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Conditional expression in data flow diagram?

Is it allowed to create a conditional statement in DFD? Do I need to show confirmations and conditional statements when creating a DFD or just its data stream?

For example, when creating a DFD for the login page in a web application, I am going to show whether the user is valid or not?

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In general, DFDs do not show the conventions as such, nor do they show the location where the process is running, or the sequence of operations. You need to see DFDs as functions that return something based on their input parameters.

The login screen is likely to be a process that reads the user credentials and returns the user ID or nothing if the user is invalid. You can see two outgoing streams in cases when you want to do something special if the user is invalid. Or it may return the reason the user is invalid (unknown user, incorrect password, account has expired). Clarifying these goals is the goal of DFD modeling, so the answers depend on your project.

In general, one must resist the temptation to add too much detail to the DFD.

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I think what you ask is called Transaction Flow. Basically, you are using a transaction that starts a data stream along the way. Roger. S. Pressman defines it with an example.

Software Development: The 6th Edition Practitioner's Approach. Chapter 10.6.2.

https://books.google.es/books?id=bL7QZHtWvaUC&lpg=PR13&ots=O6v89MxK8l&dq=pressman%2010.6.2&hl=es&pg=PA276#v=onepage&q=pressman%2010.6.2&f=false

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Source: https://habr.com/ru/post/1397394/

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