
The DDBMS maintains a directory of information about tables, views, fragments,
replicas, user access rights, etc. which it uses in interpreting queries and in compiling
and executing application programs. Just as a distribution schema for the user data
must be designed, so must a distribution schema for the DDBMS directory. If any user
is to be able to query any data in the database, then the DDBMS query processor must
have access to the full directory. Two possibilities are:
Store the directory at a single site.
Replicate the directory at every site.
Storing the directory at a single site destroys the ability of other sites to function
independently ...