<s>
VME	O
(	O
Virtual	O
Machine	O
Environment	O
)	O
is	O
a	O
mainframe	B-Architecture
operating	B-General_Concept
system	I-General_Concept
developed	O
by	O
the	O
UK	O
company	O
International	O
Computers	O
Limited	O
(	O
ICL	O
,	O
now	O
part	O
of	O
the	O
Fujitsu	O
group	O
)	O
.	O
</s>
<s>
Originally	O
developed	O
in	O
the	O
1970s	O
(	O
as	O
VME/B	O
,	O
later	O
VME	O
2900	O
)	O
to	O
drive	O
ICL	O
's	O
then	O
new	O
2900	B-Device
Series	I-Device
mainframes	B-Architecture
,	O
the	O
operating	B-General_Concept
system	I-General_Concept
is	O
now	O
known	O
as	O
OpenVME	O
incorporating	O
a	O
Unix	B-Application
subsystem	O
,	O
and	O
runs	O
on	O
ICL	B-Device
Series	I-Device
39	I-Device
and	O
Trimetra	O
mainframe	B-Architecture
computers	I-Architecture
,	O
as	O
well	O
as	O
industry-standard	O
x64	B-Device
servers	O
.	O
</s>
<s>
The	O
development	O
program	O
for	O
the	O
New	B-Device
Range	I-Device
system	O
started	O
on	O
the	O
merger	O
of	O
International	O
Computers	O
and	O
Tabulators	O
(	O
ICT	O
)	O
and	O
English	B-Device
Electric	I-Device
Computers	I-Device
in	O
1968	O
.	O
</s>
<s>
One	O
of	O
the	O
fundamental	O
decisions	O
was	O
that	O
it	O
would	O
feature	O
a	O
new	O
operating	B-General_Concept
system	I-General_Concept
.	O
</s>
<s>
The	O
chief	O
architect	O
of	O
VME/B	O
was	O
Brian	O
Warboys	O
,	O
who	O
subsequently	O
became	O
professor	O
of	O
software	B-General_Concept
engineering	I-General_Concept
at	O
the	O
University	O
of	O
Manchester	O
.	O
</s>
<s>
A	O
number	O
of	O
influences	O
can	O
be	O
seen	O
in	O
its	O
design	O
,	O
for	O
example	O
Multics	B-Application
and	O
ICL	O
's	O
earlier	O
George	B-General_Concept
3	I-General_Concept
operating	B-General_Concept
system	I-General_Concept
;	O
however	O
it	O
was	O
essentially	O
designed	O
from	O
scratch	O
.	O
</s>
<s>
VME/B	O
was	O
viewed	O
as	O
primarily	O
competing	O
with	O
the	O
System/370	B-Device
IBM	B-Device
mainframe	I-Device
as	O
a	O
commercial	O
operating	B-General_Concept
system	I-General_Concept
,	O
and	O
adopted	O
the	O
EBCDIC	B-Language
character	B-General_Concept
encoding	I-General_Concept
.	O
</s>
<s>
When	O
New	B-Device
Range	I-Device
was	O
first	O
launched	O
in	O
October	O
1974	O
,	O
its	O
operating	B-General_Concept
system	I-General_Concept
was	O
referred	O
to	O
as	O
"	O
System	O
B	O
"	O
.	O
</s>
<s>
VME/K	O
was	O
developed	O
independently	O
(	O
according	O
to	O
Campbell-Kelly	O
,	O
"	O
on	O
a	O
whim	O
of	O
Ed	O
Mack	O
"	O
)	O
,	O
and	O
was	O
delivered	O
later	O
with	O
the	O
smaller	O
mainframes	B-Architecture
such	O
as	O
the	O
2960	O
.	O
</s>
<s>
The	O
"	O
2900	O
"	O
suffix	O
was	O
dropped	O
at	O
System	O
Version	O
213	O
(	O
SV213	O
)	O
when	O
ICL	O
launched	O
Series	B-Device
39	I-Device
in	O
1985	O
as	O
the	O
successor	O
to	O
the	O
original	O
2900	B-Device
series	I-Device
;	O
and	O
the	O
"	O
Open	O
"	O
prefix	O
was	O
added	O
after	O
SV294	O
.	O
</s>
<s>
VME	O
became	O
capable	O
of	O
hosting	O
applications	O
written	O
originally	O
for	O
Unix	B-Application
through	O
a	O
UNIX	B-Operating_System
System	I-Operating_System
V	I-Operating_System
