UML Sequence diagrams

Hi!

I want to describe the process where a system module imports a file either manually or by the autoImport class. And a friend thought I should describe it as a sequence diagram. This chain of events has a few loops in it too. And I ahve never used sequence diagrams to show how a system flow is working. Usually I use to show the "call stack" between a few components, which systems calls that are made and their responses. I never used it to show the flow of a "file import". From txt file to database store.... and in between are a number of modules that do some work ,and in these modules are lots of loops.

Which diagram do you think I should use? Like a simple flow diagram? Im having problems finding an UML diagram that does the trick.. perhaps the use case diagrams...

your thoughts?
Henrik