c program against databases

hello, i would like to write a unix-based c program that would perform SELECT and INSERT against a database. i am very familiar with esql/c. however, i would like to productize this program and allow it to work with a variety of databases (Informix, Oracle, Sybase, DB2) on a variety of operating systems (variations of unix and NT, maybe). is the best way to write embedded sql c code (and recompile using esql/c, pro*c, etc...)? how standard is this? is there a good toolkit to help me out? is there a good book or website to learn more? how do app dev packages like IEF do it? it seems like i would have to buy alot of precompilers. for example, 4 databases running on 5 platforms would require 20 (4 x 5) esql/c like compilers. is this true? i would appreciate any guidance. Lan H. Tran Ventera Corporation lantran@ventera.com