Release	I-Operating_System
3	I-Operating_System
based	O
subsystem	O
,	O
called	O
VME/X	O
,	O
adapted	O
to	O
run	O
under	O
VME	O
and	O
using	O
the	O
ASCII	B-Protocol
character	I-Protocol
encoding	I-Protocol
.	O
</s>
<s>
In	O
2007	O
Fujitsu	O
announced	O
a	O
VME	O
version	O
run	O
as	O
a	O
hosted	O
subsystem	O
,	O
called	O
superNova	O
,	O
within	O
Microsoft	B-Application
Windows	I-Application
,	O
or	O
SUSE	O
or	O
Red	O
Hat	O
Enterprise	O
Linux	O
on	O
x86-64	B-Device
hardware	O
.	O
</s>
<s>
The	O
concept	O
is	O
similar	O
to	O
the	O
"	O
rings	O
of	O
protection	O
"	O
in	O
Multics	B-Application
.	O
</s>
<s>
Orthogonally	O
to	O
the	O
access	O
levels	O
,	O
the	O
operating	B-General_Concept
system	I-General_Concept
makes	O
resources	O
available	O
to	O
applications	O
in	O
the	O
form	O
of	O
a	O
Virtual	O
Machine	O
.	O
</s>
<s>
In	O
practice	O
,	O
a	O
VME	O
Virtual	O
Machine	O
is	O
closer	O
to	O
the	O
concept	O
of	O
a	O
process	O
on	O
other	O
operating	B-General_Concept
systems	I-General_Concept
,	O
while	O
a	O
VME	O
process	O
is	O
more	O
like	O
a	O
thread	O
.	O
</s>
<s>
Calls	O
from	O
an	O
application	O
to	O
the	O
operating	B-General_Concept
system	I-General_Concept
are	O
therefore	O
made	O
by	O
a	O
call	O
that	O
retains	O
the	O
same	O
process	O
stack	O
,	O
but	O
with	O
a	O
change	O
in	O
protection	O
level	O
;	O
the	O
resulting	O
efficiency	O
of	O
system	O
calls	O
is	O
one	O
of	O
the	O
features	O
that	O
makes	O
the	O
architecture	O
competitive	O
.	O
</s>
<s>
The	O
hardware	O
architecture	O
also	O
provides	O
semaphore	B-Operating_System
instructions	O
INCT	O
(	O
increment-and-test	O
)	O
and	O
TDEC	O
(	O
test-and-decrement	O
)	O
.	O
</s>
<s>
Files	O
and	O
other	O
persistent	O
objects	O
are	O
recorded	O
in	O
a	O
repository	B-Application
called	O
the	O
Catalogue	O
.	O
</s>
<s>
Unlike	O
other	O
operating	B-General_Concept
systems	I-General_Concept
,	O
the	O
file	O
naming	O
hierarchy	O
is	O
independent	O
of	O
the	O
location	O
of	O
a	O
file	O
on	O
a	O
particular	O
tape	O
or	O
disk	O
volume	O
.	O
</s>
<s>
The	O
Catalogue	O
was	O
probably	O
the	O
first	O
example	O
of	O
what	O
would	O
later	O
be	O
called	O
an	O
entity-relationship	B-Architecture
database	O
.	O
</s>
<s>
Interrupts	B-Application
are	O
handled	O
by	O
creating	O
a	O
new	O
stack	O
frame	O
on	O
the	O
stack	O
for	O
the	O
relevant	O
process	O
,	O
handling	O
the	O
interrupt	B-Application
using	O
this	O
new	O
environment	O
,	O
and	O
then	O
popping	O
the	O
stack	O
to	O
return	O
to	O
the	O
interrupted	O
process	O
.	O
</s>
<s>
Run-time	O
exceptions	O
,	O
referred	O
to	O
as	O
contingencies	O
,	O
are	O
captured	O
by	O
the	O
Object	O
Program	O
Error	O
Handler	O
(	O
OPEH	O
)	O
,	O
which	O
can	O
produce	O
a	O
report	O
(	O
equivalent	O
to	O
a	O
stack	B-Language
trace	I-Language
)	O
,	O
either	O
interactively	O
or	O
written	O
to	O
a	O
journal	O
.	O
</s>
<s>
Unlike	O
in	O
many	O
other	O
operating	B-General_Concept
systems	I-General_Concept
,	O
this	O
is	O
also	O
the	O
format	O
used	O
by	O
the	O
loader	O
.	O
</s>
<s>
Various	O
compilers	O
are	O
available	O
