Comparing Two Different Approaches to Products in Abstract Relation Algebra

During the development of relation algebra as a formal programming tool, the need of some form of “categorical product” of relations became apparent, whether as a type or as an operation. Two approaches arose in the late 70’s and the early 80’s which will be referred here as the “Munich approach” (see, e.g., [18, 7]) and the “Rio approach” (see, e.g., [13, 12, 22]).