The problem is that what joins to what differs depending on the context for what you are looking for. Sometimes you join an order to supplier, other times it w

The problem is that what joins to what differs depending on the context for what you are looking for. Sometimes you join an order to supplier, other times it will be to customer and other times it will be to a list of products. Sometimes, all of them need to be included. With nested structs the parent/child relationship is fixed. If your query needs to invert this relationship, you essentially have to search through your entire database which will be incredibly slow and resource intensive. Either that, or you just store your data and their relationships separately and then allow for highly optimised searches to be conducted between these relationships according to the query and statistics you hold about the data ... but then you have just reimplemented an RDBMS..