Video Transcript Excerpt
From Rigorous Physical Process Model (RPPM) to Context Diagram
At the very beginning of any IT project, one of the most important decisions that someone has to make is, "What are the boundaries of this project?" or, put differently, "What is the project scope?". With only the authority of the one wearing the BA hat, I cannot make a decision regarding the scope of the project. A project sponsor (the common title for the individual in the organization who is funding the project) or someone with similar authority has to define the project scope. To assist the decision maker in the scope discussion, a Rigorous Physical Process Model (RPPM) showing the movement of materials and data through an organization is a fantastic tool.
Because "scope creep" is a significant risk on IT projects, we not only need someone with the proper authority to define the scope, we have to represent their decision in a form that everyone involved with the project can visualize, understand, and defend. One of the simplest tools for visualizing project scope is a Context-level Data Flow Diagram (DFD). Beyond making the project scope visible, a DFD will ultimately allow us to discover, analyze, and represent functional and non-functional requirements.
Once we know the project scope, it is really easy to convert an RPPM to a Context-level DFD – we just need to make some minor adjustments. Circles on an RPPM represent people or places so they naturally have a noun name. Circles on a DFD, however, represent PROCESSES which have a VERB/OBJECT name (do something to something) and are in scope for our project! People or places that are out of scope for our project are EXTERNAL ENTITIES represented by a square with a NOUN name on a DFD. This distinction is what makes the project scope stand out on a Context-Level DFD.
… [end of excerpt]