<s>
OPeNDAP	B-Application
is	O
an	O
acronym	O
for	O
"	O
Open-source	O
Project	O
for	O
a	O
Network	O
Data	O
Access	O
Protocol	O
,	O
"	O
an	O
endeavor	O
focused	O
on	O
enhancing	O
the	O
retrieval	O
of	O
remote	O
,	O
structured	O
data	O
through	O
a	O
Web-based	O
architecture	O
and	O
a	O
discipline-neutral	O
Data	O
Access	O
Protocol	O
(	O
DAP	O
)	O
.	O
</s>
<s>
Widely	O
used	O
,	O
especially	O
in	O
Earth	O
science	O
,	O
the	O
protocol	O
is	O
layered	O
on	O
HTTP	B-Protocol
,	O
and	O
its	O
current	O
specification	O
is	O
DAP4	O
,	O
though	O
the	O
previous	O
DAP2	O
version	O
remains	O
broadly	O
used	O
.	O
</s>
<s>
Developed	O
and	O
advanced	O
(	O
openly	O
and	O
collaboratively	O
)	O
by	O
the	O
non-profit	O
OPeNDAP	B-Application
,	O
Inc.	O
,	O
DAP	O
is	O
intended	O
to	O
enable	O
remote	O
,	O
selective	O
data-retrieval	O
as	O
an	O
easily	O
invoked	O
Web	O
service	O
.	O
</s>
<s>
OPeNDAP	B-Application
,	O
Inc	O
.	O
also	O
develops	O
and	O
maintains	O
zero-cost	O
(	O
reference	O
)	O
implementations	O
of	O
the	O
DAP	O
protocol	O
in	O
both	O
server-side	O
and	O
client-side	O
software	O
.	O
</s>
<s>
"	O
OPeNDAP	B-Application
"	O
often	O
is	O
used	O
in	O
place	O
of	O
"	O
DAP	O
"	O
to	O
denote	O
the	O
protocol	O
but	O
also	O
may	O
refer	O
to	O
an	O
entire	O
DAP-based	O
data-retrieval	O
architecture	O
.	O
</s>
<s>
Other	O
DAP-centered	O
architectures	O
,	O
such	O
as	O
THREDDS	O
and	O
ERDDAP	O
,	O
the	O
NOAA	O
GEO-IDE	O
UAF	O
ERDDAP	O
exhibit	O
significant	O
interoperability	O
with	O
one	O
another	O
as	O
well	O
as	O
with	O
systems	O
employing	O
OPeNDAP	B-Application
's	O
own	O
(	O
open-source	O
)	O
servers	O
and	O
software	O
.	O
</s>
<s>
A	O
DAP	O
client	O
can	O
be	O
an	O
ordinary	O
browser	O
or	O
even	O
a	O
spreadsheet	O
,	O
though	O
with	O
limited	O
functionality	O
(	O
see	O
OPeNDAP	B-Application
's	O
Web	O
page	O
on	O
)	O
.	O
</s>
<s>
Data-analysis	O
or	O
data-visualization	O
tools	O
(	O
such	O
as	O
MATLAB	B-Language
,	O
IDL	B-Language
,	O
Panoply	O
,	O
GrADS	B-Application
,	O
Integrated	B-Application
Data	I-Application
Viewer	I-Application
,	O
Ferret	B-Application
and	O
ncBrowse	O
)	O
which	O
their	O
authors	O
have	O
adapted	O
to	O
enable	O
DAP-based	O
data	O
input	O
;	O
</s>
<s>
OPeNDAP	B-Application
offers	O
open-source	O
libraries	O
in	O
C++	B-Language
and	O
Java	B-Language
,	O
but	O
many	O
clients	O
rely	O
on	O
community	O
developed	O
libraries	O
such	O
as	O
or	O
,	O
especially	O
,	O
the	O
NetCDF	B-Application
suite	O
.	O
</s>
<s>
Developed	O
and	O
maintained	O
by	O
the	O
Unidata	O
Program	O
at	O
the	O
UCAR	O
in	O
multiple	O
programming	O
languages	O
,	O
all	O
NetCDF	B-Application
libraries	O
include	O
embedded	O
capabilities	O
for	O
retrieving	O
(	O
array-style	O
)	O
data	O
from	O
DAP	O
servers	O
.	O
</s>
<s>
A	O
data-using	O
client	O
references	O
a	O
