<s>
The	O
Digital	B-General_Concept
twin	I-General_Concept
integration	I-General_Concept
level	I-General_Concept
refers	O
to	O
the	O
different	O
degrees	O
of	O
data	O
and	O
information	O
flow	O
that	O
may	O
occur	O
between	O
the	O
physical	O
part	O
and	O
the	O
digital	O
copy	O
of	O
a	O
digital	B-General_Concept
twin	I-General_Concept
.	O
</s>
<s>
According	O
to	O
the	O
different	O
levels	O
of	O
integration	O
,	O
the	O
digital	B-General_Concept
twin	I-General_Concept
can	O
be	O
divided	O
into	O
three	O
subcategories	O
:	O
Digital	O
Model	O
(	O
DM	O
)	O
,	O
Digital	O
Shadow	O
(	O
DS	O
)	O
and	O
Digital	B-General_Concept
Twin	I-General_Concept
(	O
DT	O
)	O
.	O
</s>
<s>
The	O
concept	O
of	O
Digital	B-General_Concept
Twin	I-General_Concept
is	O
now	O
increasingly	O
widespread	O
and	O
it	O
is	O
one	O
of	O
the	O
greatest	O
examples	O
of	O
digital	B-General_Concept
transformation	I-General_Concept
not	O
only	O
in	O
the	O
manufacturing	O
sector	O
but	O
also	O
in	O
the	O
construction	O
,	O
healthcare	O
and	O
automotive	O
area	O
.	O
</s>
<s>
Digital	B-General_Concept
Twin	I-General_Concept
definitions	O
vary	O
and	O
take	O
on	O
different	O
shades	O
depending	O
on	O
the	O
analysed	O
context	O
.	O
</s>
<s>
Although	O
the	O
literature	O
provides	O
a	O
common	O
view	O
of	O
the	O
digital	B-General_Concept
twin	I-General_Concept
as	O
a	O
digital	O
copy	O
of	O
a	O
physical	O
element	O
,	O
several	O
definitions	O
lead	O
the	O
concept	O
of	O
digital	B-General_Concept
twin	I-General_Concept
to	O
be	O
subjected	O
to	O
different	O
interpretations	O
and	O
misconceptions	O
.	O
</s>
<s>
For	O
example	O
,	O
some	O
authors	O
use	O
the	O
concept	O
of	O
Digital	O
Models	O
(	O
e.g.	O
,	O
3D	O
models	O
)	O
and	O
digital	B-General_Concept
twin	I-General_Concept
indistinctly	O
considering	O
them	O
as	O
interchangeable	O
.	O
</s>
<s>
However	O
,	O
a	O
significant	O
difference	O
between	O
digital	B-General_Concept
twin	I-General_Concept
and	O
digital	O
3D	O
models	O
and	O
systems	O
exists	O
and	O
can	O
be	O
outlined	O
based	O
on	O
different	O
level	O
of	O
data	B-General_Concept
integration	I-General_Concept
and	O
information	O
exchange	O
.	O
</s>
<s>
Data	O
are	O
among	O
the	O
most	O
significant	O
elements	O
of	O
a	O
digital	B-General_Concept
twin	I-General_Concept
.	O
</s>
<s>
Following	O
the	O
approach	O
of	O
Michael	O
Grieves	O
,	O
the	O
digital	B-General_Concept
twin	I-General_Concept
concept	O
model	O
is	O
composed	O
by	O
three	O
main	O
parts	O
:	O
physical	O
object	O
,	O
virtual	O
or	O
digital	O
object	O
and	O
data	O
that	O
provide	O
the	O
connection	O
between	O
the	O
physical	O
and	O
the	O
digital	O
.	O
</s>
<s>
The	O
physical	O
collects	O
and	O
stores	O
real	B-General_Concept
time	I-General_Concept
data	I-General_Concept
that	O
are	O
sent	O
to	O
digital	O
copy	O
for	O
processing	O
.	O
</s>
<s>
Vice	O
versa	O
,	O
the	O
digital	O
applies	O
its	O
imbedded	O
engineering	O
models	O
and	O
AI	B-Application
subjecting	O
data	O
to	O
transformations	O
and	O
processing	O
information	O
.	O
</s>
<s>
Depending	O
on	O
the	O
different	O
degree	O
of	O
data	B-General_Concept
integration	I-General_Concept
,	O
a	O
classification	O
