Business process modelling has been given great attention due to its crucial role in developing computer-based systems that support (and automate) organizational processes. In information systems; building the right process architecture is vital, since a poor division of organizational processes can lead to complex designs or incoherent structure. Moreover, process architecture acts as a "big picture" of what the organization does, and represents dynamic relationships between the existing processes, which in turn helps understand how the organization works (Ould, 2005). A number of process architecture methods are available, however, few studies focused on assessing these methods, and comparing some of them to find out how easy they are to be used in particular contexts, and whether they can be standardized. In a previous work for the author, ARIS was used to generate a process architecture diagram for academic libraries (Tbaishat, 2015). This paper discusses the derivation of a Process Architecture Diagram (PAD) using Riva method in detail; in contrast to the process architecture diagram developed using ARIS. The information system selected as an example for this comparative study is in the context of academic libraries, embedding various –generic - library processes. ARIS is more professional tool that can be used to support large organizational systems with clear division of processes, many users and less complicated architecture. The translation from ARIS process architecture to Riva's PAD is not likely to be straightforward, since there are major differences between the two methods, and it will rely on the analyst's ability of interpretation.