|
|
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
one mode 3 user
one mode 7 user
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.
Figure 1-3 IMAGE/QUERY Environments
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.
|