How do I represent parallel (multiple) inputs in a UML Sequence diagrams?

Question

I am new to UML sequence diagrams. I saw a few YouTube videos and a few tutorials such as this one.

I have a system with multiple inputs, that can interact with the system asynchronously. For example, first the input 4 (out of 5), secondly the input 1 (out of 5), etc. How do I represent them in a UML Sequence diagram?

• user188153: What do you think is an input (/with respect to SDs)?

Answer 1

An UML sequence diagram shows an example sequence of events/calls that happen for an interaction of a single actor with the system.

If you have multiple interactions with the system that can happen in various orders, but they don't directly affect each other (for the processing of input 1 it doesn't matter if input 2 is also being processed at the same time), then you would draw separate sequence diagrams for each interaction.

If the processing does depend on which inputs are active at the same time, then you can

• try to draw the possible combinations in one diagram
• create separate diagrams for each combination, especially if the order of activation is also relevant
• come to the conclusion that sequence diagrams are not the right tool for this case.