,	O
as	O
well	O
as	O
utilities	O
,	O
notably	O
the	O
Collector	O
,	O
which	O
links	O
the	O
code	O
in	O
several	O
OMF	O
modules	O
into	O
a	O
single	O
module	O
,	O
for	O
more	O
efficient	O
loading	O
at	O
run-time	O
,	O
and	O
the	O
Module	O
Amender	O
,	O
which	O
allows	O
patching	O
of	O
the	O
instructions	O
in	O
an	O
OMF	O
module	O
to	O
fix	O
bugs	O
,	O
using	O
assembly	B-Language
language	I-Language
syntax	O
.	O
</s>
<s>
This	O
is	O
much	O
more	O
recognizably	O
a	O
typed	O
high-level	B-Language
programming	I-Language
language	I-Language
than	O
the	O
job	O
control	O
or	O
shell	O
languages	O
found	O
in	O
most	O
other	O
operating	B-General_Concept
systems	I-General_Concept
:	O
it	O
can	O
be	O
likened	O
to	O
scripting	O
languages	O
such	O
as	O
JavaScript	B-Language
,	O
though	O
its	O
surface	O
syntax	O
is	O
derived	O
from	O
Algol	B-Language
68	I-Language
.	O
</s>
<s>
SCL	O
is	O
designed	O
to	O
allow	O
both	O
line-at-a-time	O
interactive	O
use	O
from	O
a	O
console	O
or	O
from	O
a	O
command	B-Language
file	I-Language
,	O
and	O
creation	O
of	O
executable	O
scripts	O
or	O
programs	O
(	O
when	O
the	O
language	O
is	O
compiled	O
into	O
object	O
module	O
format	O
in	O
the	O
same	O
way	O
as	O
any	O
other	O
VME	O
programming	O
language	O
)	O
.	O
</s>
<s>
SCL	O
is	O
block-structured	O
,	O
with	O
begin/end	O
blocks	O
serving	O
the	O
dual	O
and	O
complementary	O
roles	O
of	O
defining	O
the	O
lexical	O
scope	O
of	O
variable	O
declarations	O
,	O
and	O
defining	O
the	O
points	O
at	O
which	O
resources	O
acquired	O
from	O
the	O
operating	B-General_Concept
system	I-General_Concept
should	O
be	O
released	O
.	O
</s>
<s>
A	O
more	O
realistic	O
example	O
,	O
where	O
SCL	O
is	O
used	O
to	O
compile	O
a	O
program	O
written	O
in	O
S3	B-Language
,	O
is	O
shown	O
below	O
.	O
</s>
<s>
This	O
example	O
is	O
taken	O
from	O
the	O
Columbia	O
University	O
Archive	O
of	O
implementations	O
of	O
Kermit	B-Protocol
.	O
</s>
<s>
Commands	O
illustrated	O
in	O
this	O
fragment	O
include	O
WHENEVER	O
(	O
declares	O
error	O
handling	O
policy	O
)	O
,	O
ASSIGN_LIBRARY	O
(	O
binds	O
a	O
local	O
name	O
for	O
a	O
file	O
directory	O
)	O
,	O
DELETE_FILE	O
(	O
Makes	O
a	O
permanent	O
file	O
temporary	O
,	O
and	O
it	O
is	O
then	O
deleted	O
at	O
the	O
END	O
of	O
the	O
block	O
)	O
,	O
S3_COMPILE	O
(	O
compiles	O
a	O
program	O
written	O
in	O
S3	B-Language
:	O
this	O
command	O
breaks	O
the	O
usual	O
verb-noun	O
convention	O
)	O
,	O
NEW_MESSAGE_TEXT_MODULE	O
(	O
creates	O
a	O
module	O
containing	O
parameterized	O
error	O
messages	O
suitable	O
for	O
localization	O
)	O
and	O
COMPILE_SCL	O
,	O
which	O
compiles	O
an	O
SCL	O
program	O
into	O
object	O
code	O
.	O
</s>
<s>
The	O
COLLECT	O
command	O
combines	O
different	O
object	O
code	O
modules	O
into	O
a	O
single	O
module	O
,	O
and	O
is	O
driven	O
by	O
its	O
own	O
local	O
command	B-Language
file	I-Language
which	O
is	O
incorporated	O
inline	O
in	O
the	O
SCL	O
between	O
the	O
delimiters	O
"	O
----	O
"	O
and	O
"	O
++++	O
"	O
.	O
</s>
<s>
The	O
operating	B-General_Concept
system	I-General_Concept
associates	O
