A logical representation of a database, which is the way a database is presented to clients. A database can be presented as multiple services and a service can be implemented as multiple database instances. The service name is a string that is the global database name, that is, a name comprised of the database name and domain name, entered during installation or database creation. If you are not sure what the global database name is, you can obtain it from the combined values of the SERVICE_NAMES parameter in the initialization parameter file.
Connect descriptors used by clients to connect to an Oracle9i or Oracle8i database should be configured with the SERVICE_NAME (without an S) parameter.
Database Identification by Service Name Rather than SID
Oracle Net Services Configuration Overview
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