System Analysis and Design. Data Flow Diagram. System Analysis and Design

Transcription

1 Data Flow Diagram 1

2 Data Flow diagram The dataflow diagram is a modeling tool that allows us to picture a system as a network of functional processes, connected to one another by pipelines and holding tanks of data 2

3 Context Diagrams Data Flow Diagrams Top-level view of an information system that shows the system s boundaries and scope Do not show any data stores in a context diagram because data stores are internal to the system. Begin by reviewing the system requirements to identify all external data sources and destinations 3

4 Context Diagrams Record the name of the entities and the name and content of the data flows, and the direction of the data flows. What makes one system more complex than another is the number of components, the number of levels, and the degree of interaction among its processes, entities, data stores, and data flows 4

5 Context Diagrams Shows the overall business process as just one process. The process is given the number zero. Shows all the outside entities that receive information from or contribute information to the system Slide 5

6 Context Diagrams 1. Each context diagram must fit on one page. 2. The process name in the context diagram should be the name of the information system. 3. Use unique names within each set of symbols. 4. Do not cross lines. 5. Use a unique reference number for each process symbol. 6

7 Developing DFDs 1. Context Diagram for Pizza Hut food ordering system 0 CUSTOMER Customer Order Food Ordering System Food Order KITCHEN Receipt Management Reports 7 RESTAURANT MANAGER

8 Creating a Set of DFDs Create a graphical model of the information system based on your factfinding results Performing three main tasks Step 1: Draw a context diagram Step 2: Draw a diagram 0 DFD Step 3: Draw the lower-level diagrams 8

9 Creating a Set of DFDs Draw a Diagram 0 DFD Diagram 0 Zooms in on the context diagram and shows major processes, data flows, and data stores Must retain all the connections that flow into and out of process 0 Each process has a reference number Diverging data flow 9

10 Creating a Set of DFDs Draw the Lower-Level Diagrams Must use leveling and balancing techniques Leveling Uses a series of increasingly detailed DFDs to describe an information system Exploding, partitioning, or decomposing 10

11 Data Flow Diagrams Lower-Level Diagrams Balancing Ensures that the input and output data flows of the parent DFD are maintained on the child DFD

12 Developing DFDs 1. Context Diagram for Pizza Hut food ordering system 0 CUSTOMER Customer Order Food Ordering System Food Order KITCHEN Receipt Management Reports 12 RESTAURANT MANAGER

13 Developing DFDs 2. Level-0 Diagram for Pizza Hut food ordering system CUSTOMER Customer Order Receipt 1.0 Receive & Transform Customer Food Order Food Order KITCHEN 2.0 Update Goods Sold File Goods Sold Inventory Data 3.0 Update Inventory File D2 13 Goods Sold File Formatted Goods Sold Data Daily Goods Sold Amounts 4.0 Produce Management Formatted Inventory Data System Analysis Report and Design D1 Daily Inventory Depletion Amounts Management Reports Inventory File manager

14 Developing DFDs 2. Level-1 Diagram for Pizza Hut food ordering system Customer Order 1.1 Receive Customer Order Customer Order 1.3 Transform Order to Kitchen Format Food Order Customer Order Customer Order Customer Order 1.5 Generate Inventory Decrements Inventory Data Receipt Generate Customer Receipt 1.4 Generate Goods Sold Increments Goods Sold Data

15 Rules Governing Data Flow Diagramming 15

16 Rules Governing Data Flow Diagramming Process Rule 1: Process cannot have outputs only. It means it is making data from nothing Only a source should have outputs without inputs 16

17 Rules Governing Data Flow Diagramming Process Rule 2: No Process can have only inputs If an object has only inputs, then it must be a sink. 17

18 Rules Governing Data Flow Diagramming Process Rule 3: A Process should have a verb phrase label Generate Orders 18

19 Rules Governing Data Flow Diagramming Process Rule 4: Data cannot move directly from one data store to another data store. Data must be moved by a process Generate Orders 19

20 Rules Governing Data Flow Diagramming Process Rule 5: Data cannot move directly from an outside source to a data store Data must be moved by a process which receives data from the source and places the data into the data store Source Source Generate Orders 20

21 Rules Governing Data Flow Diagramming Process Rule 6: Data cannot move directly to an outside sink from a data store Data must be moved by a process Sink Generate Orders Sink 21

22 Rules Governing Data Flow Diagramming Process Rule 7: A data store has a noun phrase label Inventory 22

23 Rules Governing Data Flow Diagramming Process Rule 8: A data store A data store must have at least one incoming and one outgoing data flow. Inventory 23

24 Rules Governing Data Flow Diagramming Process Source/Sink Rule 9: Data cannot move directly from a source to a sink It must be moved by a process Generate Source Sink Source Sink Orders 24

25 Rules Governing Data Flow Source/Sink Diagramming Process Rule 10: A source/sink has a noun phrase Supplier 25

26 Rules Governing Data Flow Diagramming Process Data flow Rule 11: A data flow has only one direction of flow between symbols It may have both direction flows between a process and a data store to show a read before an update Later it is indicated by two separate arrows 26 Generate Orders Generate Orders

27 Data flow Rules Governing Data Flow Diagramming Process Rule 12: A fork in a data flow means that exactly the same data goes from a common location to two or more different processes, data stores, or sources/sinks. There should not be a variation in duplication A A 27 B A

28 Rules Governing Data Flow Diagramming Process Data flow Rule 13: A joint in a data flow means that exactly the same data comes from any of two or more different processes, data stores, or sources/sink to a common location Only similar data flows can be joined A A B A 28

29 Rules Governing Data Flow Diagramming Process Data flow Rule 14: A data flow cannot go directly to the same process it leaves. There must be at least one other process which handles the data flow, produces some other data flow, and returns the original data flow to the beginning process A B 29 A C A

30 Rules Governing Data Flow Diagramming Process Data flow Rule 15: A data flow to a data store means update (delete or change) Generate Orders Delete or changed data 30

31 Data flow Rules Governing Data Flow Diagramming Process Rule 16: A data flow from a data store means retrieve or use Generate Orders Retrieve/Use 31

32 Data flow Rules Governing Data Flow Diagramming Process Rule 17: A data flow must have a noun phase label Updated stock 32

33 DFDs Exercises 33

34 Data Flow Diagrams Examples of correct uses of data store symbols in a data flow diagram. [1] 34

35 Data Flow Diagrams 35

36 Data Flow Diagrams Entity can be connected with a process only Examples of correct uses of external entities in a data flow diagram.[1] 36

37 Data Flow Diagrams 37

38 Data Flow Diagrams 38

39 DFD Errors 39

40 DFD Errors 40