Preparing a Context Data Flow Diagram
WHY:
This activity is designed to give you practice using System Architect to design and draw Context Data Flow Diagrams. You will use DFDs to model the activities in the current system pertaining to your project. Data Flow Diagrams have many uses in Systems Analysis, Planning, and Design, because of their versatility in modeling different levels of detail.

LEARNING OBJECTIVES:
Understand how to prepare a Context DFD.
Discover how to use System Architect to develop process models.
Discover how to control the placement of symbols in a System Architect diagram.
PERFORMANCE CRITERIA:
Quality of the answers to the Critical Thinking Questions.
Completeness
Clarity
Depth
Quality of the Context DFD.
INFORMATION:
Process
A process is work or actions performed on incoming data flows to produce outgoing data flows. Processes focus on what work or action is being performed, not on who or what is doing the work. A process is represented by a rounded rectangle.


Data Flow
A data flow represents a highway over which data travels as input to some processes and output from others. A primitive data flow is one whose attributes always travel together as a single packet. A composite data flow is one that consists of multiple primitive data flows. A data flow is represented by a connector.


External Agent
An External Agent is usually a source of inputs to the system or a receiver of outputs from the system and is represented by a square.


Data Store
A data store is an inventory of data. It represents all the occurrences of a data entity. A data store is represented by an open-ended rectangle.
RESOURCES:
System Architect Help System and Manuals;
Class Activity 8;
Chapter 6, Systems Analysis and Design Methods
40 minutes
PLAN:
Choose roles if you have not already done so.


Review the model in activity 8 and answer the Critical Thinking Questions from that activity.


Using the system description below, develop a context data flow diagram using System Architect's Data Flow Diagram facility.


The purpose of the CAMPAIGN PLEDGE SYSTEM is to collect pledges from DONORs during a capital campaign and ensure that these pledges are honored with donations. The BOARD OF TRUSTEES sets up a capital campaign, determines the campaign categories for which pledges may be sought, and sets a goal for these categories. The college uses a list of prospective donors prepared by the development office to solicit donors to make pledges and/or donations toward one or more of these pledge categories. The solicitation includes a pledge form which the donor completes giving her information and the pledge amount. Once a DONOR has pledged to contribute, the development office sends pledge reminders at the appropriate times, and the DONOR sends back her pledge payment with a copy of the reminder invoice. The payments and invoices are sent to the BUSINESS OFFICE which records and deposits them. The development office keeps track of the total donated by each donor to each campaign category. The system produces a campaign progress report which is sent to the BOARD OF TRUSTEES and a campaign summary report which is sent to the College PRESIDENT. A detailed donor profile report and pledge status report are also prepared for the BUSINESS OFFICE auditors. Exception reports include an inactive donor list and an unfulfilled pledge report. These are sent to the PRESIDENT for information when he contacts donors.

Suggestions for using Systems Architect
Remember to map the Z: drive to \\DIAMOND\CPSC before launching Systems Architect (SA)


When you first enter SA, set the Preferences under the Tools menu so that everything is checked except Edit Attribute in the first column and Verify Dialog and Simultaneous Select/Draw in the second column. Click Save to save this configuration on the desktop for the next time you run SA on that computer.


If you would like more control over how the data flows and other connectors bend, go to Format; Symbol Style; Line and select Straight Orthogonal. Click Save to extend this selection to other diagrams you may draw while working on the current computer. You can then click on parts of the diagram where you want the bends in the lines to go.


If you want to make the area of the diagram that shows on the screen larger, thus making the diagram smaller, choose the Reduced 75% option under the View menu. Be careful when using this option that you do not extend your diagram outside the printed page boundaries.


If you do not like where SA chooses to position your symbols, you should know that the program is using an invisible grid. To reduce the size of the grid lines go to Format and choose Diagram style.


If the diagram symbols keep resizing when you move them or print the diagram, right click on any one of them and open the display mode and click off anythin that has to do with automatic resizing.
CRITICAL THINKING QUESTIONS:
Could the list of prospective donors in the CAMPAIGN PLEDGE SYSTEM be considered an external data store and appear on the context diagram?


Why is it reasonable to divide the CAMPAIGN PLEDGE SYSTEM into the subsystems PLEDGE, DONATION, and CAMPAIGN?

Context Diagram




The Feature-Oriented Domain Analysis (FODA) Context Diagram is a data flow diagram showing data flows between a generalized application within the domain and the other entities and abstractions with which it communicates. One thing that differentiates the use of data flow diagrams in domain analysis from other typical uses is that the variability of the data flows across the domain boundary must be accounted for with either a set of diagrams or text describing the differences.

The following is an example of a context diagram for the Army Movement Control Domain [CMU/SEI-91-SR-3][CMU/SEI-91-TR-28].



In this context diagram, the information provided to and received from the movement control domain is identified. The arrows represent the information received or generated by the movement control domain. The closed boxes represent the set of sources and sinks of information. The open ended boxes represent the databases that the movement control domain must interact with.

In the movement control domain, most of the data is produced or maintained by operations outside the scope of the domain. For example, all data about weather, terrain, and the disposition of friendly and enemy forces is obtained directly from outside the domain, as shown on the context diagram.

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