A database is identified by a Global Database Name, and the instance associated with the database is identified by an Oracle System Identifier (SID)
Global Database Name - It is the name given to a database to uniquely identify it from the other databases in a network. The Global Database Name consists of two components: a database name and a domain. It is represented as follows: database_name.domain.
where:
database_name is the name of the database. It can contain thirty characters as long as it's 8-character unique. (alphanumeric, underscore (_), dollar ($), and pound (#)).
domain is the computer environment used for the database. It should contain no more than 128 characters (alphanumeric, underscore (_), and pound (#)), inclusive of all periods.
For example:
sales.us.example.com
where:
database_name is sales
domain is us.example.com
Oracle System Identifier - It is a unique name for an Oracle database instance on a specific host. The Oracle System Identifier (SID) helps in identifying the control file, and locating the files required to open the database. When you enter the Global Database Name, Oracle Universal Installer automatically populates the Oracle System Identifier field with the database name. You can change this name in Advanced installation.
Oracle Univeral Installer limits the SID to 12 alphanumeric characters for single instance databases. For RAC databases, the SID prefix, which is the first 8 characters of the SID, must be a unique name for each database. The SID prefix cannot contain underscore (_), dollar ( $), or pound (#).
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