Data Flow Diagram (DFD) Question about how to link caching system with the main API

Question

I’m trying to build a DFD diagram but I was confused about caching system which is used to make the data run faster.

Is the diagram below in correct order or should I make another link from caching system to the database?

Answer 1

The diagram uses the Yourdon/DeMarco notation. There is only one active process The Core Application API. The Caching System and the MySQL Database are both data stores. According to Yourdon/DeMarco, a data store is:

a repository of data, a time-delayed data flow, a file

All a data store can do, is to store and retrieve data at the request of a process. But it is not itself process data and interact directly with other data stores. So there shall not be a direct link between the cache and the database.

If your Core application API manages the cache, your diagram is fine. I'd nevertheless rename Caching system (which suggest an active process) to Cache (which better reflects a repository).

If not, and if the cache system manages itself in direct interaction with the database, you would need to transform it into a separate process Cache system which you'd insert in the flows between your core application and the database. This new process should then have flows with the database, with the application process and a new Cache data store.

Btw, I'd recommend to remove API from the name of your process: the API is just the interface to the application and not the application itself.