There is a class of database descriptions, involving one "acyclic" join dependency and a collection of functional dependencies, and nothing else, that appears powerful enough to describe most any real-world body of data in relational database terms. Further, this class has many desirable properties. Some properties make operations like updates and the selection of joins to implement a query over a universal relation especially easy. Other properties of interest were studied by other researchers who described the same class in radically different terms, and found desirable properties in their own contexts. It is the purpose of this paper to define the class formally, to give its important properties and the equivalences with the other classes mentioned, and to explain the importance of each property. This paper is intended to summarize the results that will appear in more detail in [FMU] and [BFMY].