<s>
In	O
software	B-General_Concept
engineering	I-General_Concept
,	O
version	B-Architecture
control	I-Architecture
(	O
also	O
known	O
as	O
revision	B-Architecture
control	I-Architecture
,	O
source	B-Architecture
control	I-Architecture
,	O
or	O
source	B-Architecture
code	I-Architecture
management	I-Architecture
)	O
is	O
a	O
class	O
of	O
systems	O
responsible	O
for	O
managing	O
changes	O
to	O
computer	B-Application
programs	I-Application
,	O
documents	O
,	O
large	O
web	O
sites	O
,	O
or	O
other	O
collections	O
of	O
information	O
.	O
</s>
<s>
Version	B-Architecture
control	I-Architecture
is	O
a	O
component	O
of	O
software	O
configuration	B-General_Concept
management	I-General_Concept
.	O
</s>
<s>
Changes	O
are	O
usually	O
identified	O
by	O
a	O
number	O
or	O
letter	O
code	O
,	O
termed	O
the	O
"	O
revision	B-Architecture
number	I-Architecture
"	O
,	O
"	O
revision	B-Architecture
level	I-Architecture
"	O
,	O
or	O
simply	O
"	O
revision	O
"	O
.	O
</s>
<s>
The	O
need	O
for	O
a	O
logical	O
way	O
to	O
organize	O
and	O
control	O
revisions	O
has	O
existed	O
for	O
almost	O
as	O
long	O
as	O
writing	O
has	O
existed	O
,	O
but	O
revision	B-Architecture
control	I-Architecture
became	O
much	O
more	O
important	O
,	O
and	O
complicated	O
,	O
when	O
the	O
era	O
of	O
computing	O
began	O
.	O
</s>
<s>
Today	O
,	O
the	O
most	O
capable	O
(	O
as	O
well	O
as	O
complex	O
)	O
revision	B-Architecture
control	I-Architecture
systems	I-Architecture
are	O
those	O
used	O
in	O
software	O
development	O
,	O
where	O
a	O
team	O
of	O
people	O
may	O
concurrently	O
make	O
changes	O
to	O
the	O
same	O
files	O
.	O
</s>
<s>
Version	B-Architecture
control	I-Architecture
systems	I-Architecture
are	O
most	O
commonly	O
run	O
as	O
stand-alone	O
applications	O
,	O
but	O
revision	B-Architecture
control	I-Architecture
is	O
also	O
embedded	O
in	O
various	O
types	O
of	O
software	O
,	O
such	O
as	O
word	B-General_Concept
processors	I-General_Concept
and	O
spreadsheets	B-Application
,	O
collaborative	O
web	B-Application
docs	I-Application
,	O
and	O
content	B-Protocol
management	I-Protocol
systems	I-Protocol
,	O
e.g.	O
,	O
Wikipedia	O
's	O
page	O
history	O
.	O
</s>
<s>
Revision	B-Architecture
control	I-Architecture
enables	O
reverting	O
a	O
document	O
to	O
a	O
previous	O
revision	O
,	O
which	O
is	O
critical	O
for	O
allowing	O
editors	O
to	O
track	O
each	O
other	O
's	O
edits	O
,	O
correct	O
mistakes	O
,	O
and	O
defend	O
against	O
vandalism	O
and	O
spamming	O
in	O
wikis	B-Protocol
.	O
</s>
<s>
In	O
computer	B-General_Concept
software	I-General_Concept
engineering	I-General_Concept
,	O
revision	B-Architecture
control	I-Architecture
is	O
any	O
kind	O
of	O
practice	O
that	O
tracks	O
and	O
provides	O
control	O
over	O
changes	O
to	O
source	O
code	O
.	O
</s>
<s>
Software	B-Application
developers	I-Application
sometimes	O
use	O
revision	B-Architecture
control	I-Architecture
software	I-Architecture
to	O
maintain	O
documentation	O
and	O
configuration	B-Protocol
files	I-Protocol
as	O
well	O
as	O
source	O
code	O
.	O
</s>
<s>
As	O
teams	O
design	O
,	O
develop	O
and	O
deploy	O
software	O
,	O
it	O
is	O
common	O
for	O
multiple	O
versions	O
of	O
the	O
same	O
software	O
to	O
be	O
deployed	O
in	O
different	O
sites	O
and	O
for	O
the	O
software	O
's	O
developers	B-Application
to	O
be	O
working	O
simultaneously	O
on	O
updates	O
.	O
</s>
<s>
Bugs	B-Error_Name
or	O
features	O
of	O
the	O
software	O
are	O
often	O
only	O
present	O
in	O
certain	O
versions	O
(	O
because	O
of	O
the	O
fixing	O
of	O
some	O
problems	O
and	O
the	O
introduction	O
of	O
others	O
as	O
the	O
program	O
develops	O
)	O
.	O
</s>
<s>
Therefore	O
,	O
for	O
the	O
purposes	O
of	O
locating	O
and	O
fixing	O
bugs	B-Error_Name
,	O
it	O
is	O
vitally	O
important	O
to	O
be	O
able	O
to	O
retrieve	O
and	O
run	O
different	O
versions	O
of	O
the	O
software	O
to	O
determine	O
in	O
which	O
version(s )	O
the	O
problem	O
occurs	O
.	O
</s>
<s>
It	O
may	O
also	O
be	O
necessary	O
to	O
develop	O
two	O
versions	O
of	O
the	O
software	O
concurrently	O
:	O
for	O
instance	O
,	O
where	O
one	O
version	O
has	O
bugs	B-Error_Name
fixed	O
,	O
but	O
no	O
new	O
features	O
(	O
branch	B-General_Concept
)	O
,	O
while	O
the	O
other	O
version	O
is	O
where	O
new	O
features	O
are	O
worked	O
on	O
(	O
trunk	B-General_Concept
)	O
.	O
</s>
<s>
At	O
the	O
simplest	O
level	O
,	O
developers	B-Application
could	O
simply	O
retain	O
multiple	O
copies	O
of	O
the	O
different	O
versions	O
of	O
the	O
program	O
,	O
and	O
label	O
them	O
appropriately	O
.	O
</s>
<s>
This	O
requires	O
a	O
lot	O
of	O
self-discipline	O
on	O
the	O
part	O
of	O
developers	B-Application
and	O
often	O
leads	O
to	O
mistakes	O
.	O
</s>
<s>
Since	O
the	O
code	O
base	O
is	O
the	O
same	O
,	O
it	O
also	O
requires	O
