A ‘fine grained’ entity bean is pretty much directly mapped to one relational table, in third normal form. A ‘coarse grained’ entity bean is larger and more complex, either because its attributes include values or lists from other tables, or because it ‘owns’ one or more sets of dependent objects. Note that the coarse grained bean might be mapped to a single table or flat file, but that single table is going to be pretty ugly, with data copied from other tables, repeated field groups, columns that are dependent on non-key fields, etc. Fine grained entities are generally considered a liability in large systems because they will tend to increase the load on several of the EJB server’s subsystems (there will be more objects exported through the distribution layer, more objects participating in transactions, more skeletons in memory, more EJB Objects in memory, etc.)
EJBDoclet is an open source JavaDoc doclet that generates a lot of the EJB related source files from custom JavaDoc comments tags embedded in the EJB source file.