I'm working on a software and hardware system which is completely autonomous in its activities. There is no user involved and one external system which data is sent to. There are a lot of different activities and processes going on inside the system, but they cannot be modelled well with use cases as these are all internal. There is, however, one use case and that is sending the data to the external system, but it is not very representative of the system.
I am developing this project using SCRUM and wanted to have some use cases or user stories to base my sprints on or build part of my backlog with. In our team we have traditionally used these to do this. I was thinking about using something like process models for these activvities but it seems non-standard and slow or hard to explain to my manager and client.
What are alternatives to representing a userless system in such a way that it is clear to business and IT stakeholders and, less importantly, can be used as the basis for agile sprints, much like use cases and user stories?