<s>
A	O
navigational	B-General_Concept
database	I-General_Concept
is	O
a	O
type	O
of	O
database	O
in	O
which	O
records	O
or	O
objects	O
are	O
found	O
primarily	O
by	O
following	O
references	O
from	O
other	O
objects	O
.	O
</s>
<s>
One	O
of	O
the	O
earliest	O
navigational	B-General_Concept
databases	I-General_Concept
was	O
Integrated	B-Application
Data	I-Application
Store	I-Application
(	O
IDS	O
)	O
,	O
which	O
was	O
developed	O
by	O
Bachman	O
for	O
General	O
Electric	O
in	O
the	O
1960s	O
.	O
</s>
<s>
IDS	O
became	O
the	O
basis	O
for	O
the	O
CODASYL	B-Language
database	O
model	O
in	O
1969	O
.	O
</s>
<s>
Although	O
Bachman	O
described	O
the	O
concept	O
of	O
navigation	O
in	O
abstract	O
terms	O
,	O
the	O
idea	O
of	O
navigational	O
access	O
came	O
to	O
be	O
associated	O
strongly	O
with	O
the	O
procedural	B-Application
design	O
of	O
the	O
CODASYL	B-Language
Data	B-Language
Manipulation	I-Language
Language	I-Language
.	O
</s>
<s>
Navigational	B-General_Concept
database	I-General_Concept
programming	O
thus	O
came	O
to	O
be	O
seen	O
as	O
intrinsically	O
procedural	B-Application
;	O
and	O
moreover	O
to	O
depend	O
on	O
the	O
maintenance	O
of	O
an	O
implicit	O
set	O
of	O
global	O
variables	O
(	O
currency	O
indicators	O
)	O
holding	O
the	O
current	O
state	O
.	O
</s>
<s>
As	O
such	O
,	O
the	O
approach	O
was	O
seen	O
as	O
diametrically	O
opposed	O
to	O
the	O
declarative	B-Language
programming	I-Language
style	O
used	O
by	O
the	O
relational	B-Architecture
model	I-Architecture
.	O
</s>
<s>
The	O
declarative	B-Language
nature	O
of	O
relational	O
languages	O
such	O
as	O
SQL	B-Language
offered	O
better	O
programmer	O
productivity	O
and	O
a	O
higher	O
level	O
of	O
data	O
independence	O
(	O
that	O
is	O
,	O
the	O
ability	O
of	O
programs	O
to	O
continue	O
working	O
as	O
the	O
database	O
structure	O
evolves	O
.	O
)	O
</s>
<s>
Navigational	O
interfaces	O
,	O
as	O
a	O
result	O
,	O
were	O
gradually	O
eclipsed	O
during	O
the	O
1980s	O
by	O
declarative	B-Language
query	O
languages	O
.	O
</s>
<s>
At	O
that	O
time	O
,	O
a	O
reappraisal	O
of	O
the	O
entire	O
database	O
market	O
began	O
,	O
with	O
several	O
companies	O
describing	O
the	O
new	O
systems	O
using	O
the	O
marketing	O
term	O
NoSQL	B-General_Concept
.	O
</s>
<s>
Many	O
of	O
these	O
systems	O
introduced	O
data	B-Language
manipulation	I-Language
languages	I-Language
which	O
,	O
while	O
far	O
removed	O
from	O
the	O
CODASYL	B-Language
DML	O
with	O
its	O
currency	O
indicators	O
,	O
could	O
be	O
understood	O
as	O
implementing	O
Bachman	O
's	O
"	O
navigational	O
"	O
vision	O
.	O
</s>
<s>
Some	O
of	O
these	O
languages	O
are	O
procedural	B-Application
;	O
others	O
(	O
such	O
as	O
XPath	B-Language
)	O
are	O
entirely	O
declarative	B-Language
.	O
</s>
<s>
Offshoots	O
of	O
the	O
navigational	O
concept	O
,	O
such	O
as	O
the	O
graph	B-Application
database	I-Application
,	O
found	O
new	O
uses	O
in	O
modern	O
transaction	B-General_Concept
processing	I-General_Concept
workloads	O
.	O
</s>
<s>
Navigational	O
access	O
is	O
traditionally	O
associated	O
with	O
the	O
network	B-General_Concept
model	I-General_Concept
and	O
hierarchical	B-General_Concept
model	I-General_Concept
of	O
database	O
,	O
and	O
conventionally	O
describes	O
data	O
manipulation	O
APIs	O
in	O
which	O
records	O
(	O
or	O
objects	O
)	O
are	O
processed	O
one	O
at	O
a	O
time	O
,	O
iteratively	O
.	O
</s>
<s>
From	O
this	O
viewpoint	O
,	O
the	O
key	O
difference	O
between	O
navigational	O
data	B-Language
manipulation	I-Language
languages	I-Language
and	O
relational	O
languages	O
is	O
the	O
use	O
of	O
