Navigation and schema transformations for producing nested relations from networks

Efficient procedures for producing nested relations from networks are considered. Various types of nested relations are defined according to the interaction between the networks' and nested relations' schemas. Among these types, partitioned normal form (PNF) and accordant nested relations are shown to be produced by an extended navigation, called touch information display (TID) navigation, which requires time proportional to the number of tuples in the relation. It is demonstrated that a network can effectively produce a variety of nested relations by navigation. The efficiency of production is classified according to the interaction between the schemas of networks and targets. Non-PNF and/or non-accordant targets are generated using duplicate depletion. On the other hand, PNF and accordant targets can be generated using only navigation, which requires linear time in the number of tuples in the relation. Furthermore, for the cases on non-PNF and non-accordant targets, the TID method exploits the existence of links, so that the size of the region of the subrelation upon which deletion of duplicated values should be performed is limited.