A flowchart is a common type of diagram, that represents an algorithm or process, showing the steps as boxes of various kinds, and their order by connecting these with arrows. This diagrammatic representation can give a step-by-step solution to a given problem. Data is represented in these boxes, and arrows connecting them represent flow / direction of flow of data. Flowcharts are used in analyzing, designing, documenting or managing a process or program in various fields.
Symbols
A typical flowchart from older computer science textbooks may have the following kinds of symbols:
- Start and end symbols
- Represented as circles, ovals or rounded rectangles, usually containing the word "Start" or "End", or another phrase signaling the start or end of a process, such as "submit enquiry" or "receive product".
- Arrows
- Showing what's called "flow of control" in computer science. An arrow coming from one symbol and ending at another symbol represents that control passes to the symbol the arrow points to.
- Processing steps
- Represented as rectangles (or oblongs). Examples: "Add 1 to X"; "replace identified part"; "save changes" or similar.
- Input/Output
- Represented as a parallelogram. Examples: Get X from the user; display X.
- Conditional or decision
- Represented as a diamond (rhombus). These typically contain a Yes/No question or True/False test. This symbol is unique in that it has two arrows coming out of it, usually from the bottom point and right point, one corresponding to Yes or True, and one corresponding to No or False. The arrows should always be labeled.A decision is necessary in a flowchart. More than two arrows can be used, but this is normally a clear indicator that a complex decision is being taken, in which case it may need to be broken-down further, or replaced with the "pre-defined process" symbol.
A number of other symbols that have less universal currency, such as:
- A Document represented as a rectangle with a wavy base;
- A Manual input represented by parallelogram, with the top irregularly sloping up from left to right. An example would be to signify data-entry from a form;
- A Manual operation represented by a trapezoid with the longest parallel side at the top, to represent an operation or adjustment to process that can only be made manually.
- A Data File represented by a cylinder.
Flowcharts may contain other symbols, such as connectors, usually represented as circles, to represent converging paths in the flowchart. Circles will have more than one arrow coming into them but only one going out. Some flowcharts may just have an arrow point to another arrow instead. These are useful to represent an iterative process (what in Computer Science is called a loop). A loop may, for example, consist of a connector where control first enters, processing steps, a conditional with one arrow exiting the loop, and one going back to the connector. Off-page connectors are often used to signify a connection to a (part of another) process held on another sheet or screen. It is important to remember to keep these connections logical in order. All processes should flow from top to bottom and left to right.
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