Network database link is created and managed by a network domain service. A
network database link can be used when any user of any database in the network specifies a global object name in a SQL statement or object definition.
ORACLE databases data is stored in data blocks. One data block corresponds to a specific number of bytes of physical database space on disk.
A data block size is specified for each ORACLE database when the database is
created. A database users and allocated free database space in ORACLE datablocks. Block size is specified in INIT.ORA file and cannt be changed latter.
ORACLE database is comprised of three types of files. One or more Data files, two are more Redo Log files, and one or more Control files.
Tablespaces and the Databases Schema Objects.