granting	O
read-write-execute	O
permission	O
to	O
a	O
set	O
of	O
developers	B-Application
,	O
and	O
this	O
adds	O
the	O
pressure	O
of	O
someone	O
managing	O
permissions	O
so	O
that	O
the	O
code	O
base	O
is	O
not	O
compromised	O
,	O
which	O
adds	O
more	O
complexity	O
.	O
</s>
<s>
Consequently	O
,	O
systems	O
to	O
automate	O
some	O
or	O
all	O
of	O
the	O
revision	B-Architecture
control	I-Architecture
process	O
have	O
been	O
developed	O
.	O
</s>
<s>
This	O
ensures	O
that	O
the	O
majority	O
of	O
management	O
of	O
version	B-Architecture
control	I-Architecture
steps	O
is	O
hidden	O
behind	O
the	O
scenes	O
.	O
</s>
<s>
Sophisticated	O
revision	B-Architecture
control	I-Architecture
that	O
tracks	O
and	O
accounts	O
for	O
ownership	O
of	O
changes	O
to	O
documents	O
and	O
code	O
may	O
be	O
extremely	O
helpful	O
or	O
even	O
indispensable	O
in	O
such	O
situations	O
.	O
</s>
<s>
Revision	B-Architecture
control	I-Architecture
may	O
also	O
track	O
changes	O
to	O
configuration	B-Protocol
files	I-Protocol
,	O
such	O
as	O
those	O
typically	O
stored	O
in	O
/etc	O
or	O
/usr/local/etc	O
on	O
Unix	O
systems	O
.	O
</s>
<s>
IBM	O
's	O
OS/360	O
IEBUPDTE	O
software	O
update	O
tool	O
dates	O
back	O
to	O
1962	O
,	O
arguably	O
a	O
precursor	O
to	O
version	B-Architecture
control	I-Architecture
system	I-Architecture
tools	O
.	O
</s>
<s>
A	O
full	O
system	O
designed	O
for	O
source	O
code	O
control	O
was	O
started	O
in	O
1972	O
,	O
Source	B-Device
Code	I-Device
Control	I-Device
System	I-Device
for	O
the	O
same	O
system	O
(	O
OS/360	O
)	O
.	O
</s>
<s>
Source	B-Device
Code	I-Device
Control	I-Device
System	I-Device
's	O
introduction	O
,	O
having	O
been	O
published	O
on	O
December	O
4	O
,	O
1975	O
,	O
historically	O
implied	O
it	O
was	O
the	O
first	O
deliberate	O
revision	B-Architecture
control	I-Architecture
system	I-Architecture
.	O
</s>
<s>
RCS	B-Architecture
followed	O
just	O
after	O
,	O
with	O
its	O
networked	O
version	O
Concurrent	B-Application
Versions	I-Application
System	I-Application
.	O
</s>
<s>
The	O
next	O
generation	O
after	O
Concurrent	B-Application
Versions	I-Application
System	I-Application
was	O
dominated	O
by	O
Subversion	B-Application
,	O
followed	O
by	O
the	O
rise	O
of	O
distributed	B-Protocol
revision	I-Protocol
control	I-Protocol
tools	O
such	O
as	O
Git	B-Application
.	O
</s>
<s>
Revision	B-Architecture
control	I-Architecture
manages	O
changes	O
to	O
a	O
set	O
of	O
data	O
over	O
time	O
.	O
</s>
<s>
Accordingly	O
,	O
some	O
systems	O
such	O
as	O
Git	B-Application
,	O
instead	O
consider	O
changes	O
to	O
the	O
data	O
as	O
a	O
whole	O
,	O
which	O
is	O
less	O
intuitive	O
for	O
simple	O
changes	O
but	O
simplifies	O
more	O
complex	O
changes	O
.	O
</s>
<s>
When	O
data	O
that	O
is	O
under	O
revision	B-Architecture
control	I-Architecture
is	O
modified	O
,	O
after	O
being	O
retrieved	O
by	O
checking	O
out	O
,	O
this	O
is	O
not	O
in	O
general	O
immediately	O
reflected	O
in	O
the	O
revision	B-Architecture
control	I-Architecture
system	I-Architecture
(	O
in	O
the	O
repository	B-General_Concept
)	O
,	O
but	O
must	O
instead	O
be	O
checked	O
in	O
or	O
committed	O
.	O
</s>
<s>
A	O
copy	O
outside	O
revision	B-Architecture
control	I-Architecture
is	O
known	O
as	O
a	O
"	O
working	O
copy	O
"	O
.	O
</s>
<s>
For	O
source	O
code	O
control	O
,	O
the	O
working	O
copy	O
is	O
instead	O
a	O
copy	O
of	O
all	O
files	O
in	O
a	O
particular	O
revision	O
,	O
generally	O
stored	O
locally	O
on	O
the	O
developer	B-Application
's	O
computer	O
;	O
in	O
this	O
case	O
saving	O
the	O
file	O
only	O
changes	O
the	O
working	O
copy	O
,	O
and	O
checking	O
into	O
the	O
repository	B-General_Concept
is	O
a	O
separate	O
step	O
.	O
</s>
<s>
For	O
simple	O
collaborative	O
document	O
editing	O
,	O
this	O
can	O
be	O
prevented	O
by	O
using	O
file	B-Application
locking	I-Application
or	O
simply	O
avoiding	O
working	O
on	O
the	O
same	O
document	O
that	O
someone	O
else	O
is	O
working	O
on	O
.	O
</s>
<s>
Revision	B-Architecture
control	I-Architecture
systems	I-Architecture
are	O
often	O
centralized	O
,	O
with	O
a	O
single	O
authoritative	O
data	O
store	O
,	O
the	O
repository	B-General_Concept
,	O
and	O
check-outs	O
and	O
check-ins	O
done	O
with	O
reference	O
to	O
this	O
central	O
repository	B-General_Concept
.	O
</s>
<s>
Alternatively	O
,	O
in	O
distributed	B-Protocol
revision	I-Protocol
control	I-Protocol
,	O
no	O
single	O
repository	B-General_Concept
is	O
authoritative	O
,	O
and	O
data	O
can	O
be	O
checked	O
out	O
and	O
checked	O
into	O
any	O
repository	B-General_Concept
.	O
</s>
<s>
When	O
checking	O
into	O
a	O
different	O
repository	B-General_Concept
,	O
this	O
is	O
interpreted	O
as	O
a	O
merge	B-General_Concept
or	O
patch	B-Application
.	O
</s>
<s>
In	O
terms	O
of	O
graph	O
theory	O
