iX V6.5 (30391-90011)

98 Chapter4

Using the Database

Opening the Database

option, which can permit you to update the values of detail data set search and sort

items, is not available in this mode. Therefore, the access mode 2 user is able to read all

data entries and update some data entries, but is not permitted to add or delete data

entries in any data set.

The programmer must be aware of the possibility that other access mode 2 users are

simultaneously updating data entries. In many applications, it may be possible to

arrange for each user's process to update unique data entries or data items so that the

database will correctly reﬂect all changes, even data items in the same entry updated

by different processes. On the other hand, if two or more processes update the same

data items of the same entry, the database will reﬂect only the latest values. Locking

can be used, if desired, to coordinate update sequences to an entry or to coordinate with

access mode 6 readers.

• Access Mode 3. The database is opened for exclusive modify access. If any other users

are accessing the database, it cannot be opened in this mode. All TurboIMAGE/XL

procedures are available to the access mode 3 user. The critical item update (CIUPDATE)

option, which can permit you to update the values of detail data set search and sort

items, is available in this mode. No other concurrent process is permitted to gain any

type of access to the database.

• Access Mode 4. The database is opened for semi-exclusive modify access. Only one

access mode 4 user can access the database, and all other current users must be in

access mode 6 (read only). The access mode 4 user is permitted to call any

TurboIMAGE/XL procedure and has complete control over database content. The

critical item update (CIUPDATE) option, which can permit you to update the values of

detail data set search and sort items, is available in this mode. Other read-only users

are permitted concurrent access to the database in mode 4, but not in mode 3. Locking

can be used to coordinate with access mode 6 readers.

• Access Mode 5. The database is opened for shared read access. All other concurrent

users must be in access mode 1 or 5. Access mode 5 operates the same as access mode 1,

except that the DBUPDATE, DBPUT, and DBDELETE procedures, which alter the

database, are disabled for the access mode 5 user. Locking can be used, if desired, to

ensure that data is not being modiﬁed while you are reading it.

Access mode 5 is appropriate for inquiry-type applications if they can tolerate the

possibility of database modiﬁcations taking place simultaneously with access mode 1

users.

• Access Mode 6. The database is opened for shared read access. Concurrent users must

be in access mode 2, 4, 6, or 8. Access mode 6 can also be used while the database is

being stored with the TurboIMAGE/XL utility program DBSTORE. Some of these modes

are incompatible with each other as shown in the preceding discussion of concurrent

access modes. All TurboIMAGE/XL procedures that alter the database are disabled.

Locking can be used to synchronize with users who are concurrently updating.

Access mode 6 is appropriate for inquiry-type applications if they can tolerate the

possibility of database modiﬁcations taking place simultaneously with access mode 2

and 4 users.