Database Reference
In-Depth Information
A schedule:
O
H,1
, …..,
O
H,K
; O
L,1
, ….., O
L,m
; O
H,K+1
, ….., O
H,
n
;
C
H
Invisible area of T
H
T
H
Suspends T
L
Resumes T
H
Figure 7.1
The notion of the invisible area.
transaction,
T
L
; the time when
T
H
executes again is called the
invisible area to
T
H
. Defining the invisible area prevents the high
classification level transaction,
T
H
, from reading new versions
created by the low transaction,
T
L
, running within this area;
otherwise,
T
H
may have the problem of the retrieval anomaly.
• Figure 7.1 presents the definition of the invisible area with
the execution of the high classification level transactions,
T
H
;
the low classification level transactions,
T
L
; the high clas-
sification level operations,
O
H
; the low classification level
transactions,
O
L
; and the high classification level transactions
commit,
C
H
.
• Definition 3: A conflict transaction set of the high transaction
T
H
is defined as
C
-set
T
H
and contains the transactions that
enter an invisible area of
T
H
. Suppose that
T
L
is entered to
the scheduler. If
R
-set
T
H
∩
W
-set
T
L
≠ φ, then
T
L
∈
C
-set
T
H
.
• Definition 4: The transaction identifier (TID) is attached to
low transaction
T
L
. The term “t-lock” will be used for the
attachment and detachment of a TID. When
T
L
exists in
the invisible area of
T
H
, its TID will be in the
C
-set
T
H
of
the blocked high transaction
T
H
.
Rajwinder Singh [95] adds a transaction into
T
L
∈
C
-set
T
H
.
Singh 's
model reads the recent version by the high classification level trans-
action
T
H
and shows that the size of
C
-set
T
H
can be decreased by
increasing the condition without effect on the security of the mul-
tilevel relational database. Singh divided
R
-set
T
H
into two parts:
R
-set
done
T
H
and
R
-set
remaining
T
H
:
R
-set
done
T
H
∪
R
-set
remaining
T
H
=
R
-set
T
H
.
R
-set
done
T
H
consists of the data read by
T
H
.
R
-set
remaining
T
H
consists of the data to be read by
T
H
.
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