In a multi-user environment, there can be SITUATIONS when one or more users are reading certain set of data while other is modifying the same set of data. Data consistency provides a stable or CONSISTENT data to the users throughout the session.
Data consistency is maintained through rollback segments. A rollback SEGMENT holds the data image before CHANGE; therefore, one or more sessions will get the same image of the data throughout the session that were reading the data while another session is updating.

In a multi-user environment, there can be situations when one or more users are reading certain set of data while other is modifying the same set of data. Data consistency provides a stable or consistent data to the users throughout the session.
Data consistency is maintained through rollback segments. A rollback segment holds the data image before change; therefore, one or more sessions will get the same image of the data throughout the session that were reading the data while another session is updating.