A classification of RE papers: Are we researching or designing RE techniques?

Discussion of a paper in RE program committees is often complicated by lack of agreement about evaluation criteria to be applied to the paper. For some years now, successive program chairs have attempted to increase clarity by including a paper classification in their CFP, and making the evaluation criteria per paper class explicit. This short note presents a paper classification based on this experience. It can be used as guide by program chairs. It can also be used by authors as well as reviewers to understand what kind of paper they are writing or reviewing, and what criteria should be applied in evaluating the paper.