Need help with (3) The Null approach

[15 PointsConsider an E/R diagram which includes entity sets F, G, H, with the attributes (c,d}, {e}, and {g,h}, respectively. The underlined attributes indicate the keys. In this diagram we also have a relationship S between G and H, which has f as its own attribute. There exists also a weak entity set E with the attributes {a,b}. Furthermore, the entity set G is connected to E via an isa relationship. Finally, the diagram includes a many-to-one, weak relationship R from E to F indicated with a rounded arrow to F. Convert this diagram into a relational database schema using (1) the E/R style, (2) the OO approach, and (3) the null approach. In each case, show the relations we get and underline the key attributes