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MODES OF ACCESS

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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
1Find (read), replace, add, delete entries (QUERY requests IMAGE dynamically lock and unlock the data base when accessing it)
2Find and replace entries
3* or 4Find, replace, add, and delete entries
5Find entries (QUERY locks and unlocks)
6, 7*, or 8Find 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
    5The 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.
    6Mode 2 users can replace entries, and one mode 4 user can replace, add, or delete; or mode 8 users can read entries.
    7You have exclusive access to the data base.
    8No 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
1QUERY 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.)
3You have exclusive access to the data base.
4You 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

[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.



STRUCTURE OF THE DATA BASE

PASSWORDS