If a normalized relation satisfies a set of dependencies, it has some redundancy. In relational database design such redundancy is removed by decomposition of a relation. Nested relation approach is another way to reduce such redundancy. Since all the facts are shown in one relation, this method is suitable for user interface. In order to get a proper nested relation, we must consider the form defined by the user as well as dependencies (in relational databases) or structures (in network databases). Thus we have to solve the following problems. (1) To check whether there is a contradiction between the user defined structure and the dependencies on the structure. (2) To find an efficient procedure to produce a nested relation when there is no contradiction. In this paper we will discuss the above two methods for relational and network databases.