Use Case Modeling and Sequence diagrams

Hello all.

I’m trying to write use-cases, with associated system sequence diagrams; I’m able to create use cases and fill the flow-of-events, and then generate the associated sequence diagram.

However, as far as I can see, the interactions in the sequence diagram which can be generated are only actor->system and system->actor; I’d like to add, if possible, system->system steps, in order to explicitly introduce verify steps. Something like:

  1. actor asks the system for a a service, providing some info;
  2. system verifies the info are correct;
  3. system provides the service

Now, the step 2, which is a system-to-system interaction, can’t be directly generated; any suggestion?

Using Visual Paradigm Professional Edition.