DFD Construction Process

1. DFD Construction Process Words to Diagrams

2. Data Flow Diagrams (DFDs) • Analysis tool • System modeling • Excellent documentation tool • Data flow, aka, business process • Provide a way to see the pattern • Systems Thinking • Systems View • Systems Approach

3. Data Flow Diagrams (DFDs) - continued • Advantages for systems view, working with users: • Four simple symbols:

4. Data Flow Diagrams (DFDs) - continued • Simple rule: • left to right, top to bottom, basically (like English) • Show all processes • data flows must start or end in a process • beware of black holes - every process and data store must produce data • no “magic processes” - must enter all needed data to get data out

5. Data Flow Diagrams (DFDs) - continued * Key: Simple Symbols Most common error: Trying to do too much

6. DFD Example In the following example, a DFD will be created based on a paragraph about Bebop Records Co.’s method of receiving and filling orders. In this example, the information necessary to create the DFD is provided for us. In Real Life, this information comes from extensive interviewing, document gathering, and other research. Depending upon the system being studied, the number of people working on it, etc., the development of a detailed DFD can take anywhere from a few hours to several months (paid for by your client with NO CODE TO SHOW FOR IT). Yet it is a very standard and meaningful part of system documentation.

7. DFD Example Bebop Records is a mail-order company that distributes CDs and tapes at discount price to record-club members. When an order processing clerk receives an order form, he or she verifies that the sender is a club member by checking the Member file. If the sender is not a member, the clerk returns the order along with a membership application form. If the customer is a member, the clerk verifies the order item data by checking the Item file. Then the clerk enters the order data and saves it to the Daily Orders file. The clerk also prints an invoice and shipping list for each order, which are forwarded to Order Fulfillment.

8. DFD Example - Step 1 FIRST SENTENCE: Bebop Records is a mail-order company that distributes CDs and tapes at discount price to record-club members. RESULT: initial title Bebop Records

9. DFD Example - Step 2 SECOND SENTENCE: When an order processing clerk receives an order form, he or she verifies that the sender is a club member by checking the Member file. RESULT: Bebop Records Order Processing

10. DFD Example - Step 2 continued SECOND SENTENCE: When an order processing clerk receives an order form, he or she verifies that the sender is a club member by checking the Member file. RULES FOLLOWED: • left to right, top to bottom • data flows start or end in a process

11. DFD Example - Step 3 THIRD SENTENCE: If the sender is not a member, the clerk returns the order along with a membership application form. RESULT: Bebop Records Order Processing

12. DFD Example - Step 3 continued THIRD SENTENCE: If the sender is not a member, the clerk returns the order along with a membership application form. RULES FOLLOWED: • shows all processes without conditions

13. DFD Example - Step 4 FOURTH SENTENCE: If the customer is a member, the clerk verifies the order item data by checking the Item file. RESULT: Bebop Records Order Processing

14. DFD Example - Step 4 continued FOURTH SENTENCE: If the customer is a member, the clerk verifies the order item data by checking the Item file. RULES FOLLOWED: • left to right, top to bottom • data flows start or end in a process • shows all processes without conditions

15. DFD Example - Step 5 FIFTH SENTENCE: Then the clerk enters the order data and saves it to the Daily Orders file. RESULT:

16. DFD Example - Step 5 continued RESULT: Bebop Records Order Processing

17. DFD Example - Step 5 continued FIFTH SENTENCE: Then the clerk enters the order data and saves it to the Daily Orders file. RULES FOLLOWED: • left to right, top to bottom • data flows start or end in a process

18. DFD Example - Step 6 SIXTH SENTENCE: The clerk also prints an invoice and shipping list for each order, which are forwarded to Order Fulfillment. RESULT:

19. DFD Example - Step 6 continued RESULT: Bebop Records Order Processing

20. DFD Example - Step 6 continued SIXTH SENTENCE: The clerk also prints an invoice and shipping list for each order, which are forwarded to Order Fulfillment. RULES FOLLOWED: • left to right, top to bottom • data flows start or end in a process • shows all processes without conditions • beware of black holes - every process and data store must produce data

21. Individual Homework Assignment All Villanova students have gone through the admission process in order to become an enrolled member of the student body. As you think back on the admissions “process” there was a variety of information that was required in order to accept you as a student. For this assignment, you are to create a context diagram and a 1st level decomposition of the admission process. Be sure you understand the “system boundary”, use proper symbols, and represent all of the information needed by the admissions department. The Admissions web site is a good place to start if you don’t remember everything you did when you applied. http://www.villanova.edu/enroll/admission/