<s>
A	O
Uniform	B-Operating_System
Type	I-Operating_System
Identifier	I-Operating_System
(	O
UTI	O
)	O
is	O
a	O
text	O
string	O
used	O
on	O
software	O
provided	O
by	O
Apple	O
Inc	O
.	O
to	O
uniquely	O
identify	O
a	O
given	O
class	O
or	O
type	O
of	O
item	O
.	O
</s>
<s>
Support	O
for	O
UTIs	O
was	O
added	O
in	O
the	O
Mac	B-Application
OS	I-Application
X	I-Application
10.4	I-Application
operating	B-General_Concept
system	I-General_Concept
,	O
integrated	O
into	O
the	O
Spotlight	B-Application
desktop	O
search	O
technology	O
,	O
which	O
uses	O
UTIs	O
to	O
categorize	O
documents	O
.	O
</s>
<s>
One	O
of	O
the	O
primary	O
design	O
goals	O
of	O
UTIs	O
was	O
to	O
eliminate	O
the	O
ambiguities	O
and	O
problems	O
associated	O
with	O
inferring	O
a	O
file	O
's	O
content	O
from	O
its	O
MIME	B-Protocol
type	I-Protocol
,	O
filename	O
extension	O
,	O
or	O
type	O
or	O
creator	B-Operating_System
code	I-Operating_System
.	O
</s>
<s>
UTIs	O
use	O
a	O
reverse-DNS	B-Protocol
naming	O
structure	O
.	O
</s>
<s>
Names	O
may	O
include	O
the	O
ASCII	B-Protocol
characters	I-Protocol
A	O
–	O
Z	O
,	O
a	O
–	O
z	O
,	O
0	O
–	O
9	O
,	O
hyphen	O
("-"	O
)	O
,	O
and	O
period	O
(	O
"	O
.	O
</s>
<s>
Colons	O
and	O
slashes	O
are	O
prohibited	O
for	O
compatibility	O
with	O
Macintosh	B-Device
and	O
POSIX	O
file	O
path	O
conventions	O
.	O
</s>
<s>
UTIs	O
support	O
multiple	B-Application
inheritance	I-Application
,	O
allowing	O
files	O
to	O
be	O
identified	O
with	O
any	O
number	O
of	O
relevant	O
types	O
,	O
as	O
appropriate	O
to	O
the	O
contained	O
data	O
.	O
</s>
<s>
One	O
of	O
the	O
difficulties	O
in	O
maintaining	O
a	O
user-accessible	O
operating	B-General_Concept
system	I-General_Concept
is	O
establishing	O
connections	O
between	O
data	O
types	O
and	O
the	O
applications	O
or	O
processes	O
that	O
can	O
effectively	O
use	O
such	O
data	O
.	O
</s>
<s>
In	O
early	O
computer	O
systems	O
–	O
particularly	O
DOS	B-Device
,	O
its	O
variants	O
,	O
and	O
some	O
versions	O
of	O
Windows	O
–	O
file	O
associations	O
are	O
maintained	O
by	O
file	O
extensions	O
.	O
</s>
<s>
Beginning	O
with	O
System	B-Operating_System
1	I-Operating_System
,	O
Macintosh	B-Device
operating	B-General_Concept
systems	I-General_Concept
have	O
attached	O
type	O
codes	O
and	O
creator	B-Operating_System
codes	I-Operating_System
as	O
part	O
of	O
the	O
file	O
metadata	O
.	O
</s>
<s>
These	O
four-character	O
codes	O
were	O
designed	O
to	O
specify	O
both	O
the	O
application	O
that	O
created	O
the	O
file	O
(	O
the	O
creator	B-Operating_System
code	I-Operating_System
)	O
and	O
the	O
specific	O
type	O
of	O
the	O
file	O
(	O
the	O
type	O
code	O
)	O
so	O
that	O
other	O
applications	O
could	O
easily	O
open	O
and	O
process	O
the	O
file	O
data	O
.	O
</s>
<s>
However	O
,	O
while	O
type	O
and	O
creator	B-Operating_System
codes	I-Operating_System
extended	O
the	O
flexibility	O
of	O
the	O
system	O
—	O
a	O
particular	O
type	O
of	O
file	O
was	O
not	O
restricted	O
to	O
opening	O
in	O
a	O
particular	O
application	O
—	O
they	O
suffered	O
many	O
of	O
the	O
same	O
