Conceptual Modeling Versus User Story Mapping - Which is the Best Approach to Agile Requirements Engineering?

User stories are primary requirements artifacts within agile methods. They are comprised of short sentences written in natural language expressing units of functionality for the to-be system. Despite their simple format, when modelers are faced with a set of user stories they might be having difficulty in sorting them, evaluating their redundancy, and assessing their relevancy in the effort to prioritize them. The present paper tests the ability of modelers to understand the requirements problem through a visual representation (named the Rationale Tree) which is a conceptual model and is built out of a user stories' set. The paper is built upon and extends previous work relating to the feasibility of generating such a representation out of a user stories' set by comparing the performance of the Rationale Tree with the User Story Mapping approach. This is achieved by performing a two-group quantitative comparative study. The identified comparative variables for each method were understandability, recognition of missing requirements/epics/themes, and adaptability. The Rational Tree was not easy to understand and did not perform as anticipated in assisting with the recognition of missing requirements/epics/themes. However, its employment allowed modelers to offer qualitative representations of a specific software problem. Overall, the present experiment evaluates whether a conceptual model could be a consistent solution towards the holistic comprehension of a software development problem within an agile setting, compared to more 'conventional' techniques used so far.