Database Reference
In-Depth Information
Σ
RE
algebra term
R-algebra operation
f
(k)
r
C
=
t
1
⊗···⊗
t
k
(Cartesian
R
C
(Cartesian
k
-ary function)
⊗
:
R
1
×···×
R
k
→
product)
r
S
0
=
r
C
WHERE
C
S
J
(Select by
C(
x
)
+
in
−
1
:
R
C
R
S
0
(Inverse-inclusion function)
Join by
S
J
)
r
S
1
=
EXTEND
r
S
0
ADD
a
N
+
1
, name
N
+
1
,t
i
1
...
r
S
j
=
EXTEND
r
S
j
−
1
ADD
a
N
+
j
, name
N
+
j
,t
i
j
...
r
S
m
=
EXTEND
r
S
m
−
1
ADD
a
N
+
m
, name
N
+
m
,t
i
m
f
R
S
0
,t
i
1
:
R
S
1
,
with
π
[
1
,...,N
]
(R
S
1
)
R
S
0
→
=
R
S
0
...
f
R
S
j
−
1
,t
i
j
:
R
S
j
−
1
→
R
S
j
...
f
R
S
m
−
1
,t
i
m
:
R
S
m
−
1
→
R
S
m
r
q
r
S
m
(Project on
S
)
=[
S
]
π
S
R
q
(Projection function)
:
R
S
m
→
(R
B
UNION
R
q
)
→
R
B
(Union)
in
:
R
q
→
R
B
(Injective function)
Reference
1. E.F. Codd, Relational completeness of data base sublanguages, in
Data Base Systems
. Courant
Computer Science Symposia Series, vol. 6 (Prentice Hall, Englewood Cliffs, 1972)
