Purchasing > Purchase Order > Cancel Line or Close?

Summary

What is the difference between Cancel Line and Close, and can either be done using a web service?

Content

In Fusion, if I navigate to Purchasing > Manage Orders, and query a Purchase Order, on the Purchase Order UI, in the Lines block, on the menu is Actions > Cancel Line, and Actions > Close. What is the difference between Cancel Line and Close?

I use PurchaseOrderService web service in Rel 8, and soon in Rel 9. Can I do Cancel Line or Close via web service?

 

Thanks!