1/13/2015
Systems Analysis
DATA FLOW DIAGRAMS
• Focus is the logical view of the system, not the
physical
• “What” the system is to accomplish, not how
• Tools:
– data flow diagrams
– data dictionary
– process specification
– entity-relationship diagrams
Data Flow Diagram
The purpose of data flow diagrams is to
provide a semantic bridge between users and
system developers.
“DFD is a network representation of a system. The
system may be automated, manual, or mixed. The
DFD portrays the system in terms of its component
pieces, with all interfaces among the components
indicated."
- Tom DeMarco
Hence DFDs:
focus on the movement of data between external
entities and processes, and between processes and
data stores
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1/13/2015
Example Data Flow Diagram
data store
data flow
process
external
entity
Why Conduct Process Modeling?
• Understand components of current logical or
physical system for purpose of rebuilding in
a different physical form/technology,
possibly with some changed functionality
• Find inefficiencies in current system
• Re-engineer current system
Data Flow Diagrams are
• Used to perform structured analysis to
determine logical requirements
• A graphical tool, useful for communicating
with users, managers, and other IS
personnel
• Useful for analyzing existing as well as
proposed systems
• A relatively simple technique to learn and
use
Sources/Sinks (External Entities)
• Any class of people, an
organization, or another
system which exists outside
the system you are studying.
• Form the boundaries of the
system.
• The system and external
entities exchange data in the
form of data flows.
• Must be named, titles
preferred to names of
individuals - use a noun
source/
sink
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Some Rules for External
Entities
• External people, systems and
data stores
• Reside outside the system, but
interact with system
• Either a) receive info from
system,...