Consider the following level - 0 dataflow diagram for a patient management system :
Consider the doctor entity, the system provides an appointment report to the doctor. If the system only generates the report upon a request from the doctor, do I must include an outgoing ( from the doctor entity ) dataflow labeled as for example "Appointment report request " ? or this dataflow is automatically understood implicitly from the diagram, so that not to make the diagram messy ?
The strange thing in this diagram is that it is a hospital where patients seemingly maintain all their own records, and where no information ever flows directly between the patient and the doctor. That's not consistent with my experience of using a hospital as a patient.
And whilst it is obvious that any real hospital must have a patient register and an appointment book, I'm sure real hospitals must be considerably more complicated than this, so it might pay not to introduce too much complexity (such as over billing data flows).
I'm also sensing confusion about the flows. Storage is obviously being represented at the granularity of a database table (or more abstractly, a document collection or book of entry). But I can't understand why making an appointment would cause the patient name to go into the patient register (whether for the first time, or as an update)?
I can understand why making an appointment causes data to be drawn out of the patient register (for example, getting a patient reference number), but I suspect you're using the patient name inwards to represent the fact that the name is necessary for looking up the reference number.
If my guess is correct, then that's not the correct approach, because you don't provide the name to the filing cabinet and then get a reference number provided by the filing cabinet in return, as if it's some kind of vending machine.
You already have the name, and you use that name to scan the files in the cabinet and get the reference number out. The data flow is one way - from filing cabinet to you, not from you to the filing cabinet. Nothing additional is stored in the filing cabinet - there is no flow from you (or anyone) to it, in this case.
More abstractly and without explicitly representing the operator of the information system (which may or may not be the patient, a clerical officer, or even the doctor), the flow is that the patient name, perhaps the doctor name, and desired appointment time comes from the patient, the reference number comes from the patient register, the doctor name might come from the patient medical record (if the patient doesn't explicitly say which doctor they need to see), the available appointment times come from the appointment book and go to the patient (for a decision), and what goes into the appointment book is a confirmed appointment time identifying the patient and doctor.
And there are obviously dynamics in this overall interaction that are not captured at the current level of granularity. For example, the patient is unlikely to state their desired time in final, until they have received information about the available appointments, but it's only implicit in my description that all items of information may not flow at once.
