According to the type used at the button, the name varies.

For type="object", you need to define a method available at python and add it as name
def set_open(self,..)

For type="action", you need to specify which action you need to trigger,  It may be any action (window action, server action, etc..)
name="%(action_view_sale_advance_payment_inv)d"
E.g. https://github.com/odoo/odoo/blob/8.0/addons/sale/sale_view.xml#L87-L88

For type="workflow", this triggers the worklfow transition whose signal is equal to name