<s>
In	O
computer	B-General_Concept
science	I-General_Concept
,	O
the	O
abstract	B-Application
syntax	I-Application
of	O
data	O
is	O
its	O
structure	O
described	O
as	O
a	O
data	O
type	O
(	O
possibly	O
,	O
but	O
not	O
necessarily	O
,	O
an	O
abstract	O
data	O
type	O
)	O
,	O
independent	O
of	O
any	O
particular	O
representation	O
or	O
encoding	O
.	O
</s>
<s>
This	O
is	O
particularly	O
used	O
in	O
the	O
representation	O
of	O
text	O
in	O
computer	B-Language
languages	I-Language
,	O
which	O
are	O
generally	O
stored	O
in	O
a	O
tree	O
structure	O
as	O
an	O
abstract	B-Data_Structure
syntax	I-Data_Structure
tree	I-Data_Structure
.	O
</s>
<s>
Abstract	B-Application
syntax	I-Application
,	O
which	O
only	O
consists	O
of	O
the	O
structure	O
of	O
data	O
,	O
is	O
contrasted	O
with	O
concrete	O
syntax	O
,	O
which	O
also	O
includes	O
information	O
about	O
the	O
representation	O
.	O
</s>
<s>
For	O
example	O
,	O
concrete	O
syntax	O
includes	O
features	O
like	O
parentheses	O
(	O
for	O
grouping	O
)	O
or	O
commas	O
(	O
for	O
lists	O
)	O
which	O
are	O
not	O
included	O
in	O
the	O
abstract	B-Application
syntax	I-Application
,	O
as	O
they	O
are	O
implicit	O
in	O
the	O
structure	O
.	O
</s>
<s>
Abstract	B-Application
syntaxes	I-Application
are	O
classified	O
as	O
first-order	B-Application
abstract	I-Application
syntax	I-Application
(	O
FOAS	O
)	O
,	O
if	O
the	O
structure	O
is	O
abstract	O
but	O
names	O
(	O
identifiers	O
)	O
are	O
still	O
concrete	O
(	O
and	O
thus	O
requires	O
name	B-Application
resolution	I-Application
)	O
,	O
and	O
higher-order	B-Application
abstract	I-Application
syntax	I-Application
,	O
if	O
the	O
names	O
themselves	O
are	O
abstract	O
.	O
</s>
<s>
To	O
be	O
implemented	O
either	O
for	O
computation	O
or	O
communications	O
,	O
a	O
mapping	O
from	O
the	O
abstract	B-Application
syntax	I-Application
to	O
specific	O
machine	O
representations	O
and	O
encodings	O
must	O
be	O
defined	O
;	O
these	O
may	O
be	O
called	O
the	O
"	O
concrete	O
syntax	O
"	O
(	O
in	O
language	O
implementation	O
)	O
or	O
the	O
"	O
transfer	O
syntax	O
"	O
(	O
in	O
communications	O
)	O
.	O
</s>
<s>
A	O
compiler	B-Language
's	O
internal	O
representation	O
of	O
a	O
program	O
will	O
typically	O
be	O
specified	O
by	O
an	O
abstract	B-Application
syntax	I-Application
in	O
terms	O
of	O
categories	O
such	O
as	O
"	O
statement	O
"	O
,	O
"	O
expression	O
"	O
and	O
"	O
identifier	O
"	O
.	O
</s>
<s>
This	O
is	O
independent	O
of	O
the	O
source	O
syntax	O
(	O
concrete	O
syntax	O
)	O
of	O
the	O
language	O
being	O
compiled	B-Language
(	O
though	O
it	O
will	O
often	O
be	O
very	O
similar	O
)	O
.	O
</s>
<s>
A	O
parse	O
tree	O
is	O
similar	O
to	O
an	O
abstract	B-Data_Structure
syntax	I-Data_Structure
tree	I-Data_Structure
but	O
it	O
will	O
typically	O
also	O
contain	O
features	O
such	O
as	O
parentheses	O
which	O
are	O
syntactically	O
significant	O
but	O
which	O
are	O
implicit	O
in	O
the	O
structure	O
of	O
the	O
abstract	B-Data_Structure
syntax	I-Data_Structure
tree	I-Data_Structure
.	O
</s>
<s>
Algebraic	O
data	O
types	O
are	O
particularly	O
well-suited	O
to	O
the	O
implementation	O
of	O
abstract	B-Application
syntax	I-Application
.	O
</s>
