How to populate different list boxes upon the choice of a certain selection

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Hi to All!

 

I am just wondering how can i achieve this goal:

 

Suppose i have a list box in which i have <b>programe names</b>.

And the programe name values are coming from a table.

 

Now whenever a <b>programe name</b> is selected, for example. <b>BBA</b> then a new list box should appear with a query from a table, with <b>no of semesters</b>.

 

Now when a <b>semester</b> is selected, for example. for the programe BBA, <b>8th</b> semester is selected, then a new list box should appear with a query from a table, with <b>subject names</b>

 

And in the last when the Insert Values button is clicked all values from the list boxes should in the table.

 

So summary is: 1 list box is dependent on another and the root list box is Programe Name.

 

Hierarchy of list boxes is :

Programe Name > No of Semesters > Subject Names

 

I am new to ajax, i have completed the 1st step i-e whenever a programe name is selected the no_of_semesters list box is appearing with values.

Now i am stucked and wondering how to move forward.....

 

Any idea! How can i accomplish this task? or Any code example from which i can take help?

 

Thanks in Advance.