The relational data model is defining records of data which are related to each other. The tables are identified using an entity relationship analysis which identifies the relationships between the table rows. In order to store data without redundancy in relational tables, the data model must be normalized. It is obvious that this paradigm can very easy be implemented using SGML/XML. This makes it easy to use SGML/XML as an archive as well as an exchange format for relational database applications. I will illustrate this in the following figure ().
relational data model
company emps emp emp-no="4321" name="Bernhard Weichel" adress="stuttgart"/ emp emp-no="12345" name="Helmut Gengenbach" adress="schwieberdingen"/ /emps depts dept name="K3/EES4" mgr="4321"/ dept name="FV/PLI" mgr="0815"/ /dept /company
But for engineering applications the relational model is not really appropriate. The information structure is very complex, so that normalization is a very high effort and ends up in an awful lot of links. SGML/XML's capabilities are far beyond the relational model.