Transcript Data Flow Diagram - High Point University

Data Flow Diagram
• Purpose – visually depict how data moves
and changes through a top-down, logical
model
• Logical model – requirements and the
relationship among the requirements
• DFD is not program logic or processing
logic
Data Flow Diagram
Data Flow Diagram
• Leveling
– Top-down approach
– General to detailed
DFD Process Symbol
• Processes change the data from one form to
another form
• Data is input for a process
• Processes transform data to produce output
DFD Process Symbol Rules
• Place the name of the process inside the
circle in ALL CAPS
• The name identifies its function
• The name consists of an active verb
followed by a descriptive, single noun
APPLY DISCOUNT
VERIFY ORDER
DFD Process Symbol Rules
• Process details are not shown
• A process is a black box, as for as details
are concerned
• Levels of DFD (context / diagram 0)
DFD Data Flow Symbol
• A line with an arrowhead showing the
direction of the data flow.
• Purpose is to depict the pathway that data
moves from one part of an information
system to another part
• Data Flow name identifies the data it represents
DFD Data Flow Symbol
• The name consists of adjectives and a
singular noun
• The line can be straight or curved
• Each data flow equals a specific piece of
data or a set of data (student name or class
roster)
BANK DEPOSIT
STUDENT GRADE
DFD Data Flow Symbol
• At least one data flow must enter each
process symbol
• At least one data flow must leave each
process symbol
• Often more than one
DFD Data Store Symbol
• The purpose is to depict a data repository
• The plural name consists of adjectives and a
noun
• Place the data store name between the lines
STUDENTS
PURCHASE ORDERS
DFD Data Store Symbol
• Data store is connected to a data flow with a
proceses at the other end of the data flow
• Detailed contents not shown in the DFD
(find this information in the data dictionary)
DFD External Entity Symbol
• The purpose is to depict the terminators or
boundaries
• A person, department, outside organization, or
other information system that provides data
(orgin) to the system or recieves data (sink) or
information from the system
• Entity is always connected by a data flow to a
process
DFD External Entity Symbol
• The entity name is in the singular form of
the name of the department, outside
organization, other information system or
person
CUSTOMER
PAYROLL SYSTEM
STUDENT
Context Diagrams
Context Diagrams
•
•
•
•
•
Top-level view of information system (IS)
First DFD is general overview of the IS
Shows the boundaries of the IS
One process only (it represents the entire IS)
Add all external entities and connect to process
ORDER PROCESSING (process)
CUSTOMER (entity)
WAREHOUSE (entity)
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Context Diagrams
• The requirements gathering of the systems
analysis phase will define all the external entities
• No data stores at this level of the DFD
• Context diagram must fit on one page
• Process name of the context diagram is the name
of the IS
• Avoid crossing data flow symbols
Diagram 0
Diagram 0 for the context diagram DFD for a grading system.
Diagram 0
• First detailed DFD
• The purpose is depict the major processes,
data flows, and data stores for an IS
• Repeat the external entities and data flows
from the context diagram
• Add major processes and data stores
Lower Level Diagrams
• Expand all processes into functional
primitives
• Functional primitives are processes that
consists of a single function ( can not
expand further)
Data Dictionary
• The purpose is a central storehouse of data about
an IS’s data and the data’s transformations
• Dictionary is used to document the detailed facts
about an IS
Contents of data flows
Contents of data stores
External entities details
Data Dictionary
• Also defines and describes all data elements
and meaningful combinations of data
elements
• A data element is the smallest piece of data
that has meaning within an IS
Salary
student name
Social security number
birth date
Data Elements
• DFD data flow
• DFD data store (data elements logically
combined)
• DFD process (functional primitive)
• External entities (recommended)