DBOW is a database compiler-compiler or front-end. It takes table definitions in a relatively high-level language and prepares C, C++, PHP, Perl (etc) functions for manipulating the database. It will also produce SQL table data for MySQL.
SAPRFC is the extension module for PHP4 and PHP5 that allow call ABAP functions in an SAP R/3 system from PHP scripts. On other side it's also possible write RFC server program in PHP and callPHP functions from ABAP.