1 / 8

Physical Data Flow Diagrams

Physical Data Flow Diagrams. Process Rules.

benjamincruz
Télécharger la présentation

Physical Data Flow Diagrams

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. PhysicalData Flow Diagrams

  2. Process Rules • Process1. No process can have only outputs. It is making data from nothing. An external entity can have only outputs (a source).2. No process can have only inputs (a black hole). An external entity can have only inputs (a sink).3. A process has a name which implies an action.

  3. Data Store Rules • Data Store 4. Data cannot move directly from one data store to another data store. Data must be moved by a process. 5. Data cannot move directly from an external entity to a data store. It must be retrieved from the external entity by a process and placed in the store. 6. Data cannot move directly from a data store to an external entity. It must be moved by a process. 7. A data store has a name which describes its content.

  4. External Entity Rules • External Entity 8. Data cannot move directly from one external entity to another. A process moves data. Otherwise do not show the movement. 9. An external entity has a name which describes its role (noun). Not an action(verb).

  5. Data Flow Rules • Data Flow 10. A data flow has only one direction. If data flows in both directions between a process and a store then it should be shown with two separate arrows. 11. A fork in a data flow means that exactly the same data flows to two or more separate places. 12. A join in a data flow shows that exactly the same data can come from two or more places

  6. Data Flow Rules • Data Flow13. A data flow cannot go back directly to the same process that it leaves. There must be a least one other process which handles the data flow, produces some other data, and returns the original data flow to the beginning process. 14. A data flow to a data store means update (delete or change). 15. A data flow from a data store means retrieve or use. 16. A data flow has a name which describes its content.

  7. Physical DFD • Shows actual implementation • Usually of current system • Showing tasks and how they are performed and by whom • Can include names of • people, departments, documents, files, devices.

  8. Context Level The Context Level – just one process – flows are compatible with flows in/out of Level 1 processes – shows the external entities – may draw an external entity box more than once, indicate this by line across corner

More Related