User Processes
When a user runs an Oracle tool Oracle creates a user process to run the user's application. A database user who needs to request information from the database must first make a connection with the Oracle server. The connection is requested using a database interface tool, such as SQL*Plus, and beginning the user process. The user process does not interact directly with the Oracle server. Rather it generates calls through the user program interface (UPI), which creates a session and starts a server process
Connections and Sessions
The terms "connection" and "session" are closely related to the term "user process", but are very different in meaning.
A connection is a communication pathway between a user process and an Oracle instance. A communication pathway is established using available interprocess communication mechanisms (on a computer that executes both the user process and Oracle) or network software (when different computers execute the database application and Oracle, and communicate via a network).
A session is a specific connection of a user to an Oracle instance via a user process. For example, when a user starts SQL*Plus, the user must provide a valid username and password and then a session is established for that user. A session lasts from the time the user connects until the time the user disconnects or exits the database application.
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