Each person using QUERY to access a data base must specify
one of the 8 modes of access. The following table lists the capabilities
you will have in each mode.
| MODE | CAPABILITIES |
|---|
| 1 | Find (read), replace,
add, delete entries (QUERY requests IMAGE dynamically lock and unlock
the data base when accessing it) |
| 2 | Find and replace
entries |
| 3* or 4 | Find, replace,
add, and delete entries |
| 5 | Find entries (QUERY
locks and unlocks) |
| 6, 7*, or 8 | Find entries |
* Modes 3 and 7 give you exclusive access to the data base.
All other modes allow others to share the data base.
A data base can only be shared in certain situations or environments.
The mode you specify must be acceptable for the environment already
established by other IMAGE and QUERY users (if any) when you open
the data base. Here is a summary of the acceptable environments:
multiple mode 1 and
mode 5 users
multiple mode 6 and mode 2 users
multiple mode 6 users and one mode 4 user
multiple mode 6 and mode 8 users
Subsets of these environments are also allowed. For example,
there may be all mode 6 users or all mode 8 users. There may also
be one mode 1 user or all mode 5 users and so forth.
If a mode 3 or mode 7 user is currently accessing the data
base that you want to access, you must wait until that user either
terminates their IMAGE or QUERY session or accesses a different
data base. This is true any time you try to access a data base with
a mode which is incompatible with other users accessing the same
data base. Changing your mode of access may enable you to access
the data base.
When deciding which mode to use, you should consider the following:
If you merely want
to find information and examine or report on it, you should open
the data base with a find (read-only) mode, thus allowing other
users as much capability as possible. The following table gives
the result of using each read-only mode.
| MODE | RESULT |
|---|
| 5 | The data base is
locked for some operations and may slow the rate of activity somewhat.
If mode 1 or mode 5 users are already accessing the data base, you
must use mode 5. |
| 6 | Mode 2 users can
replace entries, and one mode 4 user can replace, add, or delete; or
mode 8 users can read entries. |
| 7 | You have exclusive access to the
data base. |
| 8 | No other users can replace, add, or delete
entries. |
An important advantage of using modes 5 through 8 is
that the data base is opened for reading only. As a result, you
are more likely to gain access to the data base by avoiding restrictions
due to the MPE account structure. Also, the files are not marked
for inclusion in the MPE system backup since they are not altered
in any way. This saves time when the daily system backup procedure
is executed.
If you want to find information and replace data
in existing entries but do not need to add or delete any entries
(and do not want anyone else to add or delete entries), you should
open the data base with mode 2.
If you want to perform all the operations, including
adding and deleting entries, you should open with mode 1, 3, or
4. The following table gives the result of using each of these modes.
| MODE | RESULT |
|---|
| 1 | QUERY locks and
unlocks the data base while performing operations. Other users are
able to add and delete entries. (The previous comments for mode
5 apply here also.) |
| 3 | You have exclusive
access to the data base. |
| 4 | You have exclusive ability to
change the data base but mode 6 users are able to read while you
make changes. |
Figure 1-3 “IMAGE/QUERY Environments” illustrates acceptable IMAGE/QUERY
environments. Users at terminals can operate IMAGE or QUERY simultaneously.
A single user indicates that only one user may specify that mode.
Two users indicates that multiple users may specify that mode. Terminals
indicate the modes which are incompatible with the current environment.
The capability of each user is abbreviated as follows: F = find,
R = replace, A = add, D = delete.
Logging and Mode Selection |
 |
Opening the data base in modes 1 through 4 allows data base
modifications to be logged to a log file and subsequently recovered
if there is a system failure. If the data base administrator has
enabled the data base for logging, certain requirements of the logging system
must be met before the data base can be accessed in modes 1 through
4.
These requirements are the responsibility of the data base
administrator and console operator, and are discussed in the TurboIMAGE/XL
Database Management System Reference Manual. If any
of these requirements are not satisfied, an IMAGE error message is
returned.
Printable version
