Data Flow Diagrams (DFD)

This example was redesigned from the Wikipedia file: LastResortHotel BookRoom Process.png. [en.wikipedia.org/ wiki/ File:LastResortHotel_ BookRoom_ Process.png]
This file is licensed under the Creative Commons Attribution-ShareAlike 3.0 License. [creativecommons.org/ licenses/ by-sa/ 3.0/ ]
"Event partitioning is an easy-to-apply systems analysis technique that helps the analyst organize requirements for large systems into a collection of smaller, simpler, minimally-connected, easier-to-understand ‘mini systems’ / use cases. ...
Defining requirements.
Single process in a fictitious hotel using data flow diagram notation.
Single use case in a fictitious hotel using use case diagram notation.
This approach helps the analyst to decompose the system into ‘mentally bite-sized’ mini-systems using events that require a planned response. The level of detail of each response is at the level of ‘primary use cases’. Each planned response may be modelled using DFD notation or as a single use case using use case diagram notation.
The basic flow within a process or use case can usually be described in a relatively small number of steps, often fewer than twenty or thirty, possibly using something like ‘structured English’. Ideally, all of the steps would be visible all at once (often a page or less). The intention is to reduce one of the risks associated with short-term memory, namely, forgetting what is not immediately visible (‘out of sight, out of mind’). ...
Single process in a fictitious hotel using data flow diagram notation." [Event partitioning. Wikipedia]
The DFD example "Last resort hotel book room process" was created using the ConceptDraw PRO diagramming and vector drawing software extended with the Data Flow Diagrams solution from the Software Development area of ConceptDraw Solution Park.

"Data flow diagrams are one of the three essential perspectives of the structured-systems analysis and design method SSADM. The sponsor of a project and the end users will need to be briefed and consulted throughout all stages of a system's evolution. With a data flow diagram, users are able to visualize how the system will operate, what the system will accomplish, and how the system will be implemented. The old system's dataflow diagrams can be drawn up and compared with the new system's data flow diagrams to draw comparisons to implement a more efficient system. Data flow diagrams can be used to provide the end user with a physical idea of where the data they input ultimately has an effect upon the structure of the whole system from order to dispatch to report. How any system is developed can be determined through a data flow diagram model.
In the course of developing a set of levelled data flow diagrams the analyst/ designers is forced to address how the system may be decomposed into component sub-systems, and to identify the transaction data in the data model.
Data flow diagrams can be used in both Analysis and Design phase of the SDLC.
There are different notations to draw data flow diagrams (Yourdon & Coad and Gane & Sarson), defining different visual representations for processes, data stores, data flow, and external entities." [Data flow diagram. Wikipedia]
The DFD (Yourdon and Coad notation) example "Process of account receivable" was created using the ConceptDraw PRO diagramming and vector drawing software extended with the Data Flow Diagrams solution from the Software Development area of ConceptDraw Solution Park.