,	O
revisions	O
are	O
generally	O
thought	O
of	O
as	O
a	O
line	O
of	O
development	O
(	O
the	O
trunk	B-General_Concept
)	O
with	O
branches	O
off	O
of	O
this	O
,	O
forming	O
a	O
directed	O
tree	O
,	O
visualized	O
as	O
one	O
or	O
more	O
parallel	O
lines	O
of	O
development	O
(	O
the	O
"	O
mainlines	B-General_Concept
"	O
of	O
the	O
branches	O
)	O
branching	B-General_Concept
off	O
a	O
trunk	B-General_Concept
.	O
</s>
<s>
In	O
reality	O
the	O
structure	O
is	O
more	O
complicated	O
,	O
forming	O
a	O
directed	O
acyclic	O
graph	O
,	O
but	O
for	O
many	O
purposes	O
"	O
tree	O
with	O
merges	B-General_Concept
"	O
is	O
an	O
adequate	O
approximation	O
.	O
</s>
<s>
Revisions	O
occur	O
in	O
sequence	O
over	O
time	O
,	O
and	O
thus	O
can	O
be	O
arranged	O
in	O
order	O
,	O
either	O
by	O
revision	B-Architecture
number	I-Architecture
or	O
timestamp	O
.	O
</s>
<s>
In	O
the	O
simplest	O
case	O
,	O
with	O
no	O
branching	B-General_Concept
or	O
undoing	O
,	O
each	O
revision	O
is	O
based	O
on	O
its	O
immediate	O
predecessor	O
alone	O
,	O
and	O
they	O
form	O
a	O
simple	O
line	O
,	O
with	O
a	O
single	O
latest	O
version	O
,	O
the	O
"	O
HEAD	O
"	O
revision	O
or	O
tip	O
.	O
</s>
<s>
If	O
there	O
is	O
branching	B-General_Concept
,	O
so	O
multiple	O
future	O
revisions	O
are	O
based	O
on	O
a	O
past	O
revision	O
,	O
or	O
undoing	O
,	O
so	O
a	O
revision	O
can	O
depend	O
on	O
a	O
revision	O
older	O
than	O
its	O
immediate	O
predecessor	O
,	O
then	O
the	O
resulting	O
graph	O
is	O
instead	O
a	O
directed	O
tree	O
(	O
each	O
node	O
can	O
have	O
more	O
than	O
one	O
child	O
)	O
,	O
and	O
has	O
multiple	O
tips	O
,	O
corresponding	O
to	O
the	O
revisions	O
without	O
children	O
(	O
"	O
latest	O
revision	O
on	O
each	O
branch	B-General_Concept
"	O
)	O
.	O
</s>
<s>
When	O
a	O
new	O
revision	O
is	O
based	O
on	O
HEAD	O
,	O
it	O
is	O
either	O
identified	O
as	O
the	O
new	O
HEAD	O
,	O
or	O
considered	O
a	O
new	O
branch	B-General_Concept
.	O
</s>
<s>
The	O
list	O
of	O
revisions	O
from	O
the	O
start	O
to	O
HEAD	O
(	O
in	O
graph	O
theory	O
terms	O
,	O
the	O
unique	O
path	O
in	O
the	O
tree	O
,	O
which	O
forms	O
a	O
linear	O
graph	O
as	O
before	O
)	O
is	O
the	O
trunk	B-General_Concept
or	O
mainline	B-General_Concept
.	O
</s>
<s>
Conversely	O
,	O
when	O
a	O
revision	O
can	O
be	O
based	O
on	O
more	O
than	O
one	O
previous	O
revision	O
(	O
when	O
a	O
node	O
can	O
have	O
more	O
than	O
one	O
parent	O
)	O
,	O
the	O
resulting	O
process	O
is	O
called	O
a	O
merge	B-General_Concept
,	O
and	O
is	O
one	O
of	O
the	O
most	O
complex	O
aspects	O
of	O
revision	B-Architecture
control	I-Architecture
.	O
</s>
<s>
This	O
most	O
often	O
occurs	O
when	O
changes	O
occur	O
in	O
multiple	O
branches	O
(	O
most	O
often	O
two	O
,	O
but	O
more	O
are	O
possible	O
)	O
,	O
which	O
are	O
then	O
merged	O
into	O
a	O
single	O
branch	B-General_Concept
incorporating	O
both	O
changes	O
.	O
</s>
<s>
If	O
these	O
changes	O
overlap	O
,	O
it	O
may	O
be	O
difficult	O
or	O
impossible	O
to	O
merge	B-General_Concept
,	O
and	O
require	O
manual	O
intervention	O
or	O
rewriting	O
.	O
</s>
<s>
In	O
the	O
presence	O
of	O
merges	B-General_Concept
,	O
the	O
resulting	O
graph	O
is	O
no	O
longer	O
a	O
tree	O
,	O
as	O
nodes	O
can	O
have	O
multiple	O
parents	O
,	O
but	O
is	O
instead	O
a	O
rooted	O
directed	O
acyclic	O
graph	O
(	O
DAG	O
)	O
.	O
</s>
<s>
Assuming	O
there	O
is	O
a	O
trunk	B-General_Concept
,	O
merges	B-General_Concept
from	O
branches	O
can	O
be	O
considered	O
as	O
"	O
external	O
"	O
to	O
the	O
tree	O
–	O
the	O
changes	O
in	O
the	O
branch	B-General_Concept
are	O
packaged	O
up	O
as	O
a	O
patch	B-Application
,	O
which	O
is	O
applied	O
to	O
HEAD	O
(	O
of	O
the	O
trunk	B-General_Concept
)	O
,	O
creating	O
a	O
new	O
revision	O
without	O
any	O
explicit	O
reference	O
to	O
the	O
branch	B-General_Concept
,	O
and	O
preserving	O
the	O
tree	O
structure	O
.	O
</s>
<s>
Thus	O
,	O
while	O
the	O
actual	O
relations	O
between	O
versions	O
form	O
a	O
DAG	O
,	O
this	O
can	O
be	O
considered	O
a	O
tree	O
plus	O
merges	B-General_Concept
,	O
and	O
the	O
trunk	B-General_Concept
itself	O
is	O
a	O
line	O
.	O
</s>
<s>
In	O
distributed	B-Protocol
revision	I-Protocol
control	I-Protocol
,	O
in	O
the	O
presence	O
of	O
multiple	O
repositories	B-General_Concept
these	O
may	O
be	O
based	O
on	O
a	O
single	O
original	O
version	O
(	O
a	O
root	O
of	O
the	O
tree	O
)	O
,	O
but	O
there	O
need	O
not	O
be	O
an	O
original	O
root	O
,	O
and	O
thus	O
only	O
a	O
separate	O
root	O
(	O
oldest	O
revision	O
)	O
for	O
each	O
repository	B-General_Concept
,	O
for	O
example	O
,	O
if	O
two	O
people	O
starting	O
working	O
on	O
a	O
project	O
separately	O
.	O
</s>
<s>
Similarly	O
in	O
the	O
presence	O
of	O
multiple	O
data	O
sets	O
(	O
multiple	O
projects	O
)	O
that	O
exchange	O
