23-07-2012, 12:46 PM
Data Flow Diagrams (DFD) and Context diagrams
SD-Design-Tools-DFD.ppt (Size: 606.5 KB / Downloads: 32)
Context Diagram
A high-level Data Flow Diagram (DFD).
Shows a system in relation to other external systems
Does not show details within the system
The simplest form of a DFD.
DFD/Context diagram shapes
External Entity: sources or destinations of data
Data Flow: movement of data.
Data Store: where data is stored (e.g. database)
External Entities:
Can be duplicated on the diagram one or more times, to avoid line crossing.
Are not part of the system being studied.
May be part of the same organisation, but are beyond the influence of the system being described.
Data Stores:
Where data is stored
They look the same whether stored electronically (e.g. Database) or manually (e.g. paper files)
Must be named
Can be duplicated one or more times to avoid line crossing.
Can be shared by two or more systems.
Contents of datastore are detailed elsewhere in a data dictionary.
Sometimes show as