In a database, a database manager can generate a view, which, in concept, is a
subset of the database, which is placed outside the database for use without disturbing
the database, and without disturbance by others using the database. The subset,
or view, can be understood as a collection of rows, or tuples, of data copied from
the database. With views existing, multiple copies of data within the database
now exist: the original in the database, and copies in the views. If one of these
is changed, without corresponding changes made in the others, then inconsistencies
occur, which cannot be tolerated. Under the invention, when a user seeks a lock
on a view, indicating that a change may be imminent, the invention locks a superset
of the tuples in the database from which the view is derived. A superset is a set
which contains the set of tuples of the view, plus possibly others. Thus, more
tuples are locked than strictly necessary. The excess locking is tolerated because
other benefits are obtained.
