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Introduction to DFD

DFD Msys Introduction

Khim Batilo

on 25 March 2011

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Transcript of Introduction to DFD

Dataflow Diagram Dataflow Diagram Symbols Dataflow Diagram Levels Advantages of using DFD Creating a DFD
(Context Level) Common Mistakes in Creating DFD's Creating a DFD
(Level 0) Creating a DFD
(Child/ Level 1-Onwards) DFD (DataFlow Diagram)
Graphically characterize data processes and flows in a business system External Entities
Represent another department, a business, a person, or a machine
A source or destination of data, outside the boundaries of the system
Should be named with a noun
Data Flow
Shows movement of data from one point to another
Described with a noun
Arrowhead indicates the flow direction
Represents data about a person, place, or thing Process
Denotes a change in or transformation of data
Represents work being performed in the system
Process Naming Convention
Assign the name of the whole system when naming a high-level process
To name a major subsystem attach the word subsystem to the name
Use the form verb-adjective-noun for detailed processes Data Store
A depository for data that allows examination, addition, and retrieval of data
Named with a noun, describing the data
Data stores are usually given a unique reference number, such as D1, D2, D3
Represents a: Filing cabine, Database, or a Computerized file Freedom from committing to the technical implementation too early
Understanding of the interrelatedness of systems and subsystems
Communicating current system knowledge to users
Analysis of the proposed system
Context Level Level 0 Child (Level 1-Onwards) The highest level in a data flow diagram
The explosion of the context diagram
May include up to nine processes

Each process is numbered

Major data stores and all external entities are included

Data flow diagrams are built in layers
The top level is the Context level
Each process may explode to a lower level
The lower level diagram number is the same as the parent process number
Processes that do not create a child diagram are called primitive
Further explosion of level zero
Contains only one process, representing the entire system
The process is given the number 0
All external entities, as well as Major data flows are shown
Start with the data flow from an entity on the input side

Work backwards from an output data flow

Examine the data flow to or from a data store

Analyze a well-defined process

Take note of any fuzzy areas
Each process on diagram 0 may be exploded to create a child diagram
A child diagram cannot produce output or receive input that the parent process does not also produce or receive
The child process is given the same number as the parent process
Entities are usually not shown on the child diagrams below Diagram 0
If the parent process has data flow connecting to a data store, the child diagram may include the data store as well
When a process is not exploded, it is called a primitive process
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