Consistency issues in real-time database systems

A consistency model is presented of real-time database systems that distinguishes the external data consistency from the internal data consistency as maintained by traditional systems, to provide a transaction schedule to meet deadlines. External consistency requires that the data used by a transaction reflect the current physical environment; this is in contrast to internal consistency, which presents a view consistent with the predefined constraints of the database. It is suggested that external consistency is preferable to internal consistency for many transactions. Operationally consistent schedules are defined that emphasize the operational effect of databases to the external world. A protocol that ensures the external consistency of transactions is presented