Should I prepare a research statement or cover letter for postdoc ads. with general descriptions? I noticed 1-2 advertisements for postdoc positions in which they provided the general description of what they want as publishing and improving the state-of-the-art in a more or less big subfield of Y. The ads. were generally asking for sending the documents without specifying what exact documents they want to receive. One of them contained something similar to 


  The exact subject of research depends on your personal preferences, as long as it fits this area.


So, besides sending a CV and academic transcripts, I was thinking about preparing a cover letter or a research statement (or both). The problem is that they did not specify what sort of skills they need or what specific research objectives they are interested in, so I'm afraid how to tailor my cover letter or research statement.

In fact, as the research area is of interest to me I have ideas of what sub-problems are important there and how to approach them generally. However, I do not know if they fit the group's research goals.

Also, when they did not specify, do I have to prepare both the cover letter and research statement?

BTW, I apply in Computer Science in Germany!
Nobody here can know about the documents that are required, but typically a job announcement has a contact person. Ask them about such details.

The position sounds similar to many postdoc positions in mathematics - they want someone who can do research, be useful to the university, and co-operate with locals. I would suggest taking a look at what the faculty and PhD students are doing at the moment and trying to find shared interests there. Check out the faculty website, personal webpages and Google scholar profiles - wherever you can find list of publications.

You do not need to be doing precisely the same thing as they do, as long as you can make a case that there might be cross-pollination and that you will be doing good work.

If there is a current line of research they are pursuing, mention that. If you could help them move or expand their research, also mention that. You are not setting anything in stone, but rather trying to figure out possible shared interests with the locals. The details of what you actually do will get decided once you are there, most likely.