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So, not really sure if this is the right place for this but I have this current Context level data flow diagram for the bellow specification extract and I have never done one before so I was wondering if it was correct or if it needs fixing? any help appreciated

This is a link to a screen of my current one https://i.stack.imgur.com/gaIhN.png SPECIFICATION Currently the office staff operate the following processes:

Add/Amend/Delete Membership This is run on-demand when a new membership application is received or when a member indicates that he/she wishes to make amendments to their details. It is also run in those rare instances when a membership is terminated at the discretion of the manager. A new member has an ID number allocated (simply incremented from the previous membership accepted). A membership balance is also maintained for accounting purposes.

Another process operates in a similar fashion on data associated with transfer partners.

Monthly Maintenance This is run on the last day of each month to issue requests and reminders for subscriptions due, and to remove memberships where fees remain outstanding. Standard letters are also generated. Membership balances are updated as appropriate.

Payment Updates This is run prior to the Monthly Maintenance, with membership balances being updated accordingly.

Payments to partners are also disbursed at this time.

New Member Search This is run whenever a new member has been added to the database. The partners are partitioned in terms of vehicle category and location. Normally, there is a limited choice of partner in a particular location (if, indeed, there is any choice) but for some popular destinations, several partners are involved in providing the airport transfer. Thus, a search is then made through the appropriate section for potential matches in the following manner: A search is then made on the grounds of sex (many female passengers in particular prefer a driver of their own sex, especially if travelling alone or in couples). Matches are then selected according to factors such as cost (if available), availability of extra requested facilities (such as child seats, air-conditioning etc.)

Existing Member - Additional Searches These are run on-demand in the same fashion as for a new member's search. Members may of course request any number of such searches, but a separate payment is due for each.

All financial transactions (payments) are also posted to the separate Accounts file, which also stores other financial details relating to running costs for the consideration of the firm's accountants at the end of the financial year.

Thanks for any help, regarding this level 0 Context only DFD

TAM
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1 Answers1

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It needs some fixing.

The most obvious flaw is that you use verbs in your dataflows. In some cases this can be fixed easily by just discarding the verb. Return balance and status is not a datflow, but balance and status is.

In others cases it is not so easy. Check Balance, is it outstanding? sounds more like a Process than a dataflow. It looks like Accounting is responsible for doing that job. So will Accounting produce a list of outstanding balances? Or will it return a single balance and status, and if so, based on what input? Will your Airpot Transport System send a list of balances to check to Accounting?

Take for example Monthly Maintenance. What matters is that you want

  • requests and reminders for subscriptions due
  • Standard letters

These need to be visible in your DFD

The fact that you want to remove memberships where fees remain outstanding, probably has not place in the toplevel diagram, because that looks like an internal affair.

In general, focus on what the System produces. Maintaining internal state is secondary, is is a necessity to produce the desired output.

Martin Drautzburg
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