Why Become an Oracle Certified Professional?

The Oracle Certified Professional Program can give you a distinct advantage in an intensely competitive marketplace. By demonstrating a high level of competence using Oracle products, you will earn an industry-recognized, job role-related credential that can help distinguish you as a proven performer. Being an Oracle Certified Professional can help you gain more visibility and greater access to the industry's most challenging opportunities.

To obtain an OCP certification in database administration, you must past all five exams (in Japan, seven exams).  You do not have to take the tests in any particular order.  However, it is usually better to take the examinations in order because the knowledge tested builds from each exam.

If you're in Japan, Oracle Japan have pre-level OCP certification called Oracle Master Silver and Gold.  Upon passing seven exams, they'll certified you as Oracle Master Platinum in another word OCP.

Certification requirement in Japan and  in USA .
Basic information on Oracle Certification is available at:
http://www.oracle.com/tellmemore/?134077

In Japan
There are still Oracle7 certification track but it'll soon obsolete within a year.  I suggest you to concentrate on Oracle8 track. 
To archive Oracle Master Silver status, you need to pass following two test:

• 1Q0-005  SQL
  
• 1Q0-006  Introduction to Oracle