# File lib/tapkit/control/description.rb, line 225
                def validate_value( key, value )
                        if attr = @entity.attribute(key) then
                                attr.validate_value value
                        elsif relation = @entity.relationship(key) then
                                relation.validate_value value
                        else
                                msg    = "The '#{key}' property of #{@entity_name} is not found"
                                object = {key => value}
                                error  = ValidationError.new(msg, key, object)
                                raise error
                        end
                end