Data Dictionary and Internet & Databases

Hi all ! I need help in theory of Databases. I need to details about Data Dictionary.
My Questions are about Data Dictionary:
1. Role and Importance of Data Dictionary in DBMS structure ?
2. What are the various types contents available in the data dictionary?

My Second topic is Internet and Databases.
my Question is:
1.Role of databases in Internet
2.What are various tools available for managing databases in internet

Hoping for some Good answers and with tutorials.

Thanks.

 

No one has replied yet to my questions. So,I have decided to answer these on my own some time