	O
a	O
representation	O
of	O
the	O
organization	O
of	O
records	O
and	O
is	O
not	O
an	O
exact	O
representation	O
of	O
entities	O
and	O
relationships.	O
"	O
</s>
<s>
Chen	O
is	O
in	O
accord	O
with	O
philosophical	O
traditions	O
from	O
the	O
time	O
of	O
the	O
Ancient	O
Greek	O
philosophers	O
:	O
Plato	B-Operating_System
and	O
Aristotle	O
.	O
</s>
<s>
Plato	B-Operating_System
himself	O
associates	O
knowledge	O
with	O
the	O
apprehension	O
of	O
unchanging	O
Forms	O
(	O
namely	O
,	O
archetypes	O
or	O
abstract	O
representations	O
of	O
the	O
many	O
types	O
of	O
things	O
,	O
and	O
properties	O
)	O
and	O
their	O
relationships	O
to	O
one	O
another	O
.	O
</s>
<s>
An	O
ER	B-Architecture
model	I-Architecture
is	O
primarily	O
conceptual	O
,	O
an	O
ontology	O
that	O
expresses	O
predicates	O
in	O
a	O
domain	O
of	O
knowledge	O
.	O
</s>
<s>
ER	B-Architecture
models	I-Architecture
are	O
readily	O
used	O
to	O
represent	O
relational	B-Application
database	I-Application
structures	O
(	O
after	O
Codd	O
and	O
Date	O
)	O
but	O
not	O
so	O
often	O
to	O
represent	O
other	O
kinds	O
of	O
data	O
structure	O
(	O
data	O
warehouses	O
,	O
document	O
stores	O
etc	O
.	O
)	O
</s>
<s>
Some	O
ER	B-Architecture
model	I-Architecture
notations	O
include	O
symbols	O
to	O
show	O
super-sub-type	O
relationships	O
and	O
mutual	O
exclusion	O
between	O
relationships	O
;	O
some	O
do	O
n't	O
.	O
</s>
<s>
An	O
ER	B-Architecture
model	I-Architecture
does	O
not	O
show	O
an	O
entity	O
's	O
life	O
history	O
(	O
how	O
its	O
attributes	O
and/or	O
relationships	O
change	O
over	O
time	O
in	O
response	O
to	O
events	O
)	O
.	O
</s>
<s>
Some	O
have	O
extended	O
ER	O
modeling	O
with	O
constructs	O
to	O
represent	O
state	O
changes	O
,	O
an	O
approach	O
supported	O
by	O
the	O
original	O
author	O
;	O
an	O
example	O
is	O
Anchor	B-Application
Modeling	I-Application
.	O
</s>
<s>
Many	O
other	O
kinds	O
of	O
diagram	O
are	O
drawn	O
to	O
model	O
other	O
aspects	O
of	O
systems	O
,	O
including	O
the	O
14	O
diagram	O
types	O
offered	O
by	O
UML	B-Language
.	O
</s>
<s>
Today	O
,	O
even	O
where	O
ER	O
modeling	O
could	O
be	O
useful	O
,	O
it	O
is	O
uncommon	O
because	O
many	O
use	O
tools	O
that	O
support	O
similar	O
kinds	O
of	O
model	O
,	O
notably	O
class	O
diagrams	O
for	O
OO	O
programming	O
and	O
data	O
models	O
for	O
relational	B-Application
database	I-Application
management	O
systems	O
.	O
</s>
<s>
The	O
enhanced	B-Application
entity	I-Application
–	I-Application
relationship	I-Application
model	I-Application
(	O
EER	O
modeling	O
)	O
introduces	O
several	O
concepts	O
not	O
in	O
ER	O
modeling	O
,	O
but	O
are	O
closely	O
related	O
to	O
object-oriented	B-Language
design	O
,	O
like	O
is-a	O
relationships	O
.	O
</s>
<s>
For	O
modelling	O
temporal	O
databases	B-Application
,	O
numerous	O
ER	O
extensions	O
have	O
been	O
considered	O
.	O
</s>
<s>
Similarly	O
,	O
the	O
ER	B-Architecture
model	I-Architecture
was	O
found	O
unsuitable	O
for	O
multidimensional	O
databases	B-Application
(	O
used	O
in	O
OLAP	B-Application
applications	O
)	O
;	O
no	O
dominant	O
conceptual	O
model	O
has	O
emerged	O
in	O
this	O
field	O
yet	O
,	O
although	O
they	O
generally	O
revolve	O
around	O
the	O
concept	O
of	O
OLAP	B-Application
cube	O
(	O
also	O
known	O
as	O
data	B-Algorithm
cube	I-Algorithm
within	O
the	O
field	O
)	O
.	O
</s>
