Tables and Trees Don't Mix (very well)

There are principal differences between the relational model and XML's tree model. This causes problems in all cases where information from these two worlds has to be brought together. Using a few rules for mapping the incompatible aspects of the two models, it becomes easier to process data in systems which need to work with relational and tree data. The most important requirement for a good mapping is that the conceptual model is available and can thus be used for making mapping decisions.