My client has a simple business requirement but I got confused on how to achieve it by SharePoint. They want to build several forms which allow users to manually input data and save them to separated SQL Server. Some workflows (OODB Workflow or Nintex) will be created for notification and automatic processes on the forms.
Initially, the client just thinks about On-Premises deployment but O365 should be considered when designing the solution.
At first, I plan to create forms by Application Pages which allow me to interact with SQL Server freely. But don't know how to implement workflow as data is not kept in SharePoint lists. Also, with this approach, I will get stuck with the application pages if client request to move to O365.