data	O
or	O
merge	B-General_Concept
,	O
there	O
is	O
n't	O
a	O
single	O
root	O
,	O
though	O
for	O
simplicity	O
one	O
may	O
think	O
of	O
one	O
project	O
as	O
primary	O
and	O
the	O
other	O
as	O
secondary	O
,	O
merged	O
into	O
the	O
first	O
with	O
or	O
without	O
its	O
own	O
revision	O
history	O
.	O
</s>
<s>
Engineering	O
revision	B-Architecture
control	I-Architecture
developed	O
from	O
formalized	O
processes	O
based	O
on	O
tracking	O
revisions	O
of	O
early	O
blueprints	O
or	O
bluelines	B-Application
.	O
</s>
<s>
Version	B-Architecture
control	I-Architecture
is	O
widespread	O
in	O
business	O
and	O
law	O
.	O
</s>
<s>
Indeed	O
,	O
"	O
contract	O
redline	O
"	O
and	O
"	O
legal	O
blackline	O
"	O
are	O
some	O
of	O
the	O
earliest	O
forms	O
of	O
revision	B-Architecture
control	I-Architecture
,	O
and	O
are	O
still	O
employed	O
in	O
business	O
and	O
law	O
with	O
varying	O
degrees	O
of	O
sophistication	O
.	O
</s>
<s>
The	O
most	O
sophisticated	O
techniques	O
are	O
beginning	O
to	O
be	O
used	O
for	O
the	O
electronic	O
tracking	O
of	O
changes	O
to	O
CAD	B-Application
files	I-Application
(	O
see	O
product	B-Application
data	I-Application
management	I-Application
)	O
,	O
supplanting	O
the	O
"	O
manual	O
"	O
electronic	O
implementation	O
of	O
traditional	O
revision	B-Architecture
control	I-Architecture
.	O
</s>
<s>
Traditional	O
revision	B-Architecture
control	I-Architecture
systems	I-Architecture
use	O
a	O
centralized	O
model	O
where	O
all	O
the	O
revision	B-Architecture
control	I-Architecture
functions	O
take	O
place	O
on	O
a	O
shared	O
server	B-Application
.	O
</s>
<s>
If	O
two	O
developers	B-Application
try	O
to	O
change	O
the	O
same	O
file	O
at	O
the	O
same	O
time	O
,	O
without	O
some	O
method	O
of	O
managing	O
access	O
the	O
developers	B-Application
may	O
end	O
up	O
overwriting	O
each	O
other	O
's	O
work	O
.	O
</s>
<s>
Centralized	O
revision	B-Architecture
control	I-Architecture
systems	I-Architecture
solve	O
this	O
problem	O
in	O
one	O
of	O
two	O
different	O
"	O
source	O
management	O
models	O
"	O
:	O
file	B-Application
locking	I-Application
and	O
version	O
merging	O
.	O
</s>
<s>
An	O
operation	O
is	O
atomic	B-General_Concept
if	O
the	O
system	O
is	O
left	O
in	O
a	O
consistent	O
state	O
even	O
if	O
the	O
operation	O
is	O
interrupted	O
.	O
</s>
<s>
The	O
commit	B-Protocol
operation	O
is	O
usually	O
the	O
most	O
critical	O
in	O
this	O
sense	O
.	O
</s>
<s>
Commits	O
tell	O
the	O
revision	B-Architecture
control	I-Architecture
system	I-Architecture
to	O
make	O
a	O
group	O
of	O
changes	O
final	O
,	O
and	O
available	O
to	O
all	O
users	O
.	O
</s>
<s>
Not	O
all	O
revision	B-Architecture
control	I-Architecture
systems	I-Architecture
have	O
atomic	B-General_Concept
commits	O
;	O
Concurrent	B-Application
Versions	I-Application
System	I-Application
lacks	O
this	O
feature	O
.	O
</s>
<s>
The	O
simplest	O
method	O
of	O
preventing	O
"	O
concurrent	B-Operating_System
access	I-Operating_System
"	O
problems	O
involves	O
locking	B-Application
files	I-Application
so	O
that	O
only	O
one	O
developer	B-Application
at	O
a	O
time	O
has	O
write	O
access	O
to	O
the	O
central	O
"	O
repository	B-General_Concept
"	O
copies	O
of	O
those	O
files	O
.	O
</s>
<s>
Once	O
one	O
developer	B-Application
"	O
checks	O
out	O
"	O
a	O
file	O
,	O
others	O
can	O
read	O
that	O
file	O
,	O
but	O
no	O
one	O
else	O
may	O
change	O
that	O
file	O
until	O
that	O
developer	B-Application
"	O
checks	O
in	O
"	O
the	O
updated	O
version	O
(	O
or	O
cancels	O
the	O
checkout	O
)	O
.	O
</s>
<s>
File	B-Application
locking	I-Application
has	O
both	O
merits	O
and	O
drawbacks	O
.	O
</s>
<s>
It	O
can	O
provide	O
some	O
protection	O
against	O
difficult	O
merge	B-General_Concept
conflicts	O
when	O
a	O
user	O
is	O
making	O
radical	O
changes	O
to	O
many	O
sections	O
of	O
a	O
large	O
file	O
(	O
or	O
group	O
of	O
files	O
)	O
.	O
</s>
<s>
If	O
the	O
files	O
are	O
left	O
exclusively	O
locked	O
for	O
too	O
long	O
,	O
other	O
developers	B-Application
may	O
be	O
tempted	O
to	O
bypass	O
the	O
revision	B-Architecture
control	I-Architecture
software	I-Architecture
and	O
change	O
the	O
files	O
locally	O
,	O
forcing	O
a	O
difficult	O
manual	O
merge	B-General_Concept
when	O
the	O
other	O
changes	O
are	O
finally	O
checked	O
in	O
.	O
</s>
<s>
In	O
a	O
large	O
organization	O
,	O
files	O
can	O
be	O
left	O
"	O
checked	O
out	O
"	O
and	O
locked	O
and	O
forgotten	O
about	O
as	O
developers	B-Application
move	O
between	O
projects	O
-	O
these	O
tools	O
may	O
or	O
may	O
not	O
make	O
it	O
easy	O
to	O
see	O
who	O
has	O
a	O
file	O
checked	O
out	O
.	O
</s>
<s>
Most	O
version	B-Architecture
control	I-Architecture
systems	I-Architecture
allow	O
multiple	O
developers	B-Application
to	O
edit	O
the	O
same	O
file	O
at	O
