3.1. Why Data Flow Diagrams?3.2. Data Flow Diagram Elements3.3. Basic Rules3.3.1. A Process Cannot Create Data3.3.2. Data Must Come from an Identified Source3.3.3. Data Cannot Move or Change by Itself3.3.4. A Diagram Must Begin and End with a Data Store or an External3.3.5. Processes Are Actions, Not Entities3.4. Summary and Detail Diagrams3.4.1. Do Not Go More Than Three Levels Deep3.5. About Creating Rough Diagrams3.6. Guidelines for Design Clarity3.6.1. Start at the Top and Flow Down and to the Left3.6.2. Align Everything3.6.3. Make Things the Same Size3.6.4. Distribute Elements Consistently3.6.5. Connect at Only Four Points3.6.6. Use Only Straight Lines and 90-Degree Angles3.6.7. Consider the Composition and Orientation3.6.8. Use the Same Font and Sizes3.6.9. Group Related Items and Annotate Diagrams to Add Meaning3.7. Other Types of Diagrams3.7.1. Architecture, Network, and Component Diagrams3.7.2. UML Diagrams3.7.3. Swim Lanes3.8. Summary