Modeling Data Exchange

Dear all,
I am struggeling with a certain question for days and can find now answer. I wan’t to model a software in the manner a class diagram. In particular, the diagramm should depict functional bulding blocks, data sources and what data is exchanged between these components. Is a class diagram the right model for that? And if so, how do I model the data exchange?

I am confident that I can model data sources and functional bulding blocks as classes. I can also model which classes exchange data by using relations. But how do I denote what information is exchanged?

It would be really really great if somebody could help my.

Thanks alot,