the	O
same	O
time	O
.	O
</s>
<s>
The	O
first	O
developer	B-Application
to	O
"	O
check	O
in	O
"	O
changes	O
to	O
the	O
central	O
repository	B-General_Concept
always	O
succeeds	O
.	O
</s>
<s>
The	O
system	O
may	O
provide	O
facilities	O
to	O
merge	B-General_Concept
further	O
changes	O
into	O
the	O
central	O
repository	B-General_Concept
,	O
and	O
preserve	O
the	O
changes	O
from	O
the	O
first	O
developer	B-Application
when	O
other	O
developers	B-Application
check	O
in	O
.	O
</s>
<s>
Merging	O
two	O
files	O
can	O
be	O
a	O
very	O
delicate	O
operation	O
,	O
and	O
usually	O
possible	O
only	O
if	O
the	O
data	O
structure	O
is	O
simple	O
,	O
as	O
in	O
text	B-General_Concept
files	I-General_Concept
.	O
</s>
<s>
The	O
result	O
of	O
a	O
merge	B-General_Concept
of	O
two	O
image	O
files	O
might	O
not	O
result	O
in	O
an	O
image	O
file	O
at	O
all	O
.	O
</s>
<s>
The	O
second	O
developer	B-Application
checking	O
in	O
the	O
code	O
will	O
need	O
to	O
take	O
care	O
with	O
the	O
merge	B-General_Concept
,	O
to	O
make	O
sure	O
that	O
the	O
changes	O
are	O
compatible	O
and	O
that	O
the	O
merge	B-General_Concept
operation	O
does	O
not	O
introduce	O
its	O
own	O
logic	O
errors	O
within	O
the	O
files	O
.	O
</s>
<s>
These	O
problems	O
limit	O
the	O
availability	O
of	O
automatic	O
or	O
semi-automatic	O
merge	B-General_Concept
operations	O
mainly	O
to	O
simple	O
text-based	O
documents	O
,	O
unless	O
a	O
specific	O
merge	B-General_Concept
plugin	B-Application
is	O
available	O
for	O
the	O
file	O
types	O
.	O
</s>
<s>
Most	O
revision	B-Architecture
control	I-Architecture
tools	O
will	O
use	O
only	O
one	O
of	O
these	O
similar	O
terms	O
(	O
baseline	O
,	O
label	O
,	O
tag	B-Protocol
)	O
to	O
refer	O
to	O
the	O
action	O
of	O
identifying	O
a	O
snapshot	O
(	O
"	O
label	O
the	O
project	O
"	O
)	O
or	O
the	O
record	O
of	O
the	O
snapshot	O
(	O
"	O
try	O
it	O
with	O
baseline	O
X	O
"	O
)	O
.	O
</s>
<s>
Typically	O
only	O
one	O
of	O
the	O
terms	O
baseline	O
,	O
label	O
,	O
or	O
tag	B-Protocol
is	O
used	O
in	O
documentation	O
or	O
discussion	O
;	O
they	O
can	O
be	O
considered	O
synonyms	O
.	O
</s>
<s>
When	O
both	O
the	O
term	O
baseline	O
and	O
either	O
of	O
label	O
or	O
tag	B-Protocol
are	O
used	O
together	O
in	O
the	O
same	O
context	O
,	O
label	O
and	O
tag	B-Protocol
usually	O
refer	O
to	O
the	O
mechanism	O
within	O
the	O
tool	O
of	O
identifying	O
or	O
making	O
the	O
record	O
of	O
the	O
snapshot	O
,	O
and	O
baseline	O
indicates	O
the	O
increased	O
significance	O
of	O
any	O
given	O
label	O
or	O
tag	B-Protocol
.	O
</s>
<s>
Most	O
formal	O
discussion	O
of	O
configuration	B-General_Concept
management	I-General_Concept
uses	O
the	O
term	O
baseline	O
.	O
</s>
<s>
Distributed	B-Protocol
revision	I-Protocol
control	I-Protocol
systems	I-Protocol
(	O
DRCS	B-Protocol
)	O
take	O
a	O
peer-to-peer	O
approach	O
,	O
as	O
opposed	O
to	O
the	O
client	B-Operating_System
–	I-Operating_System
server	I-Operating_System
approach	O
of	O
centralized	O
systems	O
.	O
</s>
<s>
Rather	O
than	O
a	O
single	O
,	O
central	O
repository	B-General_Concept
on	O
which	O
clients	O
synchronize	O
,	O
each	O
peer	O
's	O
working	O
copy	O
of	O
the	O
codebase	O
is	O
a	O
bona-fide	O
repository	B-General_Concept
.	O
</s>
<s>
Distributed	B-Protocol
revision	I-Protocol
control	I-Protocol
conducts	O
synchronization	O
by	O
exchanging	O
patches	B-Application
(	O
change-sets	O
)	O
from	O
peer	O
to	O
peer	O
.	O
</s>
<s>
Common	O
operations	O
(	O
such	O
as	O
commits	O
,	O
viewing	O
history	O
,	O
and	O
reverting	O
changes	O
)	O
are	O
fast	O
,	O
because	O
there	O
is	O
no	O
need	O
to	O
communicate	O
with	O
a	O
central	O
server	B-Application
.	O
</s>
<s>
Following	O
best	O
practices	O
is	O
necessary	O
to	O
obtain	O
the	O
full	O
benefits	O
of	O
version	B-Architecture
control	I-Architecture
.	O
</s>
<s>
Best	O
practice	O
may	O
vary	O
by	O
version	B-Architecture
control	I-Architecture
tool	O
and	O
the	O
field	O
to	O
which	O
version	B-Architecture
control	I-Architecture
is	O
applied	O
.	O
</s>
<s>
The	O
generally	O
accepted	O
best	O
practices	O
in	O
software	O
development	O
include	O
:	O
making	O
incremental	O
,	O
small	O
,	O
changes	O
;	O
making	O
commits	O
which	O
involve	O
only	O
one	O
task	O
or	O
fix	O
--	O
a	O
corollary	O
to	O
this	O
is	O
to	O
commit	B-Protocol
only	O
code	O
which	O
works	O
and	O
does	O
not	O
knowingly	O
break	O
existing	O
functionality	O
;	O
utilizing	O
branching	B-General_Concept
to	O
complete	O
functionality	O
before	O
release	O
;	O
writing	O
clear	O
and	O
descriptive	O
commit	B-Protocol
messages	O
,	O
make	O
what	O
why	O
and	O
how	O
clear	O
in	O
either	O
the	O
description	O
or	O
the	O
code	O
;	O
and	O
using	O
a	O
consistent	O
branching	B-General_Concept
strategy	O
.	O
</s>
<s>
Other	O
best	O
