Data Flow Diagram TutorialObjectivesAfter completion of study of this unit you should be able to:Describe the use of data flow diagramsProduce a data flow diagram from a given case study including different levelsDistinguish between the different categories of data flow diagrams1. Introduction1.1 CASE tools1.2 Development and purpose of Data Flow Diagrams2. Components of Data Flow Diagrams2.1 Components2.2 Hints on drawing2.3 Data flows3. Developing Data Flow Diagrams3.1 Introduction3.2 Context diagram3.3 Level 1 Data Flow Diagram3.4 Lower levels of Data Flow Diagrams3.5 Check list4. Categories of Data Flow Diagrams4.1 Physical4.2 Logical4.3 The relationship between logical and physical Data Flow Diagrams5. An example of the development of a Data Flow Diagram6. Process models7. Summary8. Activities9. Bibliography10. Commentary on activities1. Introduction1.1 CASE tools1.2 Development and purpose of DFDs2. Components of Data Flow Diagrams2.1 Components2.2 Hints on drawing3. Developing Data Flow Diagrams3.1 Context diagram3.2 Level 1 Data Flow Diagram3.3 Lower levels of Data Flow Diagrams3.4 Check list4. Categories of Data Flow DiagramsFigure 13 The progression of DFDs5. An example of the development of a Data Flow Diagram6. Process models7. Summary8. Activities9. BibliographyData Flow Diagram TutorialObjectivesAfter completion of study of this unit you should be able to:- Describe the use of data flow diagrams- Produce a data flow diagram from a given case study including different levels- Distinguish between the different categories of data flow diagrams11. Introduction1.1 CASE tools1.2 Development and purpose of Data Flow Diagrams2. Components of Data Flow Diagrams2.1 Components2.2 Hints on drawing2.3 Data flows3. Developing Data Flow Diagrams3.1 Introduction3.2 Context diagram3.3 Level 1 Data Flow Diagram3.4 Lower levels of Data Flow Diagrams3.5 Check list4. Categories of Data Flow Diagrams4.1 Physical4.2 Logical4.3 The relationship between logical and physical Data Flow Diagrams5. An example of the development of a Data Flow Diagram6. Process models7. Summary8. Activities9. Bibliography10. Commentary on activities21. IntroductionThis unit deals with one of the major techniques for recording the requirements of a user for a new computer application. An initial diagram is constructed to show the processes which are being implemented in an existing system. The diagram helps to show how information is used to produce the functions that are required by the current system. It also shows what information is provided to the systemand what information is provided form the system. Other benefits include the documentation of who is using the system and what data will be stored. By careful construction of the DFDs (data flow diagrams) the boundaries of the system to be built may be clearly identified. This helps to clarify what will and whatwill not be constructed. It will also show the interaction that may be required with other systems.The data flow diagrams should also have some associated documentation. This is necessary as the diagrams are meant as a visual representation of the way in which information is processed. There is limited space on the diagrams so that documentation to explain, refine and describe further details of whatis shown need to be kept somewhere in the proposed system documentation. The data flow diagrams and the associated documentation together combine to form a data flow model. This is also commonly called a process model.The user requirements when complete are used as a basis for the development of the system. Later when the system has been developed it can be tested against the initial requirements to see whether the user’s needs have been met.1.1 CASE toolsFor many ways of developing and implementing new systems, software is available to help the systems analyst produce what is required. This software is called a CASE tool. CASE stands for Computer Aided Software Engineering. Data Flow Diagrams are usually produced using a CASE tool although they can beproduced simply with a pencil and paper. The diagrams shown in this unit were developed using SELECTSSADM Professional version 4.1.1.Using a CASE tool for construction of the DFDs has many advantages. It is not just a drawing tool. Firstly the CASE tool will not allow a non-standard use of notation for all the items in the diagrams. Secondly it applies some rules so that designing the diagrams prevents the users from making connectionsbetween the different items that should not be allowed. There is also some checking that may be invoked to alert the designer to some potential errors. As we will see the CASE tool helps to check that the DFDs are consistent with other views of the system which require diagrams that may also be drawn with the CASE tool.You would find it helpful to become familiar with a CASE tool to practice some of the example activities in this unit.31.2 Development and purpose of DFDsBefore attempting to construct an initial DFD it is necessary to gather and digest information that helps usto understand how data is processed in the current system. Fact-finding techniques are used for this purpose and are discussed in another Unit. As the DFD is constructed a systems analyst will often come across areas of doubt where the precise way to model the system is unclear. This is a natural part of the development and should not be regarded with alarm. In fact, it is expected and it is a consequence of attempting to model the current situation that questions will be asked to clarify the exact processes which are taking place. Sometimes the analyst will make an assumption and then check this with the user at a subsequent meeting.Results of interviews, documents, reports, questionnaires etc. will all play a part in helping the analyst to gain an insight into the current processes. Where a system is being developed form scratch the analyst will work with the user to develop the proposed DFDs.When all the information about the current system is gather it should be possible to construct the DFDs toshow:- the information that enters and leaves the system- the people/roles/other systems who generate and/or receive that information- the processes that occur in the system to manipulate the information- the information that is stored in the system- the boundary of the system indicating what is (and what is not) includedAs a staring point, it is sometimes useful to construct a document flow diagram. This