Schemas used during  Login into an EBS Application

When we sign on to Oracle E-Business Suite, we initially connect to the public schema,
APPLSYSPUB. Once the user name and password have been verified, Oracle E-Business
Suite connects you to the APPS schema and allows you to choose responsibility. You can
then use the Forms interface or HTML interface to access data that resides in a product
schema. So whenever a database session is created it will be connected via apps user.
The OAcore and forms services will be making the database session. In R12.2 the data source in Weblogic is used for the database connection.

More about APPLSYSPUB check the link below

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