Flowcharts

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Introduction

Flowcharts are best suited to showing the flow of control or information, or for illustrating algorithms. They are also good for showing the dependency of operations in a system, such as timing, or critical paths.

Symbols

There are a great many different symbols that can be used in flowcharts, and many industries have their own specialized set of symbols that are commonly-understood within that industry (although sometimes the same symbols are used for different purposes in different industries). When developing flowcharts for a particular industry, you should use the symbol set for that industry. When developing non-industry-specific flowcharts you should adopt a suitable set of symbols, and then use these symbols consistently throughout the documentation. You should also produce a 'glossary', describing the meaning of each of the symbols that you use.

When developing flowcharts for non-technical people, you should be very careful about the choice of symbols. Although different symbols may well exist for different activities or operations, if the users do not understand these different symbols, there is no point in using them. A flowchart that uses a plain rectangle for all activities, actions, and data sources will be more useful than a flowchart that uses different symbols if the user does not understand these symbols.

Commonly-understood symbols

From experience, there are really only three symbols that are commonly understood by most users:

	A rectangle to represent an action or operation. The text within the symbol should clearly summarize the action or operation.
	A diamond to represent a decision. The text within the symbol should be a question. Questions are best worded as yes/no questions, to allow one line into the symbol and two out.
	A rectangle with a wavy bottom edge to represent a paper document or report.

Additional symbols

If you use any symbols other than the coomonly-recognized smbols described above, you should be sure that your readers will understand them. If in doubt, produce a key or glossary and describe them there. The following symbols are often also seen in flowcharts:

	A rectangle with side-bars to represent another process (other than the one that the flowchart is documenting). The text within the symbol should be the exact title of the referenced process.
	A 'drum' (derived from a symbol for a magnetic disk pack) to represent a data source either to which data is written or data is retrieved. Note that data sources are sometimes omitted from business process flowcharts, due to the difficulty in including all data sources for all activities.
	Small circles are often used for off-page connectors (that is, where a single flowchart stretches over more than one page). Each circle should contain an identifier (typically a single letter) that matches up with a connector containing the same identifier on the continuation page. As far as possible, connectors should be aligned across the pages, so if connector 'A' is in the third colum at the bottom of page one, it should also appear in the third column at the top of page two. This makes flipping between the flowcharts easier, and also makes it easier to print out and sellotape the pages together, for workshops and so on.

Lines

Flowchart symbols obviously should be connected via lines, showing the flow (of data or control) from one activity to the next. Generally, lines are shown as follows:

	Lines should always have arrow-heads, to identify the direction of the flow. Lines should also be drawn to flow along a horizontal and vertical grid, rather than diagonally, as shown here.
	Where lines change direction, they should be shown with rounded corners. This makes it easier to identify the directional flow, especially where lines converge, or split in multiple directions.
	Where lines intersect, they should be drawn with 'jumps' (typically on the horizontal line) to make sure that it is clear that the lines do not 'join'.

By convention, lines are shown in a uniform weight, and always solid. However, it is possible to provide an additional level of information by varying the lines according to the type of flow that is taking place. For example, communications (versus lines simply identifying the sequence of activities) could be shown in a different weight or color, or a dotted line could be used to identify a delayed trigger. Note that any such variations would need to be clearly explained by way of a glossary or key.

Variations

The above symbols constitute the absolute basic set of symbols required for a simple flowchart. Although many industries have their own symbol sets, it may be sufficient to develop variations on the basic symbols, to provide additional information. Some possibilities are described below.

	Here, the standard 'Task' symbol has been given a 'drop shadow' to identify tasks that are carried out within a computer system (versus manual tasks, which would be represented by a 'Task' symbol without a drop shadow). A further enhancement could be to vary the color of the shadow to differentiate between multiple systems.
	In this example, the standard 'Task' symbol has been amended to include the transaction (system code) used to execute the task. An alternative would be to provide a reference to the user procedure that explains how to carry out the individual task.
	Another variation on the standard 'Task' symbol, this one is used to identify sub-processes (within the process being documented - compare and contrast with the standard 'Process' symbol, above) for which a separate flowchart exists.

Further information

• BS 4058:1987 Specification for data processing flow chart symbols, rules and conventions
• ISO 5807-1985 Information processing -- Documentation symbols and conventions for data, program and system flowcharts, program network charts and system resources charts