OpenERP Inherited View

I need help in OpenERP, I want to add custom field for res.partner, I want to give them a category, and after I want to display this partners by choosing categories, how can I make this? I tried to make my inherited view but it says:

xml architect error.

from osv import fields,osv

class res_partner(osv.osv):

    _inherit = 'res.partner'

    _columns = {
           'mytext':fields.char('My custom text field',size=64),
    }

res_partner()