There is no direct link between Organization Structure and access rights. In HR Configuration, we define employees of a company. Next, we create user accounts to give employees access to Odoo. We then link Employee to User in Employee form by using the menu Human Resources ‣ Employees.
Each user is then linked to groups which defines its access rights.
Now, we can control approval process using these groups.
For example, in order to allow only sales manager to approve quotations we can give-
<button name="quotation_approved" states="confirmed" type="object" string="Approve" class="oe_highlight" groups="base.group_sale_manager" />
Similarly, we can make fields, groups, page visible only to users of a particular groups by using ‘groups’ attribute
<field name="incoterm" widget="selection" groups="base.group_user"/>
<group name="sales_person" groups="base.group_user">
<page string="Other Information" groups="base.group_user">
So, this way groups can be used to limit access to directors, managers, users, etc. and approval process at various levels can be achieved.