a	O
generation	O
number	O
with	O
every	O
file	O
,	O
and	O
requests	O
for	O
a	O
file	O
get	O
the	O
latest	O
generation	O
unless	O
specified	O
otherwise	O
.	O
</s>
<s>
It	O
had	O
the	O
advantage	O
that	O
as	O
the	O
last	O
large-scale	O
operating	B-General_Concept
system	I-General_Concept
ever	O
designed	O
,	O
and	O
one	O
built	O
from	O
scratch	O
,	O
its	O
underlying	O
architecture	O
encompassed	O
many	O
of	O
the	O
primitives	O
needed	O
to	O
develop	O
a	O
Secure	O
System	O
,	O
in	O
particular	O
the	O
hardware	O
assisted	O
Access	O
Control	O
Registers	O
(	O
ACR	O
)	O
to	O
limit	O
to	O
privileges	O
that	O
could	O
be	O
taken	O
by	O
any	O
process	O
(	O
including	O
Users	O
)	O
.	O
</s>
<s>
HSO	O
and	O
GSO	O
were	O
formally	O
tested	O
under	O
the	O
CESG	O
UK	O
(	O
Security	O
)	O
Evaluation	O
Scheme	O
,	O
one	O
of	O
the	O
predecessors	O
to	O
ITSEC	O
and	O
Common	O
Criteria	O
,	O
and	O
in	O
doing	O
so	O
became	O
the	O
first	O
mainstream	O
operating	B-General_Concept
system	I-General_Concept
to	O
be	O
formally	O
Certified	O
.	O
</s>
<s>
The	O
Series	B-Device
39	I-Device
range	O
introduced	O
Nodal	B-Device
Architecture	I-Device
,	O
a	O
novel	O
implementation	O
of	O
distributed	B-Operating_System
shared	I-Operating_System
memory	I-Operating_System
that	O
can	O
be	O
seen	O
as	O
a	O
hybrid	O
of	O
a	O
multiprocessor	B-Operating_System
system	O
and	O
a	O
cluster	B-Architecture
design	O
.	O
</s>
<s>
Each	O
machine	O
consists	O
of	O
a	O
number	O
of	O
nodes	B-Protocol
,	O
and	O
each	O
node	O
contains	O
its	O
own	O
order-code	O
processor	O
(	O
CPU	O
)	O
and	O
main	O
memory	O
.	O
</s>
<s>
Discs	O
and	O
other	O
peripherals	O
are	O
shared	O
between	O
nodes	B-Protocol
.	O
</s>
<s>
Nodes	B-Protocol
are	O
connected	O
using	O
a	O
high-speed	O
optical	O
bus	O
,	O
which	O
is	O
used	O
to	O
provide	O
applications	O
with	O
a	O
virtual	O
shared	O
memory	O
.	O
</s>
<s>
Processes	O
which	O
use	O
unshared	O
memory	O
segments	O
(	O
nodal	O
or	O
local	O
)	O
run	O
in	O
complete	O
isolation	O
from	O
other	O
nodes	B-Protocol
and	O
processes	O
.	O
</s>
<s>
VME	O
was	O
originally	O
written	O
almost	O
entirely	O
in	O
S3	B-Language
,	O
a	O
specially-designed	O
system	B-Language
programming	I-Language
language	I-Language
based	O
on	O
Algol	B-General_Concept
68R	I-General_Concept
(	O
however	O
,	O
VME/K	O
was	O
written	O
primarily	O
in	O
the	O
SFL	B-Language
assembly	B-Language
language	I-Language
)	O
.	O
</s>
<s>
Although	O
a	O
high-level	B-Language
language	I-Language
is	O
used	O
,	O
the	O
operating	B-General_Concept
system	I-General_Concept
is	O
not	O
designed	O
to	O
be	O
independent	O
of	O
the	O
underlying	O
hardware	O
architecture	O
:	O
on	O
the	O
contrary	O
,	O
the	O
software	O
and	O
hardware	O
architecture	O
are	O
closely	O
integrated	O
.	O
</s>
<s>
From	O
the	O
early	O
1990s	O
onwards	O
,	O
some	O
entirely	O
new	O
VME	O
subsystems	O
were	O
written	O
partly	O
or	O
wholly	O
in	O
the	O
C	B-Language
programming	I-Language
language	I-Language
.	O
</s>
<s>
From	O
its	O
earliest	O
days	O
,	O
VME	O
was	O
developed	O
with	O
