Unformatted text preview: System Documentation Data Flow Diagrams Lecture 3 Agenda
What is a data flow diagram? What symbols are used in a data flow diagram? What are the types of data flow diagrams? What might data flow diagrams look like for the cash receipts process Documenting Systems: Data Flow Diagram (DFD)
A graphical representation of a system Depicts a system's components, data flows among components, and the sources, destinations, and storage of data Data Flow Diagram Symbols
Lecture Today Textboo k Types of DFD
Context DFD Physical DFD Logical DFD (Described in textbook) Example-Cash receipts process
A sales clerk scans customers' purchases into the register and collects the customers' payments. The computer uses the scanned data to update inventory records and sales data. Cash receipts and a register tape summarizing the sales data sent to the cashier. The cashier compares the cash and register tape with sales summary information generated by the computer. The cashier prepares a bank deposit slip, and the deposit is taken to the bank. Context DFD
Top-level DFD Least detailed Scope of system Shows process, sources and destinations of data and information Context DFD Physical DFD
Shows internal and external entities Shows flow of data in and out of these entities Shows where, how, and by whom but not exactly what is being accomplished (circles contain nouns) Physical DFD Logical DFD
Shows processes, data flow into and out of processes, and data stores Shows what is being done but not how, where, or by whom (circles contain verbs) Logical DFD--Level Zero Logical DFD
Each process on the level-zero DFD may be decomposed into more detailed processes Example: Decompose or subdivide 1.0, 2.0, 3.0, and 4.0 Balance must be maintained between levels Level-One DFD (Decompose process 4.0) Level-Two DFD, etc.
Decompose one of the processes in the level-one DFD Additional levels decompose one process in previous level Some Basic DFD Rules
A process must have inputs and outputs. Data must be moved by a process. Each data store must be involved with at least one process. Each data flow label should be unique because a process changes the data in some way. Comparing Flowcharts and DFDs ...
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- Fall '10
- Accounting, DFD Logical DFD