Data Flow Diagram Help Needed

Hi,
is there a professional DB developer who could help me out.. on DFD for a doctors surgery.. i understand how a ERD is produced.. but im a little puzzled on DFD...

the entities i have in my DB which have been normalised to at least 2NF are as follows:

Appointments
Doctors
Drugs
Patient Consultation History
Patients
Pharmacy
Prescriptions


thankyou ever so much, for any accurate information!

The idea of a DFD is to show how data flows between different processes of a system.

A DFD has the following:

Data flows - This should be the name of the data which is flowing between two processes:

Code:

---

  appointment time
  -------------------->

---

External entities - These are entities which do not actually have a physical interaction with any of the systems processes. E.g. a patient

Code:

---

    +---------+   
  +          +
  |  patient  |
  +          +
    +---------+

---

Processes - An action which has input and an output such as booking an appointment.

Code:

---

+------------------+
|1|  Receptionist  |
|------------------|
| Book appointment |
|                  |
|                  |
+------------------+

---

Data stores - Such as a database or a filing cabinet. Thy should be labelled with a unique number. E.g. M1 for a manual data store, D1 for a digital datastore.

Code:

---

+-----------------------
| D1 | Patient Database
+-----------------------

---

You then join them all together to create a simple DFD:

Code:

---

    +---------+   
  +          +
  |  patient  |
  +          +
    +---------+
      |  ^
      |  |
      |D  |
      |O  |Appointment
      |B  |Card
      |  |
      |  |
      V  |
+------------------+
|1|  Recepionist  |    appointment time
|------------------|<--------------------------|
| Book appointment |                          |
|                  |--------------|            |
|                  |              |            |
+------------------+              |            |
      ^                          |patient    |
      |patient                    |name        |
      |details                    |            |
      |                          V            |
+----------------------- +---------------------------
| D1 | Patient Database  | D1 | Appointment Database
+----------------------- +---------------------------

---

The above is not the best example. You can have three types of DFD. Levels 0, 1, and 2 and possibly 3 depeending on the complexity of the system.

Level 0 just shows the dataflows of the external entities in and out of a system. The level 1 shows all the main processes and their dataflows and level 2 details more complex processes and breaks them down into further smaller processes.

I use MS Visio 2000 to create my DFD's and tend to steer clear of the ASCII art where possible. :lol:

First off, VisualAd did an excellent job of explaining DFD's (cheers mate:wave: )...I will just add one more tidbit....When I was going to school, I found these DFD's challenging - quite often my diagrams were not "Balanced". A balanced set of dfd's means that all inputs and outputs are shown at each level. So if you have an input with its respective output at level 0, and then you draw a level 1 diagram of that process and do not show the aformentioned data flow, your dfd is said to be unbalanced (lost a lot of marks over that!!!) all the best!!