If the bridge is closed, the island
exists but no traffic flow is possible. In Oracle terms, if the instance is up, data can
flow in and out of the database. The physical state of the database is changing. If the
instance is down, users cannot access the database even though it still exists physically.
The database is static: no changes can occur to it. When the instance comes
back into service, the data will be there waiting for it.
Oracle Database Structure
Oracle??™s database structures include tablespaces, control files, redo log files, archived
logs, block change tracking files, Flashback logs, and recovery backup (RMAN) files.
This section introduces many of the structures and other components that make up a
complete database.
Tablespaces
All of the data stored within an Oracle database must reside in a tablespace. A
tablespace is a logical structure; you can??™t look at the operating system and see a
tablespace. Each tablespace is composed of physical structures called datafiles; each
tablespace must consist of one or more datafiles, and each datafile can belong to only
one tablespace.
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