Database Reference
In-Depth Information
The I/O memory (a subset of registers) will be used alternatively in order to
receive the data from the host universal machine, and to send the obtained results
(for example, obtained relation from a 'SELECT...' SQL statements in the source
program
P
), while the data-memory is the subset of registers used to load the whole
database from the permanent (disk) memory, and for their dynamic updates (by
Buffer Manager) during the execution of a program
P
.
The System memory is the subset of registers used for the synchronization, Ap-
plication Plane (set of embedded programs, i.e., the arrows in
RA
category), and all
internal computations. Such a categorial machine has to be synchronized with the
host universal machine
M
R
by additional set of operators in
{
NOP
,
RETURN
,
ERR
,
VCON
,
COM
,
ACOM
,
DEC
,
RBACK
}
,
and we will use the first four registers
x
i
and test functions
t
i
for such features, as
follows:
Definition 40
A Categorial RDB machine
M
R
is defined by
RMI
=
(S
R
, Oper
R
, Te s t
R
, In
R
, In
ER
, Out
R
)
with the following features (we assume that during the execution of a program all
states in
S
R
are progressively enumerated in the way that
st
(k)
st
(k
=
+
1
)
):
1.
•
x
1
is the memory register used to save the number
n
of the program
P
n
in
Application Plane, requested to be executed from
M
U
by CALL
n
;
•
x
2
is the memory register for the error-condition. Its default value (imposed
in
st
(
0
)
) is equal to 0. After the commitment or execution of 'SELECT...'
for an inconsistent database it is imposed to 1;
•
x
3
is the memory register used to sign the synchpoints (of transactions) for a
database with
x
3
=
1;
•
x
4
is the memory register used to determine the address of a program to exe-
cute.
Te s t
R
, where for a state
st
(k)
∈
S
R
and
i
=
1
,
2
,
3
,
4,
t
i
(st
(k))
=
2.
{
t
1
,t
2
,t
3
,t
4
}⊆
1if
x
i
is equal to 0; 1, otherwise.
3.
Σ
RA
∪{
NOP
,
RETURN
,
ERR
,
VCON
,
COM
,
ACOM
,
DEC
,
RBACK
}⊆
Oper
R
, where
Σ
RA
are the algebra operators used in the category
RA
, and
•
NOP does not change the state of the machine;
•
RETURN is a function which assigns 0 to
x
1
;
•
ERR is function which assigns 1 to
x
2
;
•
VCON is function which assigns 0 to
x
2
if the database in the dynamic mem-
ory of Buffer Manager is consistent in the current machine's state; 1 other-
wise;
•
COM is function which assigns 1 to
x
3
, then changes the state by rewriting a
database from the working memory (Buffer Manager) into the physical stor-
age memory (which is also a part of the state of
M
R
);
