CS451 Topic 6: DFD Tutorial

1. CS451Topic 6: DFD Tutorial Yugi Lee STB #555 (816) 235-5932 leeyu@umkc.edu www.sice.umkc.edu/~leeyu CS451 - Lecture 6

2. The Data Flow Model Every computer-based system is an information transform .... computer based system input output CS451 - Lecture 6

3. Data Flow Modeling Notation external entity process data flow data store CS451 - Lecture 6

4. External Entity & Process • External Entity: A producer or consumer of data • Data must always originate somewhere and must always be sent to something e.g., a person, a device, a sensor, computer-based system • Process: A data transformer • (changes input to output) • Data must always be processed in some way to achieve system function e.g., compute taxes, determine area, format report, display graph CS451 - Lecture 6

5. Data Flow Data flows through a system, beginning as input and be transformed into output. base compute triangle area area height CS451 - Lecture 6

6. Data Stores Data is often stored for later use. sensor # sensor #, type, location, age look-up sensor data report required type, location, age sensor number sensor data CS451 - Lecture 6

7. Constructing a DFD—I • review ERD to isolate data objects and grammatical parse to determine “operations) • determine external entities (producers and consumers of data • create a level 0 DFD processing request user requested video signal digital video processor monitor video source NTSC video signal CS451 - Lecture 6

8. Constructing a DFD—II • write a narrative describing the transform • parse to determine next level transforms • “balance” the flow to maintain data flow continuity • develop a level 1 DFD • use a 1:5 (approx.) expansion ratio CS451 - Lecture 6

9. The Data Flow Hierarchy a b P x y level 0 c p2 a f p1 b p4 d 5 g p3 e level 1 CS451 - Lecture 6

10. 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 CS451 - Lecture 6

11. Data Flow Diagrams (DFDs) (1) External Entity - source and destination of data • Advantages for systems view, working with users: (2) Process (3) Data Store (4) Data Flow CS451 - Lecture 6

12. Data Flow Diagrams (DFDs) • 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 CS451 - Lecture 6

13. 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. CS451 - Lecture 6

14. 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 CS451 - Lecture 6

15. 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 CS451 - Lecture 6

16. DFD Example: Step 2 (cont) 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 CS451 - Lecture 6

17. 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 CS451 - Lecture 6

18. DFD Example: Step 3 (cont) 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 CS451 - Lecture 6

19. 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 CS451 - Lecture 6

20. DFD Example: Step 5 FIFTH SENTENCE: Then the clerk enters the order data and saves it to the Daily Orders file. RESULT: CS451 - Lecture 6

21. DFD Example: Step 5 (cont) 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 CS451 - Lecture 6

22. DFD Example: Step 6 SIXTH SENTENCE: The clerk also prints an invoice and shipping list for each order, which are forwarded to Order Fulfillment. CS451 - Lecture 6

23. DFD Example: Step 6 (cont) 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 CS451 - Lecture 6