Database Reference
In-Depth Information
38. Let
),whereR
s
is a source schema consisting of a binary predicate
U
,
R
t
is a target schema consisting of a binary predicate
V
and
M
=(R
s
,
R
t
,
Σ
Σ
=
{∀
x
∃
y
∀
z
(
U
(
x
,
z
)
→
is closed under target homomorphisms, admits universal so-
lutions and reflects source homomorphisms.
39. (Source:
ten Cate and Kolaitis
(
2009
))
Complete the proof of
Theorem 21.5
.
40. (Source:
ten Cate and Kolaitis
(
2009
))
Let
M
be the mapping defined in
Example 21.8
. Prove that
M
is closed under target
homomorphisms, admits universal solutions, reflects source homomorphisms and is
closed under target intersection.
41. (Source:
ten Cate and Kolaitis
(
2009
))
Prove
Lemma 21.9
.
V
(
y
,
z
))
}
. Prove that
M
