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.
1 is the numbering default value. You can modify this value at any time and type an integer greater than 0 in the process or data store property sheet.
All the objects (processes or data stores) you will create afterwards will be automatically numbered in ascending order. Number ID of the already created objects will not be impacted unless you use the Renumber Process IDs command or the Renumber Data Store IDs command by right-clicking the diagram background.
This feature reorders objects number IDs and the object number ID you have changed become the last in the ascending order.
In addition, numbers are used in leveled data flow diagrams. You can decompose a process into lower level processes, which more closely analyze the various transformations carried out by the parent process. The numbering feature allows child processes to inherit the number ID of their parent process.
So 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:
For more information about decomposed processes, see Decomposing Processes.
Data store numbering is only available with Gane & Sarson methodology.