<s>
Syntactic	B-Algorithm
pattern	I-Algorithm
recognition	I-Algorithm
or	O
structural	B-Algorithm
pattern	I-Algorithm
recognition	I-Algorithm
is	O
a	O
form	O
of	O
pattern	O
recognition	O
,	O
in	O
which	O
each	O
object	O
can	O
be	O
represented	O
by	O
a	O
variable-cardinality	O
set	O
of	O
symbolic	O
,	O
nominal	O
features	O
.	O
</s>
<s>
This	O
allows	O
for	O
representing	O
pattern	O
structures	O
,	O
taking	O
into	O
account	O
more	O
complex	O
interrelationships	O
between	O
attributes	O
than	O
is	O
possible	O
in	O
the	O
case	O
of	O
flat	O
,	O
numerical	O
feature	B-Algorithm
vectors	I-Algorithm
of	O
fixed	O
dimensionality	O
,	O
that	O
are	O
used	O
in	O
statistical	B-General_Concept
classification	I-General_Concept
.	O
</s>
<s>
Syntactic	B-Algorithm
pattern	I-Algorithm
recognition	I-Algorithm
can	O
be	O
used	O
instead	O
of	O
statistical	O
pattern	O
recognition	O
if	O
there	O
is	O
clear	O
structure	O
in	O
the	O
patterns	O
.	O
</s>
<s>
An	O
example	O
of	O
this	O
would	O
be	O
diagnosis	O
of	O
the	O
heart	O
with	O
ECG	B-Application
measurements	O
.	O
</s>
<s>
ECG	B-Application
waveforms	O
can	O
be	O
approximated	O
with	O
diagonal	O
and	O
vertical	O
line	O
segments	O
.	O
</s>
<s>
If	O
normal	O
and	O
unhealthy	O
waveforms	O
can	O
be	O
described	O
as	O
formal	O
grammars	O
,	O
measured	O
ECG	B-Application
signal	O
can	O
be	O
classified	O
as	O
healthy	O
or	O
unhealthy	O
by	O
first	O
describing	O
it	O
in	O
term	O
of	O
the	O
basic	O
line	O
segments	O
and	O
then	O
trying	O
to	O
parse	O
the	O
descriptions	O
according	O
to	O
the	O
grammars	O
.	O
</s>
<s>
Another	O
example	O
is	O
tessellation	B-Algorithm
of	O
tiling	O
patterns	O
.	O
</s>
<s>
For	O
example	O
,	O
syntactic	B-Algorithm
pattern	I-Algorithm
recognition	I-Algorithm
can	O
be	O
used	O
to	O
find	O
out	O
what	O
objects	O
are	O
present	O
in	O
an	O
image	O
.	O
</s>
<s>
A	O
graph	B-General_Concept
matching	I-General_Concept
algorithm	O
will	O
yield	O
the	O
optimal	O
correspondence	O
.	O
</s>
