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Фрагмент инструкции
The
programmer
m
ust
b e
a
w
are
of
the
p ossibility
that
other
access
mo
de
2
users
are
simultaneously
up dating
data
en
tries.
In
man
y
applications,
it
may
b e
p ossible
to
arrange
for
eac
h
user's
pro cess
to
up date
unique
data
en
tries
or
data
items
so
that
the
database
will
correctly
re ect
all
c
hanges,
ev
en
data
items
in
the
same
en
try
up dated
b
y
dieren
t
pro cesses.
On
the
other
hand,
if
t
w
o
or
more
pro cesses
up date
the
same
data
items
of
the
same
en
try
,
the
database
will
re ect
only
the
latest
v
alues.
Lo c
king
can
b e
used,
if
desired,
to
co ordinate
up date
sequences
to
an
en
try
or
to
co ordinate
with
access
mo
de
6
readers.
Access
Mo de
3.
The
database
is
op ened
for
exclusiv
e
mo
dify
access.
If
an
y
other
users
are
accessing
the
database,
it
cannot
b e
op ened
in
this
mo
de.
All
T
urb oIMA
GE/XL
pro cedures
are
a
v
ailable
to
the
access
mo
de
3
user.
The
critical
item
up date
(CIUPD
A
TE)
option,
whic
h
can
p ermit
y
ou
to
up date
the
v
alues
of
detail
data
set
searc
h
and
sort
items,
is
a
v
ailable
in
this
mo
de.
No
other
concurren
t
pro cess
is
p ermitted
to
gain
an
y
t
yp e
of
access
to
the
database.
Access
Mo de
4.
The
database
is
op ened
for
semi-exclusive
mo
dify
access.
Only
one
access
mo
de
4
user
can
access
the
database,
and
all
other
curren
t
users
m
ust
b e
in
access
mo
de
6
(read
only).
The
access
mo
de
4
user
is
p ermitted
to
call
an
y
T
urb oIMA
GE/XL
pro cedure
and
has
complete
con
trol
o
v
er
database
con
ten
t.
The
critical
item
up date
(CIUPD
A
TE)
option,
whic
h
can
p ermit
y
ou
to
up date
the
v
alues
of
detail
data
set
searc
h
and
sort
items,
is
a
v
ailable
in
this
mo
de.
Other
read-only
users
are
p ermitted
concurren
t
access
to
the
database
in
mo
de
4,
but
not
in
mo
de
3.
Lo c
king
can
b e
used
to
co ordinate
with
access
mo
de
6
readers.
Access
Mo de
5.
The
database
is
op ened
for
shared
read
access.
All
other
concurren
t
users
m
ust
b e
in
access
mo
de
1
or
5.
Access
mo
de
5
op erates
the
same
as
access
mo
de
1,
except
that
the
DBUPD
A
TE,
DBPUT,
and
DBDELETE
pro cedures,
whic
h
alter
the
database,
are
disabled
for
the
access
mo
de
5
user.
Lo c
king
can
b e
used,
if
desired,
to
ensure
that
data
is
not
b eing
mo
died
while
y
ou
are
reading
it.
Access
mo
de
5
is
appropriate
for
inquiry-typ e
applications
if
they
can
tolerate
the
p ossibility
of
database
mo
dications
taking
place
simultaneously
with
access
mo
de
1
users.
Access
Mo de
6.
The
database
is
op ened
for
shared
read
access.
Concurren
t
users
m
ust
b e
in
access
mo
de
2,
4,
6,
or
8.
Access
mo
de
6
can
also
b e
used
while
the
database
is
b eing
stored
with
the
T
urb oIMA
GE/XL
utilit y
program
DBSTORE.
Some
of
these
mo
des
are
incompatible
with
eac
h
other
as
sho
wn
in
the
preceding
discussion
of
concurren
t
access
mo
des.
All
T
urb oIMA
GE/XL
pro cedures
that
alter
the
database
are
disabled.
Lo c
king
can
b e
used
to
sync
hronize
with
users
who
are
concurren
tly
up dating.
Access
mo
de
6
is
appropriate
for
inquiry-typ e
applications
if
they
can
tolerate
the
p ossibility
of
database
mo
dications
taking
place
simultaneously
with
access
mo
de
2
and
4
users.
Access
Mo de
7.
The
database
is
op ened
for
exclusiv
e
read
access.
No
other
users
can
access
the
database
concurren
tly
.
Access
mo
de
7
op erates
the
same
as
access
mo
de
3,
except
that
the
DBUPD
A
TE,
DBPUT,
and
DBDELETE
pro cedures,
whic
h
alter
the
database,
are
disabled
for
the
access
mo
de
7
user.
Access
Mo de
8.
The
database
is
op ened
for
shared
read
access.
Concurren
t
users
m
ust
either
b e
in
access
mo
de
6
or
8,
or
using
the
T
urb oIMA
GE/XL
utilit y
,
DBSTORE.
T
urb oIMA
GE/XL
pro cedures
that
alter
the
database
are
not
p ermitted.
Because
access
mo
de
8
allo
ws
only
concurren
t
readers,
a
user
program
with
this
access
mo
de
can
b e
assured
that
the
database
v
alues
it
reads
are
unc
hanging.
4-6
Using
the
Database
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Программное обеспечение - MPE/iX 6.5 Operating System (1.85 mb)