Process and data store numbering is a convenient way of referencing processes and data stores in a DFD. For example, in a lively discussion about processes or data stores in a DFD it is easier to mention a process or a data store by its number instead of its name, which can sometimes be long or complex. Data store numbering is only available when using the Gane & Sarson methodology.
Numbering starts, by default, at 1, but you can modify this value at any time by entering an integer greater than 0 in the process or data store property sheet. All the objects (processes or data stores) created afterwards are numbered in ascending order, but the Number ID of previously created objects are not updated unless you right-click the diagram background and select Renumber Process IDs or Renumber Data Store IDs.
Numbering can be used in leveled data flow diagrams, where you decompose a process into lower level processes, to more closely analyze the various transformations carried out by the parent process (see Decomposing Processes). Child processes inherit the number ID of their parent process, so that, for example, a top level DFD would have processes 1 2 3 4, the sub-process of process 3 would have processes 3.1, 3.2, 3.3, and 3.4, and the sub-process of the sub-process 3. 2 would have components 3.2.1, 3.2.2, 3.2.3, and 3.2.4:
