Data flows: Note on Data-Driven Process Modeling

A Focus on Data
Data flow diagrams (DFDs)
Common DFD mistakes
Summary/next steps

Data Flow Diagramming

In this course we will use data flow analysis to understand patterns of data movement within processes. DFDs provide one technique for isolating the data stores used by a process and the major data entities that those stores contain.

Data flow diagrams (DFDs) offer a graphical technique for summarizing the movement of data between the processing steps that occur within a business process. They isolate the collections of data, or data stores, which accumulate during a process, and identify the sources of data that arise outside process boundaries. Some key characteristics of data flow diagrams are:

Symbols used in DFDs

Table 1 summarizes the graphical symbols used in data flow diagrams. The vocabulary used by DFDs is very simple, comprising only four symbols: data flows, processing steps, sources/sinks, and data stores.

see also [2]

An example can probably provide the best way to understand how a data flow diagram can summarize knowledge about a process. The diagram on the next page illustrates how a systems analyst might use a DFD to describe data flows, processing steps, sources, sinks, and data stores used to describe an individual's relationship with his or bank. The DFD describes the processing transactions that take place as the individual and the bank jointly manage a set of customer accounts. The process(es) described include most operational aspects of handling the customer's money, including making deposits, funding withdrawals, paying bills (perhaps a service provided by electronic banking), and reconciling account balances. Some of the data stores can be translated almost directly into database specifications (e.g., "Account transactions"). Others show how the notion of data stores can apply equally well to data that are captured in paper form (e.g., "Monthly account statements"). Throughout, the data flow arrows identify data items and groups of data items that move between sources, data stores, and processing steps. Note that processing steps represent those points at which data from sources and data from data stores come together, resulting to some change in specific data items maintained by the bank.

Source: Adapted from Figure 9.3, p. 351 in Whitten, J. L.; Bentley, L. D.; Barlow, V. M. (1994). Systems Analysis and Design Methods (Third Edition). Burr Ridge, IL: Irwin.

What are some of the advantages of using DFD analysis? Here are several:

Next: Common DFD mistakes

@ 1999 Charles Osborn