Context Level DFD’s & Level 1 DFD’s

5 Mar

In our course, we need to understand and be able to draw 2 types of Data Flow Diagrams, they are Context Level DFD’s and Level 1 DFD’s. In this blog, I will hopefully make it easier to understand the differences between the two types of DFD’s and help understand how to draw a DFD for the exam. Firstly I will look at Context level DFD’s and give an example. Then I will look at Level 1 DFD’s and give an example.

Context Level DFD’s

A context level DFD is the most basic form of DFD. It aims to show how the entire system works at a glance. There is only one process in the system and all the data flows either into or out of this process. Context level DFD’s demonstrates the interactions between the process and external entities. They do not contain Data Stores.

When drawing Context Level DFD’s, we must first identify the process, all the external entities and all the data flows. We must also state any assumptions we make about the system. It is advised that we draw the process in the middle of the page. We then draw our external entities in the corners and finally connect our entities to our process with the data flows.

Below is an example of a Context Level DFD.

context

Level 1 DFD’s

Level 1 DFD’s aim to give an overview of the full system. They look at the sytem in more detail. Major processes are broken down into sub-processes. Level 1 DFD’s also indentifies data stores that are used by the major processes.

When constructing a Level 1 DFD, we must start by examining the Context Level DFD. We must break up the single process into its sub-processes. We must then pick out the data stores from the text we are given and include them in our DFD. Like the Context Level DFD’s, all entities, data stores and processes must be labelled. We must also state any assumptions made from the text.

Below is an example of a Level 1 DFD.

Level 1

Hopefully this blog has helped to understand the difference between Context Level and Level 1 DFD’s and made it easier to draw them. Please leave any questions or comments below.

Source:

Cathal Doyle Lecture 18.

9 Responses to “Context Level DFD’s & Level 1 DFD’s”

  1. sad111353781 March 5, 2013 at 3:42 pm #

    Very helpful for exam! great blog🙂

  2. sad111419882 March 5, 2013 at 8:35 pm #

    great blog! did an example of one today in a tutorial but I was confused about this topic! this has helped me understand them more🙂

  3. sad111310996 March 6, 2013 at 7:21 pm #

    alot of effort went into it

  4. sad111511053 March 7, 2013 at 9:43 am #

    Excellent blog ! A lot of information in it that im sure will be useful come exam time !

  5. sad109417338 March 10, 2013 at 12:41 pm #

    Thanks for the nice comments!

  6. aryasulistyo! January 5, 2014 at 11:05 am #

    thank you! but may I copy the level 1 diagram?

    I need to do some school’s assignment to “analyze” an example of level 1 diagram. Hope I can use it, with your permission of course.

    p.s: don’t worry I’ll put the site’s name as a source :p

  7. edayal March 6, 2014 at 9:54 pm #

    Here is a template for a Context Level DFD: http://www.hitdocs.com/context-level-dfd-with-groupings-vsd/

  8. SahibJot Singh April 9, 2014 at 3:54 pm #

    where can i find Level 2 DFD’s definition and example?

  9. Prosper Mugova May 19, 2015 at 10:20 am #

    Thanx a lot

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