“…In most cases the storage layer is implemented by a general database management system. Relational (e.g., [12,8,3,5]), objectoriented (e.g., [17,18]) and XML databases (e.g., [8,3,5,17,18]) have all been observed in the concrete BP Model Repositories that were studied. Alternative implementations that have been observed are implementations using general repositories, of which one using a distributed repository, and an implementation in which the data is stored as files in a filesystem.…”