Schema evolution involves defining flavored object groups. Specifically,
related collections of replicated tables and other database objects,
which are defined as belonging to an object group, are given different
"flavors." A flavor describes different subsets of the objects and even
different subsets of the columns in the master tables. In one embodiment,
when one site in a distributed database system propagates changes to a
replicated database object, the current flavor for the site is also
transmitted, so that the destination site can make the necessary
adjustments in the uploaded changes by dropping the values for obsolete
columns and using default values for new columns.