software	O
development	O
practices	O
such	O
as	O
code	O
review	O
and	O
automated	O
regression	O
testing	O
may	O
assist	O
in	O
the	O
following	O
of	O
version	B-Architecture
control	I-Architecture
best	O
practices	O
.	O
</s>
<s>
Costs	O
and	O
benefits	O
will	O
vary	O
dependent	O
upon	O
the	O
version	B-Architecture
control	I-Architecture
tool	O
chosen	O
and	O
the	O
field	O
in	O
which	O
it	O
is	O
applied	O
.	O
</s>
<s>
This	O
section	O
speaks	O
to	O
the	O
field	O
of	O
software	O
development	O
,	O
where	O
version	B-Architecture
control	I-Architecture
is	O
widely	O
applied	O
.	O
</s>
<s>
In	O
addition	O
to	O
the	O
costs	O
of	O
licensing	O
the	O
version	B-Architecture
control	I-Architecture
software	I-Architecture
,	O
using	O
version	B-Architecture
control	I-Architecture
requires	O
time	O
and	O
effort	O
.	O
</s>
<s>
The	O
concepts	O
underlying	O
version	B-Architecture
control	I-Architecture
must	O
be	O
understood	O
and	O
the	O
technical	O
particulars	O
required	O
to	O
operate	O
the	O
version	B-Architecture
control	I-Architecture
software	I-Architecture
chosen	O
must	O
be	O
learned	O
.	O
</s>
<s>
Version	B-Architecture
control	I-Architecture
best	O
practices	O
must	O
be	O
learned	O
and	O
integrated	O
into	O
the	O
organization	O
's	O
existing	O
software	O
development	O
practices	O
.	O
</s>
<s>
A	O
core	O
benefit	O
is	O
the	O
ability	O
to	O
keep	O
history	O
and	O
revert	O
changes	O
,	O
allowing	O
the	O
developer	B-Application
to	O
easily	O
undo	O
changes	O
.	O
</s>
<s>
This	O
gives	O
the	O
developer	B-Application
more	O
opportunity	O
to	O
experiment	O
,	O
eliminating	O
the	O
fear	O
of	O
breaking	O
existing	O
code	O
.	O
</s>
<s>
Branching	B-General_Concept
assists	O
with	O
deployment	O
.	O
</s>
<s>
Branching	B-General_Concept
and	O
merging	O
,	O
the	O
production	O
,	O
packaging	O
,	O
and	O
labeling	O
of	O
source	O
code	O
patches	B-Application
and	O
the	O
easy	O
application	O
of	O
patches	B-Application
to	O
code	O
bases	O
,	O
simplifies	O
the	O
maintenance	O
and	O
concurrent	O
development	O
of	O
the	O
multiple	O
code	O
bases	O
associated	O
with	O
the	O
various	O
stages	O
of	O
the	O
deployment	O
process	O
;	O
development	O
,	O
testing	O
,	O
staging	O
,	O
production	O
,	O
etc	O
.	O
</s>
<s>
There	O
can	O
be	O
damage	O
mitigation	O
,	O
accountability	O
,	O
process	O
and	O
design	O
improvement	O
,	O
and	O
other	O
benefits	O
associated	O
with	O
the	O
record	O
keeping	O
provided	O
by	O
version	B-Architecture
control	I-Architecture
,	O
the	O
tracking	O
of	O
who	O
did	O
what	O
,	O
when	O
,	O
why	O
,	O
and	O
how	O
.	O
</s>
<s>
When	O
bugs	B-Error_Name
arise	O
,	O
knowing	O
what	O
was	O
done	O
when	O
helps	O
with	O
damage	O
mitigation	O
and	O
recovery	O
by	O
assisting	O
in	O
the	O
identification	O
of	O
what	O
problems	O
exist	O
,	O
how	O
long	O
they	O
have	O
existed	O
,	O
and	O
determining	O
problem	O
scope	O
and	O
solutions	O
.	O
</s>
<s>
Previous	O
versions	O
can	O
be	O
installed	O
and	O
tested	O
to	O
verify	O
conclusions	O
reached	O
by	O
examination	O
of	O
code	O
and	O
commit	B-Protocol
messages	O
.	O
</s>
<s>
Version	B-Architecture
control	I-Architecture
can	O
greatly	O
simplify	O
debugging	O
.	O
</s>
<s>
The	O
application	O
of	O
a	O
test	O
case	O
to	O
multiple	O
versions	O
can	O
quickly	O
identify	O
the	O
change	O
which	O
introduced	O
a	O
bug	B-Error_Name
.	O
</s>
<s>
The	O
developer	B-Application
need	O
not	O
be	O
familiar	O
with	O
the	O
entire	O
code	O
base	O
and	O
can	O
focus	O
instead	O
on	O
the	O
code	O
that	O
introduced	O
the	O
problem	O
.	O
</s>
<s>
Version	B-Architecture
control	I-Architecture
enhances	O
collaboration	O
in	O
multiple	O
ways	O
.	O
</s>
<s>
Since	O
version	B-Architecture
control	I-Architecture
can	O
identify	O
conflicting	O
changes	O
,	O
i.e.	O
</s>
<s>
incompatible	O
changes	O
made	O
to	O
the	O
same	O
lines	O
of	O
code	O
,	O
there	O
is	O
less	O
need	O
for	O
coordination	O
among	O
developers	B-Application
.	O
</s>
<s>
The	O
packaging	O
of	O
commits	O
,	O
branches	O
,	O
and	O
all	O
the	O
associated	O
commit	B-Protocol
messages	O
and	O
version	O
labels	O
,	O
improves	O
communication	O
between	O
developers	B-Application
,	O
both	O
in	O
the	O
moment	O
and	O
over	O
time	O
.	O
</s>
<s>
Plugins	B-Application
are	O
often	O
available	O
for	O
IDEs	B-Application
such	O
as	O
Oracle	B-Language
JDeveloper	I-Language
,	O
IntelliJ	B-Language
IDEA	I-Language
,	O
Eclipse	B-Application
,	O
Visual	B-Application
Studio	I-Application
,	O
Delphi	B-Language
,	O
NetBeans	B-Application
IDE	I-Application
,	O
Xcode	B-Operating_System
,	O
and	O
GNU	B-Application
Emacs	I-Application
(	O
via	O
vc.el	O
)	O
.	O
</s>
<s>
Advanced	O
research	O
prototypes	O
generate	O
appropriate	O
commit	B-Protocol
messages	O
.	O
</s>
<s>
Branch	B-General_Concept
