User stories are useful for agile development methodologies for they are easy to learn and document. However, a list of user stories does not capture the underlying relations among the user stores, such as increase-customer-value relation between a functionality and its corresponding user interface. Goal models, on the other hand, quite capable of capturing several relations among requirements modelled as goals and help human experts answer questions such as 'how to achieve a requirement’ and ‘why does a certain requirement exist’.