
Information systems
combined into a single bubble for the level 1 DFD, and the bubbles
representing generating bills, which is a complex task, will be
expanded into several bubbles in a level 2 DFD.
Each bubble in the DFDs should be numbered, for ease of
reference. Level 1 bubbles are numbered simply 1, 2, 3, etc. If the
bubble labelled 1 is broken down into subsidiary bubbles in a level
2 DFD, these will be numbered 1.1, 1.2, 1.3, etc. If bubble 1.1 is
broken down into further subsidiary bubbles in a level 3 DFD,
these will be numbered 1.1.1,
1.1.2,
1.1.3, and so on.
Activity
Draw the first-cut DFD for the system you are modelling in the