Because many users access and change data in a relational database, the database manager must allow users to make these changes while ensuring that data integrity is preserved.
Concurrency is not an issue for global temporary tables, because they are available only to the application that declares or creates them.
A federated database system supports applications and users submitting SQL statements that reference two or more database management systems (DBMSs) in a single statement. To reference such data sources (each consisting of a DBMS and data), the DB2® server uses nicknames. Nicknames are aliases for objects in other DBMSs. In a federated system, the DB2 server relies on the concurrency control protocols of the database manager that hosts the requested data.
A DB2 federated system provides location transparency for database objects. For example, if information about tables and views is moved, references to that information (through nicknames) can be updated without changing the applications that request this information. When an application accesses data through nicknames, the DB2 server relies on concurrency control protocols at the data source to ensure that isolation levels are enforced. Although the DB2 server tries to match the isolation level that is requested at the data source with a logical equivalent, results can vary, depending on data source capabilities.