
Ideally, in terms of the three-level DBMS architecture discussed in Chapter 2,
the first-level design would correspond closely to the conceptual schema, whereas the
second-level design would be a step along the road towards internal schema
design. This presupposes a DBMS which is clever enough to map an external schema
via the conceptual schema into an internal schema, where each type of schema may
have a markedly different view of the data (in the way that Fig. 15.2 differs from
Fig. 14.2, for example). Few, if any, commercially available DBMS are capable of this
degree of sophistication, so it may be more realistic to view the first-level design ...