UML was missing data flow diagrams for decades (which was - in my eyes - probably the biggest single mistake the UML designers ever made). Data flow diagrams are essential for modeling any kind of system which contains data processing components, with some input data, some processing and some output data. They scale well to several layers of abstraction, and they can be even used for model driven approaches and code generation.
Fortunately, several UML tool vendors provide DFD as an extension to the standard UML diagrams, it seems they understood the need for such diagrams way better than the UML inventors.
Today, the best existing substitution in UML is the Information flow diagram, which was introduced in some time ago in UML 2.x. It seems this type of diagram would be sufficient for your example.