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

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

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

4. 4 CS451 - Lecture 6 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 systemData 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 Process: A data transformer (changes input to output) (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 graphData must always be processed in some way to achieve system function e.g., compute taxes, determine area, format report, display graph External Entity & Process

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

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

7. 7 CS451 - Lecture 6 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 user processingrequest videosource NTSC video signal digitalvideoprocessor requestedvideosignal monitor

8. 8 CS451 - Lecture 6 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

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

10. 10 CS451 - Lecture 6 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

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

12. 12 CS451 - Lecture 6 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

13. 13 CS451 - Lecture 6 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.

14. 14 CS451 - Lecture 6 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

15. 15 CS451 - Lecture 6 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

16. 16 CS451 - Lecture 6 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

17. 17 CS451 - Lecture 6 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

18. 18 CS451 - Lecture 6 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

19. 19 CS451 - Lecture 6 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

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

21. 21 CS451 - Lecture 6 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

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

23. 23 CS451 - Lecture 6 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