the	O
aid	O
of	O
a	O
software	B-General_Concept
engineering	I-General_Concept
repository	B-Application
system	I-Application
known	O
as	O
CADES	O
,	O
originally	O
designed	O
and	O
managed	O
by	O
David	O
Pearson	O
(	O
computer	O
scientist	O
)	O
and	O
built	O
for	O
the	O
purpose	O
using	O
an	O
underlying	O
IDMS	B-Application
database	O
.	O
</s>
<s>
CADES	O
is	O
not	O
merely	O
a	O
version	B-Architecture
control	I-Architecture
system	I-Architecture
for	O
code	O
modules	O
:	O
it	O
manages	O
all	O
aspects	O
of	O
the	O
software	O
lifecycle	O
from	O
requirements	O
capture	O
,	O
design	O
methodology	O
and	O
specification	O
through	O
to	O
field	O
maintenance	O
.	O
</s>
<s>
The	O
algorithms	O
were	O
written	O
in	O
System	O
Development	O
Language	O
(	O
SDL	O
)	O
,	O
which	O
was	O
then	O
converted	O
to	O
S3	B-Language
source	O
by	O
a	O
pre-processor	O
.	O
</s>
<s>
fourth-generation	B-Language
QuickBuild	O
toolset	O
.	O
</s>
<s>
For	O
many	O
years	O
the	O
large	O
majority	O
of	O
VME	O
users	O
wrote	O
applications	O
in	O
COBOL	B-Application
,	O
usually	O
making	O
use	O
of	O
the	O
IDMS	B-Application
database	O
and	O
the	O
TPMS	O
transaction	B-General_Concept
processing	I-General_Concept
monitor	I-General_Concept
.	O
</s>
<s>
Other	O
programming	O
languages	O
included	O
Fortran	B-Application
,	O
Pascal	B-Application
,	O
ALGOL	B-General_Concept
68RS	I-General_Concept
,	O
Coral	B-Language
66	I-Language
and	O
RPG2	B-Language
,	O
but	O
these	O
served	O
minority	O
interests	O
.	O
</s>
<s>
Later	O
,	O
in	O
the	O
mid	O
1980s	O
,	O
compilers	O
for	O
C	B-Language
became	O
available	O
,	O
both	O
within	O
and	O
outside	O
the	O
Unix	B-Application
subsystem	O
,	O
largely	O
to	O
enable	O
porting	O
of	O
software	O
such	O
as	O
relational	B-Application
database	I-Application
systems	O
.	O
</s>
<s>
It	O
is	O
interesting	O
that	O
a	O
PL/I	B-Language
subset	O
compiler	O
was	O
written	O
by	O
the	O
EEC	O
,	O
to	O
assist	O
in	O
porting	O
programs	O
from	O
IBM	O
to	O
ICL	O
hardware	O
.	O
</s>
<s>
Many	O
of	O
the	O
compilers	O
used	O
a	O
module	O
named	O
ALICE	O
[	O
Assembly	B-Language
Language	I-Language
Internal	O
Common	O
Environment ]	O
and	O
produced	O
an	O
early	O
form	O
of	O
precompiled	O
code	O
(	O
P-Code	O
)	O
termed	O
ROSE	O
,	O
making	O
compiled	O
Object	O
Module	O
Format	O
(	O
OMF	O
)	O
libraries	O
loadable	O
on	O
any	O
machine	O
in	O
the	O
range	O
.	O
</s>
<s>
The	O
primary	O
language	O
used	O
for	O
developing	O
both	O
the	O
VME	O
operating	B-General_Concept
system	I-General_Concept
itself	O
and	O
other	O
system	O
software	O
such	O
as	O
compilers	O
and	O
transaction	B-General_Concept
processing	I-General_Concept
monitors	I-General_Concept
is	O
S3	B-Language
.	O
</s>
<s>
This	O
is	O
a	O
high	B-Language
level	I-Language
language	I-Language
based	O
in	O
many	O
ways	O
on	O
Algol	B-Language
68	I-Language
,	O
but	O
with	O
data	O
types	O
and	O
low-level	O
functions	O
and	O
operators	O
aligned	O
closely	O
with	O
the	O
architecture	O
of	O
the	O
2900	B-Device
series	I-Device
.	O
</s>
<s>
An	O
assembly	B-Language
language	I-Language
