Trying the following code:

from openerp import models, fields

class SomeClass(models.Model):
    _inherit = 'sale.order'

    description = fields.Char(default="Some text")

Getting the following error:

2014-10-07 12:37:19,054 22276 ERROR sandbox werkzeug: Error on request:
Traceback (most recent call last):
  File "/usr/share/pyshared/werkzeug/serving.py", line 159, in run_wsgi
    execute(app)
  File "/usr/share/pyshared/werkzeug/serving.py", line 146, in execute
    application_iter = app(environ, start_response)
  File "/usr/lib/python2.7/dist-packages/openerp/service/server.py", line 280, in app
    return self.app(e, s)
  File "/usr/lib/python2.7/dist-packages/openerp/service/wsgi_server.py", line 216, in application
    return application_unproxied(environ, start_response)
  File "/usr/lib/python2.7/dist-packages/openerp/service/wsgi_server.py", line 202, in application_unproxied
    result = handler(environ, start_response)
  File "/usr/lib/python2.7/dist-packages/openerp/http.py", line 1215, in __call__
    return self.dispatch(environ, start_response)
  File "/usr/lib/python2.7/dist-packages/openerp/http.py", line 1189, in __call__
    return self.app(environ, start_wrapped)
  File "/usr/share/pyshared/werkzeug/wsgi.py", line 411, in __call__
    return self.app(environ, start_response)
  File "/usr/lib/python2.7/dist-packages/openerp/http.py", line 1347, in dispatch
    ir_http = request.registry['ir.http']
  File "/usr/lib/python2.7/dist-packages/openerp/http.py", line 319, in registry
    return openerp.modules.registry.RegistryManager.get(self.db) if self.db else None
  File "/usr/lib/python2.7/dist-packages/openerp/modules/registry.py", line 293, in get
    update_module)
  File "/usr/lib/python2.7/dist-packages/openerp/modules/registry.py", line 324, in new
    openerp.modules.load_modules(registry._db, force_demo, status, update_module)
  File "/usr/lib/python2.7/dist-packages/openerp/modules/loading.py", line 354, in load_modules
    force, status, report, loaded_modules, update_module)
  File "/usr/lib/python2.7/dist-packages/openerp/modules/loading.py", line 263, in load_marked_modules
    loaded, processed = load_module_graph(cr, graph, progressdict, report=report, skip_modules=loaded_modules, perform_checks=perform_checks)
  File "/usr/lib/python2.7/dist-packages/openerp/modules/loading.py", line 158, in load_module_graph
    models = registry.load(cr, package)
  File "/usr/lib/python2.7/dist-packages/openerp/modules/registry.py", line 147, in load
    model = cls._build_model(self, cr)
  File "/usr/lib/python2.7/dist-packages/openerp/models.py", line 585, in _build_model
    original_module = pool[name]._original_module if name in parents else cls._module
  File "/usr/lib/python2.7/dist-packages/openerp/modules/registry.py", line 100, in __getitem__
    return self.models[model_name]
KeyError: 'sale.order'

Changing the code to:

from openerp import models, fields

class SomeClass(models.Model):
    _inherit = 'res.partner'

    description = fields.Char(default="Some text")

... and everything goes with no errors.

What is the correct way to inherit from SalesOrder in Odoo v8?
Need to add some fields to the base model.