ER Diagram School Database

Question

I've made a ER Diagram using the Chen Notation and using a casus. Could anyone check if I'm doing it the right way?

Besides this I have some other questions:

Why does the weak entity always has one and one only? (thick arrow form assignments to has)

How do I process the salary between 20 times the scale and 35 times the scale in a ER Diagram?

I hope someone can help me

The ER Diagram I've made so far

http://imgur.com/ejIGO7S

Answer 1

ER diagram means Entity-Relationship diagram.
you can not write there about the process on Attributes.
you can do salary's scaling regarding a process in a query.