SFL	B-Language
(	O
System	O
Function	O
Language	O
)	O
is	O
also	O
available	O
.	O
</s>
<s>
This	O
was	O
used	O
for	O
the	O
development	O
of	O
VME/K	O
,	O
whose	O
designers	O
were	O
not	O
confident	O
that	O
a	O
high-level	B-Language
language	I-Language
could	O
give	O
adequate	O
performance	O
,	O
and	O
also	O
for	O
the	O
IDMS	B-Application
database	O
system	O
on	O
account	O
of	O
its	O
origins	O
as	O
a	O
third-party	O
product	O
.	O
</s>
<s>
SFL	B-Language
was	O
originally	O
called	O
Macro	O
Assembler	B-Language
Programming	I-Language
LanguagE	O
(	O
MAPLE	O
)	O
,	O
but	O
as	O
the	O
2900	O
architecture	O
was	O
being	O
positioned	O
as	O
consisting	O
of	O
high	B-Language
level	I-Language
language	I-Language
machines	O
the	O
name	O
was	O
changed	O
at	O
the	O
request	O
of	O
ICL	O
Marketing	O
.	O
</s>
<s>
Related	O
families	O
of	O
assemblers	B-Language
for	O
other	O
architectures	O
(	O
CALM-xx	O
running	O
under	O
VME	O
,	O
PALM-xx	O
developed	O
in	O
Pascal	B-Application
and	O
running	O
on	O
various	O
hosts	O
)	O
were	O
developed	O
for	O
internal	O
use	O
.	O
</s>
<s>
Neither	O
S3	B-Language
nor	O
SFL	B-Language
was	O
ever	O
promoted	O
as	O
a	O
commercial	O
development	O
tool	O
for	O
end-user	O
applications	O
,	O
as	O
neither	O
were	O
normally	O
delivered	O
as	O
a	O
standard	O
part	O
of	O
the	O
operating	B-General_Concept
system	I-General_Concept
,	O
nor	O
were	O
they	O
explicitly	O
marketed	O
as	O
products	O
in	O
their	O
own	O
right	O
.	O
</s>
<s>
Both	O
SFL	B-Language
and	O
S3	B-Language
were	O
however	O
available	O
as	O
options	O
to	O
user	O
organisations	O
and	O
third	O
parties	O
who	O
had	O
a	O
specific	O
need	O
for	O
them	O
.	O
</s>
<s>
This	O
environment	O
is	O
centred	O
on	O
the	O
Data	O
Dictionary	O
System	O
(	O
DDS	O
,	O
also	O
called	O
OpenDDS	O
)	O
,	O
an	O
early	O
and	O
very	O
successful	O
attempt	O
to	O
build	O
a	O
comprehensive	O
repository	B-Application
supporting	O
all	O
the	O
other	O
tools	O
,	O
with	O
full	O
support	O
for	O
the	O
development	O
lifecycle	O
.	O
</s>
<s>
As	O
well	O
as	O
database	O
schemas	O
and	O
file	O
and	O
record	O
descriptions	O
,	O
the	O
dictionary	O
keeps	O
track	O
of	O
objects	O
such	O
as	O
reports	O
and	O
queries	O
,	O
screen	O
designs	O
,	O
and	O
4GL	B-Language
code	O
;	O
it	O
also	O
supports	O
a	O
variety	O
of	O
models	O
at	O
the	O
requirements	O
capture	O
level	O
,	O
such	O
as	O
entity-relationship	B-Architecture
models	I-Architecture
and	O
process	O
models	O
.	O
</s>
<s>
The	O
QuickBuild	O
4GL	B-Language
is	O
packaged	O
in	O
two	O
forms	O
:	O
</s>
<s>
Both	O
are	O
high-level	O
declarative	O
languages	O
,	O
using	O
Jackson	B-Application
Structured	I-Application
Programming	I-Application
as	O
their	O
design	O
paradigm	O
.	O
</s>
<s>
Because	O
the	O
4GL	B-Language
and	O
other	O
tools	O
such	O
as	O
the	O
screen	O
designer	O
work	O
only	O
with	O
the	O
DDS	O
dictionary	O
,	O
which	O
also	O
holds	O
the	O
database	O
schemas	O
,	O
there	O
is	O
considerable	O
reuse	O
of	O
metadata	O
that	O
is	O
rarely	O
achieved	O
with	O
other	O
4GLs	B-Language
.	O
</s>
