Hi Kurt:
Is this how most databases function?
On further thought on the record locking..
It might be possible for you to take the approach that the real field
is
never edited real time, but only a temp field that is later processed
in the
time sequence (the seconds) 'submitted' in an orderly event loop.
This way,
4 users could be editing the "same field" while seeing that other
users are
doing likewise ("chat room style").
I got into this conversation late; so sorry if my remarks are out of
context. :{`)
From my experience the most common type of locking is record locking.
This can be done on command, usually as a parameter to a database read
command. Once locked, the record cannot be modified by any other user
until it is unlocked--via an unlock command if the record was not
modified or a parameter to the write command when the record is
changed. Some dbs include a parameter to allow/disallow read-only
access to records locked by other users.
Some dbs support "automatic" locking, where the first client to set
current position on a record locks that record until the client's
current position for relative record access (eg: previous,next) in the
db changes.
Some dbs support file locking, where a client can open a db for
exclusive use, or restrict all others to read-only access. This is
more prevalent in "flat file" databases.
Since fields are generally sub components of records, field locking is
not practical: one can't effectively lock a field without locking the
entire record. Some dbs deal with this by setting authority levels in
user profiles and specifying the minimum authority for a user to (a)
view and/or (b) modify individual fields in each record's data
dictionary.
The actual locking mechanisms vary. In some dbs, especially older
non-server multi-user environments, records are locked by actually
flagging the record and writing it back to the db. The means:
* a locked record must be rewritten even if it is not changed in order
to unlock it, and
* records locked at system crash must be unlocked during system recovery
With client/server systems, the server can maintain a locked record
table in RAM for each database.
Rob Cozens
CCW, Serendipity Software Company
"And I, which was two fooles, do so grow three;
Who are a little wise, the best fooles bee."
from "The Triple Foole" by John Donne (1572-1631)
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