>Hello Friends,
>
>Is there any way by which i can create multiple databases in oracle within the same oracle instance.
>
>Or is this feature is achieved through tablespace concept.

Usually, all databases are created under the same Oracle instance. Only the schema changes for each one. For example, we create a new user and give it a name representative of the particular app being developed [e.g., using your company name, create a user/schema called ACME]. Then all the tables, views, sequences, triggers, procedures and functions are created under that user name. When I create a primary key on a table I name the PK something like PK_ACME_AbbreviatedTableName_FieldName. I do the same for other objects except tables and views.

I do create a new tablespace for each application. I use a generic tablespace [used by all users/schemas] for all Indexes.