<s>
SQLf	B-Language
is	O
a	O
SQL	B-Language
extended	O
with	O
fuzzy	O
set	O
theory	O
application	O
for	O
expressing	O
flexible	O
(	O
fuzzy	O
)	O
queries	O
to	O
traditional	O
(	O
or	O
″Regular″	O
)	O
Relational	O
Databases	O
.	O
</s>
<s>
Among	O
the	O
known	O
extensions	O
proposed	O
to	O
SQL	B-Language
,	O
at	O
the	O
present	O
time	O
,	O
this	O
is	O
the	O
most	O
complete	O
,	O
because	O
it	O
allows	O
the	O
use	O
of	O
diverse	O
fuzzy	O
elements	O
in	O
all	O
the	O
constructions	O
of	O
the	O
language	O
SQL	B-Language
.	O
</s>
<s>
SQLf	B-Language
is	O
the	O
only	O
known	O
proposal	O
of	O
flexible	O
query	O
system	O
allowing	O
linguistic	O
quantification	O
over	O
set	O
of	O
rows	O
in	O
queries	O
,	O
achieved	O
through	O
the	O
extension	O
of	O
SQL	B-Language
nesting	O
and	O
partitioning	O
structures	O
with	O
fuzzy	O
quantifiers	O
.	O
</s>
<s>
The	O
fundamental	O
querying	O
structure	O
of	O
SQLf	B-Language
is	O
the	O
multi-relational	O
block	O
.	O
</s>
<s>
The	O
conception	O
of	O
this	O
structure	O
is	O
based	O
on	O
the	O
three	O
basic	O
operations	O
of	O
the	O
relational	B-Algorithm
algebra	I-Algorithm
:	O
projection	B-Algorithm
,	O
cartesian	O
product	O
and	O
selection	B-Algorithm
,	O
and	O
the	O
application	O
of	O
fuzzy	O
sets’	O
concepts	O
.	O
</s>
<s>
The	O
result	O
of	O
a	O
SQLf	B-Language
query	O
is	O
a	O
fuzzy	O
set	O
of	O
rows	O
that	O
is	O
a	O
fuzzy	O
relation	O
instead	O
of	O
a	O
regular	O
relation	O
.	O
</s>
<s>
A	O
basic	O
block	O
in	O
SQLf	B-Language
consists	O
of	O
a	O
SELECT	B-Language
clause	O
,	O
a	O
FROM	B-Language
clause	O
and	O
an	O
optional	O
WHERE	B-Language
clause	O
.	O
</s>
<s>
The	O
SELECT	B-Language
clause	O
corresponds	O
to	O
the	O
projection	B-Algorithm
.	O
</s>
<s>
The	O
SELECT	B-Language
clause	O
specifies	O
also	O
a	O
calibration	O
that	O
is	O
intended	O
to	O
restrict	O
the	O
set	O
of	O
rows	O
retrieved	O
.	O
</s>
<s>
The	O
FROM	B-Language
clause	O
corresponds	O
to	O
the	O
Cartesian	O
Product	O
.	O
</s>
<s>
The	O
WHERE	B-Language
clause	O
corresponds	O
to	O
the	O
selection	B-Algorithm
.	O
</s>
<s>
The	O
following	O
is	O
an	O
example	O
of	O
a	O
SELECT	B-Language
query	O
that	O
returns	O
a	O
list	O
of	O
hotels	O
that	O
are	O
cheap	O
.	O
</s>
<s>
The	O
query	O
retrieves	O
all	O
rows	O
from	B-Language
the	O
Hotels	O
table	O
that	O
satisfice	O
the	O
fuzzy	O
predicate	O
cheap	O
defined	O
by	O
the	O
fuzzy	O
set	O
μ	O
=(	O
,	O
,	O
25	O
,	O
30	O
)	O
.	O
</s>
