I just created a module using this code :

<record id="cym_form" model="ir.ui.view">
      <field name="name">CYM Tag</field>
      <field name="model">cym.tag</field>
      <field name="priority">1</field>
      <field name="arch" type="xml">
	<data><field name="cym_tag"/>
	<field name="modules" widget="one2many_tags"/>
      </data></field>
    </record>

And when I try to istall it I get this error :

ParseError: "Wrong value for ir.ui.view.type: 'data'" while parsing /home/production/odoo/addons/crm_cym/form_cym_view.xml:4

I really don't understand where it came from. Is it the use of wigdet ? The model ?

Here is my py code :

class ir_module(osv.osv):
    _inherit = 'ir.module.module'
    _columns = {
        'tag_id': fields.many2one('cym.tag', 'tag_name'),
    }

class cym_tag(osv.osv):
    _name = 'cym.tag'
    _order = 'name asc'

    _columns = {
        'tag_name': fields.char(u'Nom du Tag', size=128, required=True),
        'modules': fields.one2many('ir.module.module', 'tag_id', 'Modules'),
    }