<s>
A	O
program	B-Data_Structure
structure	I-Data_Structure
tree	I-Data_Structure
(	O
PST	O
)	O
is	O
a	O
hierarchical	O
diagram	O
that	O
displays	O
the	O
nesting	B-General_Concept
relationship	O
of	O
single-entry	O
single-exit	O
(	O
SESE	O
)	O
fragments/regions	O
,	O
showing	O
the	O
organization	O
of	O
a	O
computer	B-Application
program	I-Application
.	O
</s>
<s>
Nodes	O
in	O
this	O
tree	O
represent	O
SESE	O
regions	O
of	O
the	O
program	O
,	O
while	O
edges	O
represent	O
nesting	B-General_Concept
regions	O
.	O
</s>
<s>
(	O
1994	O
)	O
proposed	O
a	O
program	B-Data_Structure
structure	I-Data_Structure
tree	I-Data_Structure
(	O
PST	O
)	O
,	O
a	O
hierarchical	O
representation	O
of	O
program	O
structure	O
based	O
on	O
single	O
edge	O
entry	O
and	O
single	O
edge	O
exit	O
regions	O
.	O
</s>
