Process Modeling: Context Diagrams and Data Flow Diagrams

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MIS 374 Rev 02

Process Modeling: Context Diagrams and Data Flow Diagrams (DFDs) Introduction
Figuring out the business processes for complex systems can be complicated. For example, if the goal is to streamline an existing supply chain process, your investigation will cross multiple business units, perhaps starting with an on-line order, a retail store pick-up, or a telephone order. How does the current process work to replace items in inventory storage and on retail shelves? Computer systems make these processes faster, but often increase complexity. As a business analyst, programmer analyst, or IT auditor you are likely to need a graphical technique to help investigate and document current processes and work with a team to determine where problems occur and what the best solution is. Graphical process models are a common part of Root Cause analysis to determine exactly where problems occur. Graphics help teams communicate what software needs to be created or fixed based on a view of what data must be processed to meet and fulfill system requirements.

A data flow diagram (DFD) is a drawing that shows how a system's environmental entities, processes, and data are interconnected. Using four simple symbols users can show developers their current system processes and what they would like to change. The only four symbols are shown in Table 1 below.

Table 1. Data Flow Diagram Symbols

A square is an Environmental Entity (EE)—a source of, or destination for, data outside the system. An arrow is a data flow. Each data flow must have a unique identifier.

A process bubble is a process that changes data. Process bubbles should be numbered at the top. The Process Label should be in a verb – object format. The bottom section identifies an actor or system component.

An open rectangle is a data store. unnumbered process bubble in the shape of a circle to represent the entire system. Figure 1 shows the context diagram for the initial investigation of the existing Latinitas ―system‖ with a single process bubble in the middle. Its five environmental entities are represented by squares surrounding the single system process bubble. The system is connected to its environmental entities by arrows that represent data flows. Notice how many data flows

The Context Diagram
DFDs exist in a hierarchy, beginning with the simplest, highest, system level and ending with the lower level diagrams with detailed processes. The DFD at the system level illustrates the context, that is, the circumstances of its environment and is called the context diagram. This diagram contains only a single,

©Eleanor Jordan 2011. All rights reserved.

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Process Modeling

Process Modeling
surfaced in the team’s discussions with Angie about her work with Latinitas donors, volunteers, and interns. When Angie posted her request for an MIS 374 ―Volunteer Database‖ she had not

MIS 374 Rev 02
thought through her real needs. White-boarding with her MIS 374 development team was a learning experience for Angie as well as the team.

Figure 1. Latinitas Current System - Context Diagram

The Figure 0 Diagram
A DFD diagram on a lower level ―explodes‖ a process on the level immediately above, providing more detail. The DFD on the second level from the top in the hierarchy is the Figure 0 diagram. Each process of the Figure 0 diagram is numbered from left to right and then down. In order to prevent a DFD from becoming cluttered, the general rule is to keep the number

of processes to seven or less. This rule applies not only to the Figure 0 diagram but to DFDs on the lower levels as well. Figure 2 shows the Figure 0 diagram of the Latinitas system. The system contains four main processes: Manage Interns, Manage Volunteers, Organize Fund Raising Events, and Determine Needs for Funds.

©Eleanor Jordan 2011. All rights reserved.

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