<s>
The	O
network	B-General_Concept
model	I-General_Concept
is	O
a	O
database	B-General_Concept
model	I-General_Concept
conceived	O
as	O
a	O
flexible	O
way	O
of	O
representing	O
objects	O
and	O
their	O
relationships	O
.	O
</s>
<s>
The	O
network	B-General_Concept
model	I-General_Concept
was	O
adopted	O
by	O
the	O
CODASYL	B-Language
Data	B-Language
Base	I-Language
Task	I-Language
Group	I-Language
in	O
1969	O
and	O
underwent	O
a	O
major	O
update	O
in	O
1971	O
.	O
</s>
<s>
It	O
is	O
sometimes	O
known	O
as	O
the	O
CODASYL	B-Language
model	O
for	O
this	O
reason	O
.	O
</s>
<s>
A	O
number	O
of	O
network	B-General_Concept
database	I-General_Concept
systems	O
became	O
popular	O
on	O
mainframe	B-Architecture
and	O
minicomputers	B-Architecture
through	O
the	O
1970s	O
before	O
being	O
widely	O
replaced	O
by	O
relational	B-Application
databases	I-Application
in	O
the	O
1980s	O
.	O
</s>
<s>
While	O
the	O
hierarchical	B-General_Concept
database	I-General_Concept
model	I-General_Concept
structures	O
data	O
as	O
a	O
tree	B-Application
of	O
records	O
,	O
with	O
each	O
record	O
having	O
one	O
parent	O
record	O
and	O
many	O
children	O
,	O
the	O
network	B-General_Concept
model	I-General_Concept
allows	O
each	O
record	O
to	O
have	O
multiple	O
parent	O
and	O
child	O
records	O
,	O
forming	O
a	O
generalized	O
graph	O
structure	O
.	O
</s>
<s>
This	O
property	O
applies	O
at	O
two	O
levels	O
:	O
the	O
schema	O
is	O
a	O
generalized	O
graph	O
of	O
record	O
types	O
connected	O
by	O
relationship	O
types	O
(	O
called	O
"	O
set	O
types	O
"	O
in	O
CODASYL	B-Language
)	O
,	O
and	O
the	O
database	O
itself	O
is	O
a	O
generalized	O
graph	O
of	O
record	O
occurrences	O
connected	O
by	O
relationships	O
(	O
CODASYL	B-Language
"	O
sets	O
"	O
)	O
.	O
</s>
<s>
The	O
chief	O
argument	O
in	O
favour	O
of	O
the	O
network	B-General_Concept
model	I-General_Concept
,	O
in	O
comparison	O
to	O
the	O
hierarchical	B-General_Concept
model	I-General_Concept
,	O
was	O
that	O
it	O
allowed	O
a	O
more	O
natural	O
modeling	O
of	O
relationships	O
between	O
entities	O
.	O
</s>
<s>
Firstly	O
,	O
IBM	O
chose	O
to	O
stick	O
to	O
the	O
hierarchical	B-General_Concept
model	I-General_Concept
with	O
semi-network	O
extensions	O
in	O
their	O
established	O
products	O
such	O
as	O
IMS	B-Application
and	O
DL/I	O
.	O
</s>
<s>
Secondly	O
,	O
it	O
was	O
eventually	O
displaced	O
by	O
the	O
relational	B-Architecture
model	I-Architecture
,	O
which	O
offered	O
a	O
higher-level	O
,	O
more	O
declarative	O
interface	O
.	O
</s>
<s>
Until	O
the	O
early	O
1980s	O
the	O
performance	O
benefits	O
of	O
the	O
low-level	O
navigational	O
interfaces	O
offered	O
by	O
hierarchical	O
and	O
network	B-General_Concept
databases	I-General_Concept
were	O
persuasive	O
for	O
many	O
large-scale	O
applications	O
,	O
but	O
as	O
hardware	O
became	O
faster	O
,	O
the	O
extra	O
productivity	O
and	O
flexibility	O
of	O
the	O
relational	B-Architecture
model	I-Architecture
led	O
to	O
the	O
gradual	O
obsolescence	O
of	O
the	O
network	B-General_Concept
model	I-General_Concept
in	O
corporate	O
enterprise	O
usage	O
.	O
</s>
<s>
The	O
network	B-General_Concept
model	I-General_Concept
's	O
original	O
inventor	O
was	O
Charles	O
Bachman	O
,	O
and	O
it	O
was	O
developed	O
into	O
a	O
standard	O
specification	O
published	O
in	O
1969	O
by	O
the	O
Conference	B-Language
on	I-Language
Data	I-Language
Systems	I-Language
Languages	I-Language
(	O
CODASYL	B-Language
)	O
Consortium	O
.	O
</s>
<s>
Bachman	O
's	O
influence	O
is	O
recognized	O
in	O
the	O
term	O
Bachman	O
diagram	O
,	O
a	O
diagrammatic	O
notation	O
that	O
represents	O
a	O
database	O
schema	O
expressed	O
using	O
the	O
network	B-General_Concept
model	I-General_Concept
.	O
</s>
<s>
In	O
a	O
Bachman	O
diagram	O
,	O
named	O
rectangles	O
represent	O
record	O
types	O
,	O
and	O
arrows	O
represent	O
one-to-many	O
relationship	O
types	O
between	O
records	O
(	O
CODASYL	B-Language
set	O
types	O
)	O
.	O
</s>
<s>
Some	O
well-known	O
database	O
systems	O
that	O
use	O
the	O
network	B-General_Concept
model	I-General_Concept
include	O
:	O
</s>
