1.User's O.S account has O.S  previleges.

2.The user is granted the SYSDBA or SYSOPER previleges and database user the password files to authenticate database administration.

3.The database has a passsword for the internal login.

                                                        oracle server
                                                                  /    \
                                           Oracle database   oracle instance
                                                    /                       \
                              Physical database structure     Logical database structure
 

               (An oracle database's physical structure is datermined by the O.S files that constitute database)

Each oracle database is made of 3 types of files:

 - one or more datafile
 - 2 or  more redo log files
 - 1 or more control files
 

Oracle Instance
System global area(SGA) is an area of memory used for database admin. shared by the database servers.

The combinamtion of the background  process and memory buffers is called an instance.
 

                                            Oracle Instance
                                                /              \
                             User process       Oracle process
                                                            /               \
                                             server process         background process

A user process executes the code of an application program or an oracle tool.
Oracle process are server process and background process.
If the user and server process are on differrent computers of a network, if the user  process connect to hares server process thro' dispatcher process, the user process and  server process communicate thro' on using  SQL* NET.

* Normally tablespace is online than offline.

b)Schemas and Schema objects
* Schema is collection objects
* Schema objects are the logical structures that directly refer to the database's data.  Schema objects include structures as tables,views,sequence.
(There is no relationship between a tablespace and schema).
 1. table
 2.view - A view can also be thought of as a stored query.
 3.sequences
 4.program unit
 5.synonyms
 6.Index,cluster and hash clusters
 7.database link

Datablocks, Extents and segments
*one datablock corresponds to a specific number of bytes of physical database space  on disk.
*An extent is a specific number of continumous datablock obtained in a single allocation used to store a specific

Kiran

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