A	O
set	O
of	O
files	O
under	O
version	B-Architecture
control	I-Architecture
may	O
be	O
branched	O
or	O
forked	O
at	O
a	O
point	O
in	O
time	O
so	O
that	O
,	O
from	O
that	O
time	O
forward	O
,	O
two	O
copies	O
of	O
those	O
files	O
may	O
develop	O
at	O
different	O
speeds	O
or	O
in	O
different	O
ways	O
independently	O
of	O
each	O
other	O
.	O
</s>
<s>
Change	O
A	O
change	O
(	O
or	O
diff	B-Application
,	O
or	O
delta	B-Algorithm
)	O
represents	O
a	O
specific	O
modification	O
to	O
a	O
document	O
under	O
version	B-Architecture
control	I-Architecture
.	O
</s>
<s>
The	O
granularity	O
of	O
the	O
modification	O
considered	O
a	O
change	O
varies	O
between	O
version	B-Architecture
control	I-Architecture
systems	I-Architecture
.	O
</s>
<s>
Change	O
list	O
On	O
many	O
version	B-Architecture
control	I-Architecture
systems	I-Architecture
with	O
atomic	B-General_Concept
multi-change	O
commits	O
,	O
a	O
change	O
list	O
(	O
or	O
CL	O
)	O
,	O
change	O
set	O
,	O
update	O
,	O
or	O
patch	B-Application
identifies	O
the	O
set	O
of	O
changes	O
made	O
in	O
a	O
single	O
commit	B-Protocol
.	O
</s>
<s>
Checkout	O
To	O
check	O
out	O
(	O
or	O
co	O
)	O
is	O
to	O
create	O
a	O
local	O
working	O
copy	O
from	O
the	O
repository	B-General_Concept
.	O
</s>
<s>
When	O
a	O
file	O
has	O
been	O
checked	O
out	O
from	O
a	O
shared	O
file	O
server	B-Application
,	O
it	O
cannot	O
be	O
edited	O
by	O
other	O
users	O
.	O
</s>
<s>
Clone	O
Cloning	O
means	O
creating	O
a	O
repository	B-General_Concept
containing	O
the	O
revisions	O
from	O
another	O
repository	B-General_Concept
.	O
</s>
<s>
This	O
is	O
equivalent	O
to	O
pushing	O
or	O
pulling	O
into	O
an	O
empty	O
(	O
newly	O
initialized	O
)	O
repository	B-General_Concept
.	O
</s>
<s>
As	O
a	O
noun	O
,	O
two	O
repositories	B-General_Concept
can	O
be	O
said	O
to	O
be	O
clones	O
if	O
they	O
are	O
kept	O
synchronized	O
,	O
and	O
contain	O
the	O
same	O
revisions	O
.	O
</s>
<s>
Commit	B-Protocol
(	O
noun	O
)	O
A	O
'	O
commit	B-Protocol
 '	O
or	O
'	O
revision	O
 '	O
(	O
SVN	B-Application
)	O
is	O
a	O
modification	O
that	O
is	O
applied	O
to	O
the	O
repository	B-General_Concept
.	O
</s>
<s>
Commit	B-Protocol
(	O
verb	O
)	O
To	O
commit	B-Protocol
(	O
check	O
in	O
,	O
ci	O
or	O
,	O
more	O
rarely	O
,	O
install	O
,	O
submit	O
or	O
record	O
)	O
is	O
to	O
write	O
or	O
merge	B-General_Concept
the	O
changes	O
made	O
in	O
the	O
working	O
copy	O
back	O
to	O
the	O
repository	B-General_Concept
.	O
</s>
<s>
A	O
commit	B-Protocol
contains	O
metadata	O
,	O
typically	O
the	O
author	O
information	O
and	O
a	O
commit	B-Protocol
message	O
that	O
describes	O
the	O
change	O
.	O
</s>
<s>
Commit	B-Protocol
message	O
A	O
short	O
note	O
,	O
written	O
by	O
the	O
developer	B-Application
,	O
stored	O
with	O
the	O
commit	B-Protocol
,	O
which	O
describes	O
the	O
commit	B-Protocol
.	O
</s>
<s>
Delta	B-Algorithm
compression	I-Algorithm
Most	O
revision	B-Architecture
control	I-Architecture
software	I-Architecture
uses	O
delta	B-Algorithm
compression	I-Algorithm
,	O
which	O
retains	O
only	O
the	O
differences	O
between	O
successive	O
versions	O
of	O
files	O
.	O
</s>
<s>
Export	O
Exporting	O
is	O
the	O
act	O
of	O
obtaining	O
the	O
files	O
from	O
the	O
repository	B-General_Concept
.	O
</s>
<s>
It	O
is	O
similar	O
to	O
checking	O
out	O
except	O
that	O
it	O
creates	O
a	O
clean	O
directory	O
tree	O
without	O
the	O
version-control	B-Architecture
metadata	O
used	O
in	O
a	O
working	O
copy	O
.	O
</s>
<s>
Forward	O
integration	O
The	O
process	O
of	O
merging	O
changes	O
made	O
in	O
the	O
main	O
trunk	B-General_Concept
into	O
a	O
development	O
(	O
feature	O
or	O
team	O
)	O
branch	B-General_Concept
.	O
</s>
<s>
Head	O
Also	O
sometimes	O
called	O
tip	O
,	O
this	O
refers	O
to	O
the	O
most	O
recent	O
commit	B-Protocol
,	O
either	O
to	O
the	O
trunk	B-General_Concept
or	O
to	O
a	O
branch	B-General_Concept
.	O
</s>
<s>
The	O
trunk	B-General_Concept
and	O
each	O
branch	B-General_Concept
have	O
their	O
own	O
head	O
,	O
though	O
HEAD	O
is	O
sometimes	O
loosely	O
used	O
to	O
refer	O
to	O
the	O
trunk	B-General_Concept
.	O
</s>
<s>
Import	O
Importing	O
is	O
the	O
act	O
of	O
copying	O
a	O
local	O
directory	O
tree	O
(	O
that	O
is	O
not	O
currently	O
a	O
working	O
copy	O
)	O
into	O
the	O
repository	B-General_Concept
for	O
the	O
first	O
time	O
.	O
</s>
<s>
Initialize	O
To	O
create	O
a	O
new	O
,	O
empty	O
repository	B-General_Concept
.	O
</s>
<s>
Interleaved	B-Protocol
deltas	I-Protocol
Some	O
revision	B-Architecture
control	I-Architecture
software	I-Architecture
uses	O
Interleaved	B-Protocol
deltas	I-Protocol
,	O
a	O
method	O
that	O
allows	O
storing	O
the	O
history	O
of	O
text	O
based	O
files	O
in	O
a	O
more	O
efficient	O
way	O
than	O
by	O
using	O
Delta	B-Algorithm