data	B-General_Concept
set	I-General_Concept
by	O
its	O
URL	O
and	O
requests	O
metadata	O
or	O
content	O
by	O
issuing	O
(	O
usually	O
through	O
an	O
embedded	O
DAP	O
library	O
)	O
an	O
HTTP	B-Protocol
request	O
to	O
a	O
DAP	O
server	O
.	O
</s>
<s>
Content	O
requests	O
usually	O
are	O
preceded	O
by	O
requests	O
for	O
metadata	O
describing	O
the	O
structure	O
and	O
other	O
details	O
about	O
the	O
referenced	O
data	B-General_Concept
set	I-General_Concept
.	O
</s>
<s>
OPeNDAP	B-Application
servers	O
offer	O
various	O
types	O
of	O
responses	O
,	O
depending	O
on	O
the	O
specific	O
form	O
of	O
the	O
client	O
's	O
request	O
,	O
including	O
XML	O
,	O
JSON	O
,	O
HTML	O
and	O
ASCII	O
.	O
</s>
<s>
In	O
response	O
to	O
requests	O
for	O
content	O
,	O
OPeNDAP	B-Application
servers	O
can	O
respond	O
with	O
multi-part	O
mime	O
documents	O
that	O
include	O
a	O
binary	O
portion	O
with	O
NetCDF	B-Application
or	O
DAP-native	O
encoding	O
.	O
</s>
<s>
OPeNDAP	B-Application
's	O
software	O
for	O
building	O
DAP	O
servers	O
(	O
on	O
top	O
of	O
Apache	B-Application
)	O
is	O
dubbed	O
Hyrax	O
and	O
includes	O
adapters	O
that	O
facilitate	O
serving	O
a	O
wide	O
variety	O
of	O
source	O
data	O
.	O
</s>
<s>
DAP	O
servers	O
most	O
frequently	O
enable	O
(	O
remote	O
)	O
access	O
to	O
(	O
large	O
)	O
HDF	B-Application
or	O
NetCDF	B-Application
files	O
,	O
but	O
the	O
source	O
data	O
can	O
exist	O
in	O
databases	O
or	O
other	O
formats	O
,	O
including	O
user-defined	O
ones	O
.	O
</s>
<s>
When	O
source	O
data	O
are	O
organized	O
as	O
files	O
,	O
DAP	O
retrievals	O
enable	O
,	O
via	O
subsetting	O
,	O
finer-grained	O
access	O
than	O
does	O
the	O
FTP	B-Protocol
.	O
</s>
<s>
Furthermore	O
,	O
OPeNDAP	B-Application
servers	O
can	O
aggregate	O
subsets	O
from	O
multiple	O
files	O
for	O
delivery	O
in	O
a	O
single	O
retrieval	O
.	O
</s>
<s>
OPeNDAP	B-Application
and	O
other	O
DAP	O
servers	O
are	O
used	O
operationally	O
in	O
government	O
agencies	O
,	O
including	O
NASA	O
and	O
NOAA	O
,	O
for	O
providing	O
access	O
to	O
Earth	O
science	O
data	O
,	O
including	O
satellite	O
imagery	O
and	O
other	O
high-volume	O
information	O
sources	O
.	O
</s>
<s>
The	O
DAP	O
data	O
model	O
embraces	O
a	O
comprehensive	O
set	B-General_Concept
of	I-General_Concept
data	I-General_Concept
structures	O
,	O
including	O
multidimensional	O
arrays	O
and	O
nested	O
sequences	O
(	O
i.e.	O
,	O
records	O
)	O
,	O
complemented	O
by	O
a	O
correspondingly	O
rich	O
set	O
of	O
constraint	O
expressions	O
.	O
</s>
<s>
Hence	O
the	O
OPeNDAP	B-Application
data-retrieval	O
architecture	O
has	O
demonstrated	O
utility	O
across	O
a	O
broad	O
range	O
of	O
scientific	O
data	O
types	O
,	O
including	O
data	O
generated	O
via	O
simulations	O
and	O
data	O
generated	O
via	O
observations	O
(	O
whether	O
remotely	O
sensed	O
or	O
measured	O
in	O
situ	O
)	O
.	O
</s>
