In order to obtain the Java EE 6 Web Component Developer Certified Expert certification, you need to:
1) have a prior Java Programmer certification
2) pass exam 1Z0-899
I'm not sure what your question is about 501 and 803. We don't have an exam - 1Z0-501. If you do not already have a Java Programmer Professional certification, you'll need to start there. In order to get the Java SE 7 Programmer Certified Professional certification, you'll need to pass exams 803 and 804. Then you will move on to 899 for the Web Component Developer certification.
Certification Forum Moderator