If we consider that Context diagram is the diagram that describe the system as a single process and level 0 diagram is the one that decomposes this main process into major process and so on. I am mentioning this because my text books refer to context diagram as level 0 diagram. However , in my course context diagram is different from level 0 diagram . Now, my question is does data stores can appear in level 1 diagram ? because in all the level 1 diagrams I saw is that they doesn’t have data stores . Only data stores appears in level 0 diagram .