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Tablespaces that record extent allocation in the dictionary, are called dictionary managed tablespaces, and tablespaces that record extent allocation in the tablespace header, are called locally managed tablespaces.
By declaring a tablespace as DICTIONARY managed, you are specifying that extent management for segments in this tablespace will be managed using the following dictionary tables: sys.fet$, sys.uet$
A Locally Managed Tablespace is a tablespace that manages its own extents by maintaining a bitmap in each datafile to keep track of the free or used status of blocks in that datafile. Each bit in the bitmap corresponds to a block or a group of blocks