What is the use of related fields in OpenERP?
related fields leads the control to another table the parent table wil have a onetomany relation with the child table and the child table have a manytoone relation towards the parent table.
eg: the account.invoice to account.invoice.line  with the following field
'invoice_line': fields.one2many('account.invoice.line', 'invoice_id', 'Invoice Lines', readonly=True, states={'draft':[('readonly',False)]}),
and account.invoice.line relates to account.invoice with the following code in reverse.
'invoice_id': fields.many2one('account.invoice', 'Invoice Reference', ondelete='cascade', select=True),
Can someone explain to me something about related fields. For example -

How it was used
How it can be helped
For which kind of scenario I should use fields.related

If anybody can provide a small example for real use of fields.related I would appreciate it.