of	O
the	O
digital	B-General_Concept
twin	I-General_Concept
into	O
three	O
subcategories	O
was	O
proposed	O
:	O
</s>
<s>
Digital	B-General_Concept
Twin	I-General_Concept
(	O
DT	O
)	O
.	O
</s>
<s>
The	O
digital	B-General_Concept
twin	I-General_Concept
is	O
characterised	O
by	O
a	O
bi-directional	O
data	O
flow	O
between	O
the	O
digital	O
and	O
the	O
physical	O
.	O
</s>
<s>
If	O
digital	O
representations	O
do	O
not	O
enable	O
bi-directional	O
automatic	O
data	O
exchange	O
,	O
are	O
modelled	O
manually	O
and	O
have	O
not	O
a	O
direct	O
connection	O
with	O
the	O
physical	O
object	O
,	O
these	O
cannot	O
be	O
a	O
digital	B-General_Concept
twin	I-General_Concept
but	O
rather	O
a	O
digital	O
model	O
or	O
a	O
digital	O
shadow	O
.	O
</s>
<s>
A	O
digital	O
model	O
has	O
the	O
lowest	O
level	O
of	O
data	B-General_Concept
integration	I-General_Concept
.	O
</s>
<s>
According	O
to	O
a	O
study	O
carried	O
out	O
,	O
most	O
of	O
digital	B-General_Concept
twin	I-General_Concept
research	O
articles	O
in	O
the	O
manufacturing	O
area	O
stops	O
at	O
the	O
digital	O
shadow	O
level	O
of	O
integration	O
.	O
</s>
<s>
The	O
term	O
digital	O
shadow	O
can	O
be	O
associated	O
to	O
the	O
building	B-Architecture
information	I-Architecture
modeling	I-Architecture
concept	O
in	O
the	O
construction	O
sector	O
.	O
</s>
<s>
The	O
highest	O
level	O
of	O
integration	O
is	O
reserved	O
to	O
a	O
digital	B-General_Concept
twin	I-General_Concept
.	O
</s>
<s>
Unlike	O
the	O
digital	O
shadow	O
,	O
the	O
digital	B-General_Concept
twin	I-General_Concept
enables	O
to	O
verify	O
physical	O
processes	O
and	O
activities	O
prior	O
the	O
execution	O
to	O
reduce	O
failures	O
and	O
it	O
can	O
outline	O
differences	O
between	O
the	O
actual	O
and	O
simulated	O
performances	O
to	O
optimise	O
and	O
predict	O
the	O
behaviour	O
.	O
</s>
<s>
Furthermore	O
,	O
since	O
data	O
within	O
the	O
digital	B-General_Concept
twin	I-General_Concept
are	O
derived	O
not	O
only	O
from	O
the	O
physical	O
environment	O
but	O
also	O
from	O
virtual	O
models	O
with	O
data	O
elaborated	O
through	O
processes	O
such	O
as	O
statistics	O
and	O
regression	O
,	O
the	O
digital	B-General_Concept
twin	I-General_Concept
is	O
more	O
abundant	O
in	O
data	O
than	O
the	O
digital	O
shadow	O
.	O
</s>
<s>
Applying	O
the	O
concept	O
of	O
digital	B-General_Concept
twin	I-General_Concept
to	O
the	O
construction	O
environment	O
,	O
a	O
building	O
digital	B-General_Concept
twin	I-General_Concept
is	O
not	O
limited	O
to	O
its	O
3D	O
visual	O
modeling	O
,	O
that	O
is	O
called	O
digital	O
model	O
or	O
digital	O
shadow	O
according	O
to	O
the	O
degree	O
of	O
data	B-General_Concept
integration	I-General_Concept
.	O
</s>
<s>
It	O
can	O
become	O
a	O
digital	B-General_Concept
twin	I-General_Concept
if	O
it	O
has	O
automated	O
or	O
semi-automated	O
thermal	O
management	O
control	O
,	O
or	O
the	O
procurement	O
of	O
construction	O
site	O
components	O
with	O
physical	O
delivery	O
and	O
sensor	O
devices	O
by	O
the	O
use	O
of	O
satellites	O
,	O
or	O
by	O
optimising	O
and	O
scheduling	O
the	O
renovation	O
or	O
construction	O
processes	O
using	O
connected	O
on-site	O
smart	B-Device
devices	I-Device
.	O
</s>
