<s>
Graph	B-General_Concept
matching	I-General_Concept
is	O
the	O
problem	O
of	O
finding	O
a	O
similarity	O
between	O
graphs	O
.	O
</s>
<s>
Graphs	O
are	O
commonly	O
used	O
to	O
encode	O
structural	O
information	O
in	O
many	O
fields	O
,	O
including	O
computer	B-Application
vision	I-Application
and	O
pattern	O
recognition	O
,	O
and	O
graph	B-General_Concept
matching	I-General_Concept
is	O
an	O
important	O
tool	O
in	O
these	O
areas	O
.	O
</s>
<s>
The	O
case	O
of	O
exact	O
graph	B-General_Concept
matching	I-General_Concept
is	O
known	O
as	O
the	O
graph	O
isomorphism	O
problem	O
.	O
</s>
<s>
Inexact	B-General_Concept
graph	I-General_Concept
matching	I-General_Concept
refers	O
to	O
matching	O
problems	O
when	O
exact	O
matching	O
is	O
impossible	O
,	O
e.g.	O
,	O
when	O
the	O
number	O
of	O
vertices	O
in	O
the	O
two	O
graphs	O
are	O
different	O
.	O
</s>
<s>
For	O
example	O
,	O
in	O
image	O
recognition	O
applications	O
,	O
the	O
results	O
of	O
image	B-Algorithm
segmentation	I-Algorithm
in	O
image	B-Algorithm
processing	I-Algorithm
typically	O
produces	O
data	O
graphs	O
with	O
the	O
numbers	O
of	O
vertices	O
much	O
larger	O
than	O
in	O
the	O
model	O
graphs	O
data	O
expected	O
to	O
match	O
against	O
.	O
</s>
<s>
In	O
the	O
case	O
of	O
attributed	B-Application
graphs	I-Application
,	O
even	O
if	O
the	O
numbers	O
of	O
vertices	O
and	O
edges	O
are	O
the	O
same	O
,	O
the	O
matching	O
still	O
may	O
be	O
only	O
inexact	O
.	O
</s>
<s>
Two	O
categories	O
of	O
search	O
methods	O
are	O
the	O
ones	O
based	O
on	O
identification	O
of	O
possible	O
and	O
impossible	O
pairings	O
of	O
vertices	O
between	O
the	O
two	O
graphs	O
and	O
methods	O
that	O
formulate	O
graph	B-General_Concept
matching	I-General_Concept
as	O
an	O
optimization	O
problem	O
.	O
</s>
<s>
Graph	O
edit	O
distance	O
is	O
one	O
of	O
similarity	O
measures	O
suggested	O
for	O
graph	B-General_Concept
matching	I-General_Concept
.	O
</s>
<s>
The	O
class	O
of	O
algorithms	O
is	O
called	O
error-tolerant	O
graph	B-General_Concept
matching	I-General_Concept
.	O
</s>