problems	O
as	O
file	O
extensions	O
.	O
</s>
<s>
Type	O
and	O
creator	B-Operating_System
codes	I-Operating_System
could	O
be	O
lost	O
when	O
files	O
were	O
transferred	O
across	O
non-Macintosh	O
systems	O
(	O
such	O
as	O
Unix-based	O
servers	O
)	O
,	O
and	O
the	O
plethora	O
of	O
type	O
codes	O
made	O
identification	O
problematic	O
.	O
</s>
<s>
In	O
addition	O
,	O
the	O
classic	B-Application
Mac	I-Application
OS	I-Application
did	O
not	O
recognize	O
file	O
extensions	O
at	O
all	O
,	O
leading	O
to	O
unrecognized	O
file	O
errors	O
when	O
files	O
were	O
transferred	O
from	O
DOS/Windows	O
systems	O
.	O
</s>
<s>
OPENSTEP	B-Operating_System
,	O
which	O
formed	O
the	O
basis	O
of	O
Mac	B-Operating_System
OS	I-Operating_System
X	I-Operating_System
,	O
used	O
extensions	O
,	O
and	O
early	O
versions	O
of	O
Mac	B-Operating_System
OS	I-Operating_System
X	I-Operating_System
followed	O
suit	O
.	O
</s>
<s>
This	O
led	O
to	O
some	O
controversy	O
with	O
users	O
and	O
developers	O
coming	O
to	O
OS	B-Operating_System
X	I-Operating_System
from	O
NeXT	O
or	O
Windows	O
origins	O
advocating	O
for	O
continued	O
use	O
of	O
file	O
extensions	O
,	O
and	O
those	O
coming	O
from	O
Classic	B-Application
Mac	I-Application
OS	I-Application
urging	O
Apple	O
to	O
replace	O
or	O
supplement	O
file	O
extensions	O
with	O
type	O
and	O
creators	O
.	O
</s>
<s>
Other	O
file	O
identification	O
types	O
exist	O
:	O
for	O
example	O
,	O
MIME	B-Application
types	I-Application
are	O
used	O
for	O
identifying	O
data	O
that	O
is	O
transferred	O
over	O
the	O
web	O
.	O
</s>
<s>
Apple	O
's	O
macOS	B-Application
continues	O
to	O
support	O
other	O
forms	O
of	O
file	O
association	O
,	O
and	O
contains	O
utilities	O
for	O
translating	O
between	O
them	O
,	O
but	O
will	O
use	O
UTIs	O
by	O
preference	O
where	O
available	O
.	O
</s>
<s>
Dynamic	O
UTIs	O
can	O
be	O
created	O
as	O
needed	O
by	O
applications	O
;	O
these	O
have	O
the	O
prefix	O
and	O
take	O
the	O
form	O
of	O
"	O
a	O
UTI-compatible	O
wrapper	O
around	O
an	O
otherwise	O
unknown	O
filename	O
extension	O
,	O
MIME	B-Protocol
type	I-Protocol
,	O
OSType	B-Application
,	O
and	O
so	O
on.	O
"	O
</s>
<s>
Third-party	O
applications	O
can	O
add	O
UTIs	O
to	O
the	O
database	O
maintained	O
by	O
macOS	B-Application
by	O
"	O
exporting	O
"	O
UTIs	O
declared	O
within	O
the	O
application	O
package	O
.	O
</s>
<s>
Because	O
new	O
UTIs	O
can	O
be	O
declared	O
to	O
"	O
conform	O
to	O
"	O
existing	O
system	O
UTIs	O
,	O
and	O
declarations	O
can	O
associate	O
the	O
new	O
UTIs	O
with	O
file	O
extensions	O
,	O
an	O
exported	O
declaration	O
alone	O
can	O
provide	O
the	O
operating	B-General_Concept
system	I-General_Concept
with	O
enough	O
information	O
to	O
enable	O
new	O
functions	O
,	O
such	O
as	O
enabling	O
Quick	B-Operating_System
Look	I-Operating_System
for	O
new	O
file	O
types	O
.	O
</s>
<s>
To	O
get	O
the	O
UTI	O
of	O
a	O
given	O
file	O
,	O
use	O
the	O
mdls	B-Application
(	O
meta	O
data	O
list	O
,	O
part	O
of	O
Spotlight	B-Application
)	O
command	O
in	O
the	O
Terminal	B-Application
.	O
</s>