compression	I-Algorithm
.	O
</s>
<s>
Label	O
See	O
tag	B-Protocol
.	O
</s>
<s>
Locking	B-Application
When	O
a	O
developer	B-Application
locks	O
a	O
file	O
,	O
no	O
one	O
else	O
can	O
update	O
that	O
file	O
until	O
it	O
is	O
unlocked	O
.	O
</s>
<s>
Locking	B-Application
can	O
be	O
supported	O
by	O
the	O
version	B-Architecture
control	I-Architecture
system	I-Architecture
,	O
or	O
via	O
informal	O
communications	O
between	O
developers	B-Application
(	O
aka	O
social	O
locking	B-Application
)	O
.	O
</s>
<s>
Mainline	B-General_Concept
Similar	O
to	O
trunk	B-General_Concept
,	O
but	O
there	O
can	O
be	O
a	O
mainline	B-General_Concept
for	O
each	O
branch	B-General_Concept
.	O
</s>
<s>
Merge	B-General_Concept
A	O
merge	B-General_Concept
or	O
integration	O
is	O
an	O
operation	O
in	O
which	O
two	O
sets	O
of	O
changes	O
are	O
applied	O
to	O
a	O
file	O
or	O
set	O
of	O
files	O
.	O
</s>
<s>
A	O
user	O
,	O
working	O
on	O
a	O
set	O
of	O
files	O
,	O
updates	O
or	O
syncs	O
their	O
working	O
copy	O
with	O
changes	O
made	O
,	O
and	O
checked	O
into	O
the	O
repository	B-General_Concept
,	O
by	O
other	O
users	O
.	O
</s>
<s>
A	O
user	O
tries	O
to	O
check	O
in	O
files	O
that	O
have	O
been	O
updated	O
by	O
others	O
since	O
the	O
files	O
were	O
checked	O
out	O
,	O
and	O
the	O
revision	B-Architecture
control	I-Architecture
software	I-Architecture
automatically	O
merges	B-General_Concept
the	O
files	O
(	O
typically	O
,	O
after	O
prompting	O
the	O
user	O
if	O
it	O
should	O
proceed	O
with	O
the	O
automatic	O
merge	B-General_Concept
,	O
and	O
in	O
some	O
cases	O
only	O
doing	O
so	O
if	O
the	O
merge	B-General_Concept
can	O
be	O
clearly	O
and	O
reasonably	O
resolved	O
)	O
.	O
</s>
<s>
A	O
branch	B-General_Concept
is	O
created	O
,	O
the	O
code	O
in	O
the	O
files	O
is	O
independently	O
edited	O
,	O
and	O
the	O
updated	O
branch	B-General_Concept
is	O
later	O
incorporated	O
into	O
a	O
single	O
,	O
unified	O
trunk	B-General_Concept
.	O
</s>
<s>
A	O
set	O
of	O
files	O
is	O
branched	O
,	O
a	O
problem	O
that	O
existed	O
before	O
the	O
branching	B-General_Concept
is	O
fixed	O
in	O
one	O
branch	B-General_Concept
,	O
and	O
the	O
fix	O
is	O
then	O
merged	O
into	O
the	O
other	O
branch	B-General_Concept
.	O
</s>
<s>
(	O
This	O
type	O
of	O
selective	O
merge	B-General_Concept
is	O
sometimes	O
known	O
as	O
a	O
cherry	O
pick	O
to	O
distinguish	O
it	O
from	O
the	O
complete	O
merge	B-General_Concept
in	O
the	O
previous	O
case	O
.	O
)	O
</s>
<s>
For	O
example	O
,	O
from	O
a	O
user	O
's	O
workspace	O
into	O
a	O
repository	B-General_Concept
,	O
or	O
from	O
a	O
stream	O
to	O
its	O
parent	O
.	O
</s>
<s>
Pull	O
,	O
push	O
Copy	O
revisions	O
from	O
one	O
repository	B-General_Concept
into	O
another	O
.	O
</s>
<s>
Pull	O
is	O
initiated	O
by	O
the	O
receiving	O
repository	B-General_Concept
,	O
while	O
push	O
is	O
initiated	O
by	O
the	O
source	O
.	O
</s>
<s>
Pull	O
request	O
A	O
developer	B-Application
asking	O
others	O
to	O
merge	B-General_Concept
their	O
"	O
pushed	O
"	O
changes	O
.	O
</s>
<s>
Repository	B-General_Concept
The	O
repository	B-General_Concept
(	O
or	O
"	O
repo	O
"	O
)	O
is	O
where	O
files	O
 '	O
current	O
and	O
historical	O
data	O
are	O
stored	O
,	O
often	O
on	O
a	O
server	B-Application
.	O
</s>
<s>
Reverse	B-Architecture
integration	I-Architecture
The	O
process	O
of	O
merging	O
different	O
team	O
branches	O
into	O
the	O
main	O
trunk	B-General_Concept
of	O
the	O
versioning	B-Architecture
system	I-Architecture
.	O
</s>
<s>
In	O
SVK	O
,	O
a	O
Revision	O
is	O
the	O
state	O
at	O
a	O
point	O
in	O
time	O
of	O
the	O
entire	O
tree	O
in	O
the	O
repository	B-General_Concept
.	O
</s>
<s>
When	O
a	O
shared	O
file	O
is	O
changed	O
in	O
one	O
branch	B-General_Concept
,	O
it	O
is	O
changed	O
in	O
other	O
branches	O
.	O
</s>
<s>
Tag	B-Protocol
A	O
tag	B-Protocol
or	O
label	O
refers	O
to	O
an	O
important	O
snapshot	O
in	O
time	O
,	O
consistent	O
across	O
many	O
files	O
.	O
</s>
<s>
These	O
files	O
at	O
that	O
point	O
may	O
all	O
be	O
tagged	O
with	O
a	O
user-friendly	O
,	O
meaningful	O
name	O
or	O
revision	B-Architecture
number	I-Architecture
.	O
</s>
<s>
Update	O
An	O
update	O
(	O
or	O
sync	O
,	O
but	O
sync	O
can	O
also	O
mean	O
a	O
combined	O
push	O
and	O
pull	O
)	O
merges	B-General_Concept
changes	O
made	O
in	O
the	O
repository	B-General_Concept
(	O
by	O
other	O
people	O
,	O
for	O
example	O
)	O
into	O
the	O
local	O
working	O
copy	O
.	O
</s>
<s>
Working	O
copy	O
The	O
working	O
copy	O
is	O
the	O
local	O
copy	O
of	O
files	O
from	O
a	O
repository	B-General_Concept
,	O
at	O
a	O
specific	O
time	O
or	O
revision	O
.	O
</s>
<s>
All	O
work	O
done	O
to	O
the	O
files	O
in	O
a	O
repository	B-General_Concept
is	O
initially	O
done	O
on	O
a	O
working	O
copy	O
,	O
hence	O
the	O
name	O
.	O
</s>
