Lesson 2

In this lesson, you will learn to create a data flow diagram using the Dataflow Diagrammer. Specifically, this will involve the creation of :

• Frame Functions, Local Functions and Global Functions
• Data Flows
• Datastores
• Externals

What is a Data Flow Diagram?A Data Flow Diagram (DFD) is a process-oriented graphical representation of an application system. In the words of Hoffer, George and Valacich (1999), a DFD "is a picture of the movement of data between external entities and the processes and data stores within a system."

Some terms used when working with the Dataflow Diagrammer

A function, in the context of Designer Dataflow Diagrammer, is similar to what is referred to as "process" in the discussion on DFD in your text-book. A "process" is defined as: "The work or actions performed on data so that they are transformed, stored or distributed" (Hoffer, et. al., 1998). Presented below are some types of functions that we will use in our dataflow diagram.

Frame Function is the main function that will contain all the child functions under it.

Local Function is a function within the Frame Function while the Global Function is one that is outside.

A Datastore is a coherent collection of data. In other words, it represents data that is physically stored in locations like folders, notebook, a computer file or a database.

Dataflows represents the flow of data from a store to a function or vice versa

Externals like in the Process Model are organizational units or entities from other applications that can be used in the current application. External entities (externals) may be sources (from which data flows originate) or sinks (in which data flows terminate).

A Brief Narrative for the Dataflow Diagram

In this lesson, we will attempt to represent the processes that are embedded within the Student Registration System using the DFD technique. Let us assume that we have identified four main processes: maintain student records, maintain course information, maintain course enrollment, and list schedule. The process "maintain student records" accepts student information from students (say, during admission) and inserts the student information in the STUD datastore. In addition, this process also handles changes in student information (including changes in address, majors, etc.). The process "maintain course information" is responsible for receiving information about courses to be offered by the university from respective departments, validate the proposed courses, and insert/update CRSE datastore accordingly. If a proposed course is found to be invalid, a notification is sent to the concerned department. The "maintain course enrollment" process handles student requests for enrollment in a particular course. The process, first, checks the student status (e.g., whether full-time or part-time) from the 'STUD' datastore. Next, the validity of the course (e.g., whether the course is being offered) is checked from the 'CRSE' database and the enrollment status (e.g., whether the course is full) is checked from the 'ENROL' database. Once all these have been verified, the student is enrolled by recording this information in the ENROL datastore. If a student is not accepted into the requested course (due to whatever reason), a notification is sent to the concerned student. Finally, the "list schedule" process draws on information stored in STUD, CRSE and ENROL to generate the schedule that is sent to students. See Figure 2.1 for a graphical representation of the DFD that we will generate in the course of this lesson.

Figure 2.1: Graphical Representation of a Dataflow Diagram

To create a Dataflow Diagram:

1. From Repository Object Navigator select Tools Dataflow Diagrammer (See Figure 2.2a) or go to the Designer launch pad and select Dataflow (See Figure 2.2b).

   
   
   Figure 2.2a: Selecting the Dataflow Diagrammer from the Repository Object Navigator

   
   
   Figure 2.2b: The Designer/2000 Launch Pad

2. You will immediately come to the Dataflow Diagrammer Window.
3. Open File -> New. You will then be prompted to Choose Container. Click on the icon that looks like a notepad, and choose the Application System (called STUDENT) that you created in Lesson 1 (see Figure 2.2c). Hit OK to get back to the Choose Container window. Hit OK again.

Figure 2.2c: Choosing Container

4. A window for New Diagram will appear . (See Figure 2.3).
   
   
   Figure 2.3: The New Diagram Window

5. The new Diagram window will not contain any list of functions on which you can base your diagram since you have not created any. You will hence have to create a new function.

6. Select the Create Function Button. Immediately, the Create Function Window will appear. Type in the label and the short definition as in Figure 2.4 and click OK.
   
   
   Figure 2.4: The Create Function Window

7. The DF Diagrammer will create a Frame Function based on the Function that you have created. (See Figure 2.5).
   
   
   Figure 2.5: The Dataflow Diagram with the Frame Function

8. To create the local or child functions, click on the following icon from the toolbar drop it inside the Frame Function.
   

9. Immediately you will see the Create Function window.

10. Type in the label and a short description of the function and click OK. (See Figure 2.6). (Notice that since this is the first Child function we give it a label of SRS1).
    
    
    Figure 2.6: The Create Function Window for creating the Child Function

11. Repeat steps 6,7 & 8 to create three more functions: One named Maintain Course Information with label SRS2, one named Maintain Course Enrollment with label SRS3 and one named List Schedule with label SRS4. Your diagram should now look like the one in Figure 2.7.
    
    
    Figure 2.7: The Dataflow Diagram with the Four Child Functions

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