While searching for the answer, I found that in the Gane & Sarson notation, duplicate data stores are indicated by adding an extra line. Another website suggested adding an asterisk next to the data store name. However, I was unable to find any answers specific to the Yourdon DeMarco notation.
Is there a generally accepted way to represent duplicates in the Yourdon DeMarco notation? Or should I adopt one of the methods stated above?
I asked this question in StackExchange and got an answer.
To summarise the answer, the Yourdon Demarco notation avoids duplication where possible because it makes it difficult to visually follow the flow, and this is the practice that should be adopted if possible.
However, in cases where duplication cannot be avoided, there are 2 ways to represent it:
Make no graphical difference between the duplicate stores. This was the approach used in the Yourdon & Demarco book.
Use an asterisk exponent behind the store name, and add a legend for the asterisk. This representation can be used if attention needs to be drawn to the duplication.
(Edit: added more details)