Tools and Techniques for Requirements Engineering and Management - Requirements Engineering and Management for Software Development Projects - page 176

Fig. 13.2 Symbols used in ER diagrams

Fig. 13.3 Example of an entity-relationship diagram

13.2.11 Data Flow Diagrams

Dataflow diagrams are used to model the process of transforming the data by the
system. During the requirements phase, we model the existing system and during
design phase, we model the proposed system.
The symbols used in DFDs are shown in Fig. 13.4 . The symbol of the process
has many variants. I am depicting two of those variants.