System diagram conventions

A system diagram is a form of notation that represents the parts, processes and connections in a system. It has no fixed list of components: what appears depends entirely on the system you are describing.

No fixed parts

One diagram might need only a few devices, such as two classroom tablets, a teacher's laptop and a printer. Another might need a booking webpage, a card payment service, a calendar database, a caretaker and the people hiring a village hall. Neither list is more correct than the other. The diagram is built around the system in front of you, so diagrams of different systems can look very different. Two people may even represent the same system in different ways.

No set method

Unlike a flowchart, which uses set shapes and arrows to show the order of steps, or a data flow diagram, which has rules for its symbols and connections, a system diagram has no prescribed construction method. You arrange the parts in a way that makes sense for the system and the audience. That makes system diagrams flexible, but it also means a reader cannot decode one from symbols alone.

Labels and descriptions

Because there are no compulsory symbols, labels and short descriptions are sometimes added. A label might name a part, such as calendar database, or explain a process, such as checks whether a hall is free. A description beside a line might say booking details to explain the connection. These labels and descriptions help the reader understand the diagram, but they are not a required set of symbols. The reader must use the labels and their own knowledge of the system to work out what it shows.