Conditions of efficient updates on network structures

Redundant network structures allow efficient retrievals. Procedures to design network structures that allow efficient retrievals (9) add redundancies into network structures. However, as redundancies increase, costs of updates increase. When network structures are redundant, costs of updates include costs of updating original data, checking consistencies and updating derived data. In this paper, we present the super-key condition to reduce costs of checking consistencies in redundant network structures. First, we present constraints required to keep redundant network structures consistent and show a sequence of processes to delete or insert a record in redundant network structures keeping the constraints. Then, Relationships between functional dependencies and updates are discussed to derive the super-key condition. The condition classifies network structures regarding costs of the processes to delete or insert a record. Finally, we give a procedure to design network structures that satisfy the super-key condition. The procedure may increase redundancies of network structures to reduce costs of updates.