explicit	O
named	O
relationships	O
rather	O
than	O
value-based	O
joins	O
:	O
for	O
department	O
with	O
name	O
=	O
"	O
Sales	O
"	O
,	O
find	O
all	O
employees	O
in	O
set	O
department-employees	O
versus	O
find	O
employees	O
,	O
departments	O
where	O
employee.department-code	O
=	O
department.code	O
and	O
department.name="Sales	O
"	O
.	O
</s>
<s>
In	O
practice	O
,	O
however	O
,	O
most	O
navigational	O
APIs	O
have	O
been	O
procedural	B-Application
:	O
the	O
above	O
query	O
would	O
be	O
executed	O
using	O
procedural	B-Application
logic	O
along	O
the	O
lines	O
of	O
the	O
following	O
pseudo-code	O
:	O
</s>
<s>
On	O
this	O
viewpoint	O
,	O
the	O
key	O
difference	O
between	O
navigational	O
APIs	O
and	O
the	O
relational	B-Architecture
model	I-Architecture
(	O
implemented	O
in	O
relational	B-Application
databases	I-Application
)	O
is	O
that	O
relational	O
APIs	O
use	O
"	O
declarative	B-Language
"	O
or	O
logic	B-Language
programming	I-Language
techniques	O
that	O
ask	O
the	O
system	O
what	O
to	O
fetch	O
,	O
while	O
navigational	O
APIs	O
instruct	O
the	O
system	O
in	O
a	O
sequence	O
of	O
steps	O
how	O
to	O
reach	O
the	O
required	O
records	O
.	O
</s>
<s>
Hierarchical	B-General_Concept
models	I-General_Concept
often	O
construct	O
primary	O
keys	O
for	O
records	O
by	O
concatenating	O
the	O
keys	O
that	O
appear	O
at	O
each	O
level	O
in	O
the	O
hierarchy	O
.	O
</s>
<s>
As	O
relational	O
systems	O
came	O
to	O
prominence	O
in	O
the	O
1980s	O
,	O
navigational	O
APIs	O
(	O
and	O
in	O
particular	O
,	O
procedural	B-Application
APIs	O
)	O
were	O
criticized	O
and	O
fell	O
out	O
of	O
favour	O
.	O
</s>
<s>
The	O
1990s	O
,	O
however	O
,	O
brought	O
a	O
new	O
wave	O
of	O
object-oriented	B-Application
databases	I-Application
that	O
often	O
provided	O
both	O
declarative	B-Language
and	O
procedural	B-Application
interfaces	O
.	O
</s>
<s>
One	O
explanation	O
for	O
this	O
is	O
that	O
they	O
were	O
often	O
used	O
to	O
represent	O
graph-structured	O
information	O
(	O
for	O
example	O
spatial	O
data	O
and	O
engineering	O
data	O
)	O
where	O
access	O
is	O
inherently	O
recursive	O
:	O
the	O
mathematics	O
underpinning	O
SQL	B-Language
(	O
specifically	O
,	O
first-order	O
predicate	O
calculus	O
)	O
does	O
not	O
have	O
sufficient	O
power	O
to	O
support	O
recursive	O
queries	O
,	O
even	O
those	O
as	O
simple	O
as	O
a	O
transitive	O
closure	O
.	O
</s>
<s>
A	O
current	O
example	O
of	O
a	O
popular	O
navigational	O
API	O
can	O
be	O
found	O
in	O
the	O
Document	B-General_Concept
Object	I-General_Concept
Model	I-General_Concept
(	O
DOM	B-General_Concept
)	O
often	O
used	O
in	O
web	O
browsers	O
and	O
closely	O
associated	O
with	O
JavaScript	B-Language
.	O
</s>
<s>
The	B-General_Concept
DOM	I-General_Concept
is	O
essentially	O
an	O
in-memory	O
hierarchical	B-General_Concept
database	I-General_Concept
with	O
an	O
API	O
that	O
is	O
both	O
procedural	B-Application
and	O
navigational	O
.	O
</s>
<s>
By	O
contrast	O
,	O
the	O
same	O
data	O
(	O
XML	B-Protocol
or	O
HTML	B-Language
)	O
can	O
be	O
accessed	O
using	O
XPath	B-Language
,	O
which	O
can	O
be	O
categorized	O
as	O
declarative	B-Language
and	O
navigational	O
:	O
data	O
is	O
accessed	O
by	O
following	O
relationships	O
,	O
but	O
the	O
calling	O
program	O
does	O
not	O
issue	O
a	O
sequence	O
of	O
instructions	O
to	O
be	O
followed	O
in	O
order	O
.	O
</s>
<s>
Languages	O
such	O
as	O
SPARQL	B-Language
used	O
to	O
retrieve	O
Linked	B-Operating_System
Data	I-Operating_System
from	O
the	O
Semantic	O
Web	O
are	O
also	O
simultaneously	O
declarative	B-Language
and	O
navigational	O
.	O
</s>
