The following notes were taken during a lecture in COMP 230 Systems Analysis & Design at Camosun College by Marla Weston.  These notes are here mainly to help me study, but if you can find some guidance through them then all the better!

Data Flow Diagrams (DFD)

• Technology independent
• show data flows, structure, and functional requirements of new system
• Useful for depicting purely logical information flows
• DFDs that detail physical systems differ from system flowcharts which depict details of physical computing equipment

Process: work or actions performed on data (inside the system)
Data store: data at rest (inside the system)
Source/sink: external entitty that is orgingin or destination of dara (ouotside the system)
Data flow: arrow depicting movement of data.
Context Diagram: is an overview of an organizational system that shows:

• the system boundaries
• external entities that interact with the system
• major information flows between the entities

Level-0 Diagram

DFD Rules

There are DFD guidelines that apply:

- the inputs to a process are different form the outputs of that provess
- no process can only have outputs or only inputs. processes must have both inputs and outputs.
- process labels should be verb phrases
- all flows to or from a data store must move through a process
- no data move directly between external entities without going through a process
- bidirectional flwo between process and data store is represented by two separate arrow (no bi-directional arrow)
- forked data flow must refer to exact same data item (not different data items) from a common location
- joined data flow must refer to exact same data item (not different data items) from multiple souces to a common location
- data flow caonn go diretly from a process to itself (no recursive data flows)
- data flow from  a process to a data store means update( insert, delete or change)
Functional decomposition is an iterative process of breaking a system description down into finer and finer detail.

• creates a set of charts in which one process on a given chart is explained in great detail on another chart.
• continues until no sub process can logically be broken down any further

Primitive DFD – the lowest level of a DFD.
level 1 diagram results from decomposition of level 0 diagram
BPR: Business Process Re-engineering