In idempiere,when i click on a New Record button in a tab, which function is get executed? Which function calls update_sequences() sql function?

Question

I'm new to idempiere and i want to know following

1. When i click on a New Record button in a tab, which function is get executed? for example, In sales order window, in Order tab, when I click on the New Record, it get a new page where Document no is already filled in. I found out that ad_sequence table contain all the sequence data which contains a column currentnext. Which function query the ad_sequence table and get the currentnext value?
2. I found that there is a sql function update_sequences(). Which function calls update_sequences() sql function after I saving a record?

Thank you.