Projects in OpenERP V5 Part 2

Code coming from the project module:

class project_work(osv.osv):

    _name = "project.task.work"

    _description = "Task Work"

    _columns = {

        'name': fields.char('Work summary', size=128),

        'date': fields.datetime('Date'),

        'task_id': fields.many2one('project.task', 'Task', ondelete='cascade', required=True),

        'hours': fields.float('Time Spent'),

        'user_id': fields.many2one('res.users', 'Done by', required=True),

    }

...

Using hours instead of a unit of measure and a value or defining in the application like in Tryton (http://www.tryton.org) what 1 day, 1 week, 1 month and 1 year of work means that your are obliged to encode hours in your time sheet...