I have been using Yourdon's context level data flow diagram for about 15 years. I still find it one of the best tools for scoping project boundaries and getting everyone on the team to see the project in the same way. The only complaint that I have received about this diagram from my business stakeholders is that they want to know which business processes are going to be included in the project. Understanding the diagram gives you this information, but people who don't use the diagram frequently may feel it is missing a piece.
Because of this communication problem, we list the high-level business processes that are inside the project, right on the diagram. This gives the business stakeholders an explicit scope that they can review and approve. These high-level processes (usuallly about 5) give Business Analysts the starting point for detailed requirements gathering in the same way that the dataflow arrows and external agents do.
Once you understand a particular tool or technique, you can begin to modify it to better suit your audience. Our ultimate goal is clear communication, whatever technique we use.
