<s>
In	O
temporal	O
databases	O
,	O
transaction	B-General_Concept
time	I-General_Concept
(	O
TT	O
)	O
is	O
the	O
time	O
during	O
which	O
a	O
fact	O
stored	O
in	O
the	O
database	O
is	O
considered	O
to	O
be	O
true	O
.	O
</s>
<s>
As	O
of	O
December	O
2011	O
,	O
ISO/IEC	O
9075	O
,	O
Database	O
Language	O
SQL:2011	B-Language
Part	O
2	O
:	O
SQL/Foundation	O
included	O
clauses	O
in	O
table	O
definitions	O
to	O
define	O
"	O
system-versioned	O
tables	O
"	O
(	O
that	O
is	O
,	O
transaction-time	B-General_Concept
tables	O
)	O
.	O
</s>
<s>
When	O
the	O
ending	O
transaction	B-General_Concept
time	I-General_Concept
is	O
unknown	O
,	O
it	O
may	O
be	O
considered	O
as	O
"	O
Until	O
Changed	O
"	O
.	O
</s>
