Non first normal form relations and recursive queries: An SQL-based approach

The work presented in this paper is an attempt to combine two different but closely related research areas in the data base field, namely the quite heavily investigated question of recursive queries in relational data bases on the one hand and the introduction of non first normal form relations on the other. This paper proposes the integration of recursive queries and non first normal form relations by providing a recursion mechanism which can be nested according to the structure of a non first normal form relation. It is shown by examples that this method can be used to formulate queries which are rather cumbersome if only flat relations are used. Especially, in some cases the problem of performing a selection on a recursively defined relation disappears. This question has been the topic of several research papers recently. Moreover, many queries can be formulated in a more natural way than in the world of flat tuples. Therefore, nested recursive queries in combination with non first normal form relations provide a contribution to the problem of modelling complex data.